LRT2026 - Low Radioactivity Techniques

21 Sept 2026, 09:00 → 24 Sept 2026, 17:30 Europe/London

The Guildhall (The Guildhall, York)

The LRT2026 workshop will run from Monday 21st to Thursday 24th September (4-days), hosted at the Guildhall in the city of York, United Kingdom. This will be an in-person workshop. There will also be the opportunity for a limited number of attendees to visit the nearby Boulby Underground Laboratory on Sunday 20th September and Friday 25th September 2026.

The Low Radioactivity Techniques (LRT) workshop series examines topics in low-radioactivity materials and techniques that are fundamental for quantum information science and rare-event searches, including dark matter, solar neutrinos, double-beta decay, long half-life phenomena and nuclear astrophysics. The workshop features updates from underground laboratories around the globe. as well as the latest information regarding all aspects of low background detectors, techniques and assay programs in addition to more recent developments.

The workshop features updates from underground laboratories around the globe as well as the latest information regarding all aspects of low background detectors, techniques and assay programs in addition to recent developments in advanced machining and 3D printing using ultra-pure materials.

The goal of this workshop series is to bring together experts in this field for presentations and discussion broadly covering topics related to low radioactivity techniques. The intention is to foster and continue the collaboration and resource sharing required for new generations of detectors to be developed at underground facilities.

The workshop is being hosted by STFC Boulby Underground Laboratory and the University of York, in York, United Kingdom.

Initiated by the Sudbury Neutrino Observatory in 2004, the 2024 meeting is the 9^th international topical workshop in the LRT series:

• LRT2024 hosted by the Jagiellonian University in Kraków, Poland
• LRT2022 co-hosted by South Dakota Mines and the Sanford Underground Research Facility (SURF) in Rapid City, USA
• LRT2019 hosted by the Laboratorio Subterráneo de Canfranc (LSC) in Jaca, Spain
• LRT2017 hosted jointly by the Institute for Basic Science (IBS) Center for Underground Physics (CUP) and Ewha Womans University in Seoul, South Korea
• LRT2015 hosted jointly by PNNL and the University of Washington in Seattle, USA
• LRT2013 hosted by Laboratori Nazionali del Gran Sasso (LNGS) in Assergi, Italy
• LRT2010 hosted by SNOLAB in Sudbury, Canada
• LRT2006 hosted by Laboratoire Souterrain de Modane (LSM) in Aussois, France
• LRT2004 hosted by SNO at Laurentian University in Sudbury, Canada

LRT2026 Call for Abstracts Announcement.pdf

LRT2026 Registration OPEN Announcement.pdf

Monday 21 September

Registration

Registration from 09:00-10:00

Delegates can arrive from 9am for registration, coffee & pastries

Welcome and Introductions

1 Welcome

Speaker: Paul Scovell (STFC)

LRT Intro.pdf

Underground Labs

Convener: Paul Scovell (STFC)

2 Underground Lab Review

Speaker: Sean Paling (STFC)

LRT2026_UGLabs_Paling_Final.pdf

3 Boulby Underground Laboratory Overview

Speaker: Beth Green (Boulby Underground Laboratory)

LRT 2026 Boulby Underground Laboratory [Auto-saved].pdf

4 Introduction of CJPL and its low background facilities

China Jinping Underground Laboratory (CJPL) is one of the deepest (2400 rock overburden) and largest (>300,000 m$^3$) underground laboratory worldwide. This talk will introduce the latest statues of CJPL with focus on the low background facilities: the large liquid nitrogen shielding, large pure water shielding, combined shielding facilities and the ARGUS multi-detector $\gamma$-spectrometers. Also, the latest scientific activities in CJPL, including dark matter searches, neutrinoless double beta decay searches, nuclear astrophysics experiment, super conducting quantum experiment, will be introduced.

Speaker: Wenhan Dai (Tsinghua University)

CJPL-LRT-V2-20260920.pdf

5 1500 Meters Beneath the Alps: Toward a Swiss Low-Background Laboratory in the Bedretto Tunnel

The search for rare physical processes relies on ultra-low-background environments, making deep underground laboratories indispensable. The Bedretto tunnel, situated within the Gotthard massif in Switzerland, is a strong candidate for a future low-background facility, offering an overburden of up to 4000 meters water equivalent. The site is already home to the Bedretto Geology Laboratory run by ETH Zürich. With horizontal access and located within two hours of Zürich and Milan, it offers practical advantages for experimental operation and infrastructure development. We report on a measurement campaign in an unlined rock cavern, measuring cosmic-ray muon, neutron, and gamma fluxes, as well as radon concentration, and assessing vibrational and electromagnetic noise. We outline the planned development of the facility and the deployment of detector systems and underground instrumentation at Bedretto.

Speaker: Florian Jörg (Universität Zürich)

2026_bedretto_joerg_small_v3.pdf

12:00 Lunch

Rn Detection and Mitigation 1

Convener: Richard Schnee (South Dakota Mines)

6 Facility development for ultra-sensitive radon assaying based on electrostatic chambers at University of Windsor

Radon emanation remains a dominant background in rare-event search experiments such as neutrinoless double beta decay and dark matter detection, motivating the development of high-sensitivity assay systems for material screening and detector validation. As a noble gas, radon can outgas of detector materials and circulate within experimental volumes, making it particularly challenging to mitigate. Its short-lived progeny can plate out onto detector surfaces, introducing long-lived radioactive contamination that can mimic or obscure rare signals.

This work presents the development of a low-background radon assay facility at the University of Windsor in Canada. The system is based on electrostatic collection chambers (ESCs), which detect radon by collecting positively charged progeny onto a detector surface using an applied electric field, followed by alpha spectroscopy. Multiple detector volumes, ranging from 5 L to 15 L, are implemented to study performance and optimize sensitivity. In addition, alternative designs are being explored to improve collection efficiency, including scintillation light collection, larger-area PIN diodes, and modified detector geometries.

The facility is designed to operate multiple ESCs with low level of background inside a clean room, targeting sensitivities at the level of tens of μBq. It is intended to serve as a central radon assay platform in Canada, supporting material screening and radon detector R&D for next-generation low-background rare-event search experiments.

Speaker: Abobakr Emara (University of Windsor)

LRT2026_Windsor_Radon_Assay - AboBakr Emara.pdf

7 Background Characterization and Radon Mitigation for the PICO Dark Matter Detectors

The PICO Collaboration operates bubble chambers to search for WIMP dark matter, leveraging the excellent gamma rejection and long live fractions enabled by operating at a lower degree of superheat than the bubble chambers of the 1960s. Located at the SNOLAB underground laboratory, these detectors use fluorinated target fluids optimized for probing spin-dependent WIMP-proton interactions while operating in an ultra-low-background environment. Previous experiments, PICO-2L and PICO-60, set the world’s strongest constraints on spin-dependent WIMP-proton scattering, and the next-generation detector, PICO-40L, is now fully operational and actively collecting physics data.

This talk will provide an overview of the low-radioactivity techniques and background mitigation strategies employed within the PICO program, including radon assay and mitigation efforts, detector cleanliness protocols, and studies of low acoustic parameter background populations. We will discuss ongoing efforts to characterize detector backgrounds and environmental correlations relevant for long-duration rare-event searches. Looking ahead, PICO-500, a 250-liter chamber currently in development and expected to begin commissioning in 2026, will require further advances in low-background operation and radon control to achieve world-leading sensitivity in the search for dark matter.

Speaker: Mayank Tripathi (University of Chicago)

LRT2026_PICO_Backgrounds.pdf

8 Coating based radon barriers for future liquid xenon detectors

Despite overwhelming evidence for dark matter in our universe, its true nature remains a mystery. In the search for dark matter, detectors using liquid xenon are currently leading in sensitivity. However, these experiments are increasingly limited by intrinsic detector backgrounds, particularly the emanation of radon from detector materials. To address this challenge, a novel radon mitigation technique using surface coatings as radon barrier has been investigated. Systematic studies at the Max Planck Institut für Kernphysik have demonstrated that electrochemical plating with a 5 μm copper layer can reduce radon emanation by up to three orders of magnitude. This technique is now being scaled up to accommodate large vessel geometries using a newly developed setup.

Speaker: Sophie Armbruster

LRT_Armbruster.pdf

9 Demonstration of Efficient Radon Removal by Silver-Zeolite developed for the NEWS-G Dark Matter Experiment

We present the performance of an efficient radon trap using silver-zeolite Ag-ETS-10, measured with a spherical proportional counter filled with an argon/methane mixture. Our study compares the radon reduction capabilities of silver-zeolite and the widely used activated charcoal, both at room temperature. We demonstrate that silver-zeolite significantly outperforms activated charcoal by three orders of magnitude in radon capture. Given that radon is a major background contaminant in rare event searches, our findings highlight silver-zeolite as a highly promising adsorbent, offering compelling operational advantages for both current and future dark matter and neutrino physics experiments. This talk will describe the experiment, present the results, and highlight their broader implications for advancing low‑background experimental techniques.

Speaker: Marie-Cécile Piro (University of Alberta)

MCPiro_LRT2026.pdf

14:30 Coffee

Noble Element Based Detectors

Convener: Sean Paling (STFC)

10 Production of Radiopure Argon for the DarkSide-20k Dark Matter Experiment: The Aria and Urania Projects

Liquid argon is an excellent target for direct dark matter detection thanks to its scintillation and ionization responses combined with strong pulse-shape discrimination (PSD). The DarkSide-20k experiment, now under construction in the Gran Sasso National Laboratory (LNGS), Italy, will use a liquid argon dual-phase time projection chamber aiming at a background-free search for Weakly Interactive Massive Particles (WIMP). The use of argon sourced from the atmosphere would limit the size of such a detector by the presence of 39Ar, a 𝞫-emitter of cosmogenic origin whose activity poses significant background and pile-up concerns for a multi-tonne scale detectors. To mitigate this background the Global Argon Dark Matter Collaboration (GADMC) has developed a dedicated supply chain for the production of radiopure argon extracted from the underground, hence naturally shielded from cosmic rays and highly depleted in 39Ar.

The first phase of this program is the Urania extraction facility located in Colorado, USA. Urania is designed to obtain the underground argon (UAr) from the active gas wells. The plant is scaled to extract 121 tonnes of UAr at a purity of 99.99%, providing the raw target mass required for the forthcoming DarkSide-20k detector. To achieve ultimate detector-grade quality, the UAr is then transported to the Aria facility located in a mine shaft in Sardinia, Italy. Aria hosts a 350 meter tall cryogenic distillation column. It is designed to chemically purify the UAr to a purity exceeding 99.9999%. Together, Urania and Aria, represent a pioneering industrial scale effort in radiopure material production enabling the next generation rare-event detection technology. Additionally Aria can act as an active isotopic separation plant and has demonstrated the separation of stable argon isotopes (36Ar, 38Ar, and 40Ar). This unlocks broader enrichment opportunities for rare-event searches (using 136Xe, 76Ge) and medical diagnostics (with 18O).

Speaker: Celin Hidalgo (Gran Sasso Science Institute)

Celin_Hidalgo_LRT2026.pdf

11 An Overview of and Latest Results from the LUX-ZEPLIN Experiment

The LUX-ZEPLIN (LZ) experiment employs a 7-tonne liquid xenon time projection chamber operating 4850 feet underground at the Sanford Underground Research Facility in Lead, South Dakota, USA. LZ has achieved world-leading sensitivity to WIMP dark matter above 5 GeV/c² and reported the first >3σ evidence of coherent elastic neutrino-nucleus scattering from ⁸B solar neutrinos. The natural 8.9% abundance of ¹³⁶Xe further gives LZ sensitivity to neutrinoless double beta decay at a level competitive with current dedicated experiments. These searches span a wide range of energies and rely on careful control of backgrounds throughout. In this talk I will present LZ’s latest results. I will discuss how LZ’s subsystems were designed from the outset to minimise backgrounds, and were supported by rigorous radioassay and activity-reduction campaigns during construction. I will also review the dedicated sideband and simulation studies that are used to further constrain both radiogenic and instrumental backgrounds in searches for rare interactions.

Speaker: Ewan Fraser (University of Liverpool)

LRT2026_ LUX-ZEPLIN Results .pdf

12 Low-background Program of PandaX-20T experiment

PandaX-20T is a next-generation liquid xenon detector for rare-event searches, with stringent requirements on radiopurity and background control. We present the ongoing low-background effort for PandaX-20T, including material screening, development of new low-background materials and detector components, krypton assay, radon-related surface contamination control, and detector background estimation. Complementary techniques such as HPGe gamma spectroscopy, ICP-MS, krypton assay, and radon emanation measurements are used to characterize radioactive impurities in candidate materials and components. Surface treatment and cleaning procedures are developed to suppress radon-related contamination. The assay results are incorporated into a detailed background model and Monte Carlo simulations to evaluate gamma and neutron backgrounds from major detector subsystems. These efforts provide essential input for material selection, component development, detector optimization, and the projected background performance of PandaX-20T.

Speaker: Yue Meng (Shanghai Jiao Tong University)

PandaX-20T_mengyue.pdf

13 Background Control in DEAP-3600

DEAP‑3600, with its 3.3‑tonne target and located at SNOLAB, currently represents the leading effort within the international community in the dark‑matter direct detection in liquid argon, while construction of the next‑generation experiment, DarkSide‑20k, is underway at LNGS in Italy. By analyzing approximately three years of data, DEAP‑3600 has recently released its most up-to-date exclusion limits on Weakly Interacting Massive Particles (WIMPs), derived through a detailed Profile‑Likelihood Ratio analysis. These limits are strongly influenced by backgrounds originating from degraded alpha particles within the active argon target.

At the same time, the experiment’s large exposure and exceptionally low background levels at the MeV energy scale have enabled a broadened physics program, including the first experimental measurement of neutrino absorption in Argon‑40 using ⁸B electron neutrinos. Although never previously observed, this process is critical to the multi‑messenger astronomy and solar neutrino goals of both DUNE and DarkSide‑20k. We emphasize in this talk the techniques used to estimate (n,gamma) backgrounds to the neutrino analysis.

Detector upgrades have been ongoing since the end of the second fill run in 2020, targeting the reduction of backgrounds from shadowed alphas and dust in the liquid. These improvements are now being evaluated in the newly initiated third fill run. We also present preliminary results from
the analysis of the third‑fill data, which will inform both the effectiveness of the recent detector upgrades in suppressing backgrounds and the design of future noble‑liquid experiments

Speaker: Chris Jillings

Jillings-DEAP-LRT-2026-v5.pdf

14 K-42 mitigation studies in Ar-42-spiked liquid argon for LEGEND

The LEGEND experiment aims to detect neutrinoless double beta decay (0νββ) of Ge-76 using high-purity germanium (HPGe) detectors immersed in liquid argon (LAr). The LAr serves both as a coolant and as an active shield against background radiation. In the current phase (LEGEND-200), HPGe detectors are operated in conventional atmospheric LAr, which contains the cosmogenically activated radioactive isotope Ar-42. K-42, the beta-decaying progeny of Ar-42 (Qβ = 3.5 MeV), is a major background component of LEGEND-200. LEGEND-1000 aims to use underground LAr (UGLAr) depleted in Ar-42 to eliminate this background. In case UGLAr is unavailable, K-42 would be the dominant background at the 0νββ Q-value (2.039 MeV) due to beta-decay-induced events occurring on the surface of the HPGe detectors. These surface events must be suppressed and efficiently discriminated from 0νββ candidate events. We present K-42 suppression measurements conducted at the SCARF LAr test facility at TU-Munich using Ar-42-enriched LAr. Our study evaluates background discrimination methods, including analyzing event topologies in HPGe detectors and using scintillation light readout from LAr for suppression. Additionally, we explore enhancing suppression by surrounding the detectors with optically active barriers, such as polyethylene naphthalate (PEN) enclosures and tetraphenyl butadiene (TPB) coated nylon mini-shrouds, and present preliminary results. This research is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Excellence Cluster ORIGINS EXC 2094-39078331; SFB1258-283604770.

Speaker: Christoph Vogl (TU-Munich)

2026-09_ LRT_ 42K mitigation studies in 42Ar-spiked liquid argon for LEGEND.pdf

Crystal Scintillators

Convener: Pia Loaiza (IJCLab, CNRS/Université Paris Saclay)

15 Rare alpha decays of natural Hf isotopes

New measurements of the rare α decays of natural Hf isotopes have been performed using four Cs$_2$HfCl$_6$ crystal scintillators operated in the low-background setup of DAMA/CRYS at the Gran Sasso National Laboratory (LNGS) of INFN, Italy. The “source = detector” approach provides high sensitivity to ultra-long-lived processes by embedding the decaying nuclei directly within the detector medium. After a detailed characterization of the detector performance, including assessment of the energy calibration and pulse shape discrimination (PSD) capability, data collected over 85.23 days have been analyzed. A precise determination of the half-life of the α decay of $^{174}$Hf to the ground state of $^{170}$Yb has been obtained: T$_{1/2}=(2.95\pm0.16)\times10^{16}$ yr, improving the accuracy of previous measurements and confirming their consistency. Particular attention, in this analysis, has been devoted to the evaluation of background contributions, especially from the possible $^{147}$Sm contamination, to a proper description of the shape of observed alpha peaks, and to careful assess the systematic contributions. No statistically significant signals have been observed for the $\alpha$ decays of other naturally occurring Hf isotopes ($^{176, 177, 178, 179, 180}$Hf), and new lower limits on their half-lives in the range 10$^{19}$-10$^{20}$ yr have been established. These results confirm the potential of Cs$_2$HfCl$_6$ crystal scintillators as a detector medium for rare-event searches and provide relevant a input for nuclear structure models of the extremely long-lived $\alpha$ emitters.

Speaker: Alice Leoncini (Dipartimento di Fisica, Università di Roma “Tor Vergata”, I-00133, Rome, 8 Italy.)

leoncini_LRT26.pdf

16 High-sensitivity bolometric α screening with SURFαCE

The goal of the SURF$\alpha$CE (Silicon Underground Radiopure Finder of $\alpha$ Contamination Excesses) $\alpha$ spectrometer is to demonstrate the possibility to measure the surface radioactive contamination of the $^{232}$Th and $^{238}$U decay chains with an unprecedented sensitivity of 1 nBq/cm$^2$, a value demanded by several next-generation experiments for rare event searches. The SURF$\alpha$CE detector concept consists of an array of large-area silicon wafers instrumented as bolometers and interleaved with material samples.
Provided that a total sensitive area of 1 m$^2$, an energy resolution <10 keV FWHM, and an expected background of $10^{-8}$ counts/s/cm$^2$ in the full $\alpha$ range from 3 to 10 MeV are achieved, SURF$\alpha$CE will surpass the existing $\alpha$ detector technology by two orders of magnitude, and be capable of separately measuring parts of the $^{232}$Th and $^{238}$U chains that are out of secular equilibrium.
Thanks to the recent advancements in the technology of dilution refrigerators and bolometers, the development of such a large-area cryogenic detector dedicated to $\alpha$ screening measurements is now feasible. SURF$\alpha$CE will be located underground at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and will aim at demonstrating the feasibility, reproducibility and scalability of a bolometer for $\alpha$ measurements with a 1 nBq/cm$^2$ sensitivity, and at realizing a new-generation screening facility for surface contamination measurements.
In this talk, we will present the detector design, the results obtained from the preliminary studies of the detector response, and the plans for the realization of the full-scale setup.

Speakers: Giovanni Benato (Gran Sasso Science Institute), Dr Miryam Martinez-Vara (Gran Sasso Science Institute)

SURFACE_LRT2026.pdf

17 SABRE-North: the low radioactivity approach to dark matter annual modulation detection

The SABRE-North experiment aims to search for dark matter via the annual modulation signature, deploying an array of ultra-low-background NaI(Tl) crystals at Gran Sasso National Laboratory.
The array will be composed of nine detectors (5 kg mass each) in a Cu and PE passive shielding. The expected background rate in the energy window of interest [1,6] keV is of the order of 0.5 dru.
This challenging goal is achieved by reducing the radioactive contaminants in the NaI powder via a custom zone refining equipment and procedure, after which the crystals are grown with vertical bridgman technique, also following a radioclean procedure.
These results represent a breakthrough in the production of ultra-high radio-purity NaI(Tl) scintillators after several years of world wide efforts.
The first crystal of the physics array was completed in May 2026 in the USA and at the time of LRT will be under measurement at LNGS. We report on the methodology, tests and schedule for the completion of the array and the start of data taking.

Speaker: Krzysztof Szczepaniec

LRT2026_SABRE_ksz.pdf

Welcome Reception

Welcome Reception - drinks and nibbles

Tuesday 22 September

Experiments Background, Models and Simulations 1

Convener: Yue Meng (Shanghai Jiao Tong University)

18 Overview of current dark matter status (including main background/radiopurity challenges )

Speaker: Shawn Westerdale (University Of California Riverside)

dmoverview_ssw_22sep2026.pdf

19 DArT-in-ArDM: A Dedicated Detector for $^{39}$Ar Characterization in Underground Argon

DarkSide-20k, the next-generation dual-phase liquid argon TPC under construction at LNGS, aims to significantly advance the search for WIMP dark matter. A key requirement for reaching its sensitivity goals is the use of underground argon, strongly depleted in cosmogenic $^{39}$Ar with respect to atmospheric argon, whose natural activity would otherwise represent a major background at the multi-tonne scale.
The underground argon procurement chain includes extraction at the Urania plant in the USA and cryogenic purification at the Aria facility in Italy. Within this framework, DArT-in-ArDM represents a fundamental step, providing a direct and ultra-sensitive measurement of the residual $^{39}$Ar activity in argon samples and validating their radiopurity throughout production, purification, handling, and delivery to DarkSide-20k.
DArT is a small single-phase liquid argon detector operated inside the refurbished ArDM detector at the Canfranc Underground Laboratory, LSC, Spain. ArDM provides both the cryogenic environment for stable long-term operation and an active veto against external backgrounds, enabling $^{39}$Ar measurements in underground argon with target sensitivities at the sub-mBq/kg level.
In this talk, we present the final DArT-in-ArDM detector configuration and its performance during several months of stable operation with underground argon samples. These results build on the commissioning campaign performed with the dedicated DArT test setup, which included measurements with atmospheric and underground argon and enabled a precision measurement of the $^{39}$Ar activity in atmospheric argon.
A full simulation framework based on G4DS has been developed to model the detector response and the relevant signal and background contributions. The comparison between data and Monte Carlo, together with a dedicated sensitivity study, constrains the dominant backgrounds, assesses the ArDM veto performance, and demonstrates the capability of DArT-in-ArDM to resolve the low residual $^{39}$Ar activities expected in underground argon.
These results demonstrate the readiness of DArT-in-ArDM for the underground argon assay campaign and establish its role in the DarkSide-20k quality-control strategy, from argon procurement to final detector filling.

Speaker: Sara Tullio (INFN Cagliari)

DArTinArDM_LRT2026__ST.pdf

20 The SuperCDMS SNOLAB experiment

SuperCDMS SNOLAB is a cryogenic experiment projected to achieve world-leading sensitivity for dark matter masses below 10 GeV using semiconductor crystal detectors. The experiment employs two detector types - iZIP detectors with combined phonon and charge readout, providing excellent nuclear recoil/electron recoil discrimination, and HV detectors, which amplify phonon energy proportional to an applied external electric field to achieve lower detection thresholds. Commissioning of the full twenty-four detector payload, comprising both silicon and germanium iZIP and HV detectors, began in early 2026. Stringent background control measures have been implemented during the construction and commissioning phases of the experiment, including a suite of detailed background assays of all components and detailed tracking of cosmogenic exposures of key components. We have built a background model for the energy spectra in the detectors, utilizing the screening measurements for activity estimations. A statistical framework that fully exploits the background models in both detectors with both target materials has been established to maximize the sensitivity of the experiment. This talk presents the latest updates from the experiment, highlighting the background control and modeling efforts.

Speaker: Ziqing Hong (University of Toronto)

The SuperCDMS SNOLAB experiment - LRT2026.pdf

10:10 Coffee

Experiments Background, Models and Simulations 2

Convener: Nasim Fatemighomi

21 Overview of current 0vBB status (including main background/radiopurity challenges)

Speaker: Ruben Saakyan (UCL)

0vbb and low-radioactivity challenges

22 Background and radio-purity control for the assembly of the CUPID neutrinoless double beta decay experiment

Next generation neutrinoless double beta decay experiments aim to search for lepton number violation and the origin of neutrino mass through ton-scale experiments with ever more demanding background targets. In order to cover neutrino masses in the inverted hierarchy region, half-life sensitivities equal to or greater than 10$^{27}$ years are required. The CUPID experiment is one of the leading next generation projects in the field. It will exploit an array of 1596 cryogenic calorimeters to search for neutrinoless double beta decay of $^{100}$Mo at the LNGS laboratory. To reach this target sensitivity the understanding and control of the backgrounds at a total level of 10$^{-4}$ counts/keV/kg/yr is a key requirement. In this talk we will summarise the background sources relevant to the CUPID experiment and their correspondance to radioactive contaminations as established through detailed Geant4 MC simulations. We will present an estimation of each of the sources, subsequent radio-purity and screening requirements and a preliminary view of the CUPID asssembly strategy to prevent or minimise re-contamination.

Speakers: Benjamin Schmidt (CEA, IRFU/DPHP), Speakersboard

2026_09_22_York_CUPID_Background.pdf

23 Current Status and Latest Results from the CUORE Experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for 0νββ decay that has successfully reached the one-tonne mass scale. It is the most sensitive probe searching for lepton number violation and the Majorana nature and mass scale of neutrinos in the isotope $^{130}$Te. The detector, located at the LNGS in Italy, consists of an array of 988 TeO$_2$ crystals (750 kg) arranged in a compact cylindrical structure of 19 towers. CUORE has been collecting data continuously at ~10 mK since 2017, achieving a ~90% uptime and amassing close to 3 tonne-years of TeO$_2$ exposure. In Oct 2025 the collaboration published the most recent result of the search for 0νββ, corresponding to two tonne-year TeO$_2$ exposure. This is the largest amount of data ever acquired and analyzed with a solid state cryogenic detector, which allowed for further improvement in the CUORE sensitivity. In this talk, we will review the current status of the CUORE search for 0νββ and the CUORE science program. The large statistics also allows for one of the most detailed background reconstructions in the field and enabled a precision measurement of the $^{130}$Te 2νββ decay half-life.

Speaker: Vladyslav Berest

Berest_CUORE_General_LRD2026.pdf

24 Every Alpha, Every Decay Chain, All at Once

The SNO+ collaboration has developed a likelihood-based method to identify and tag previously inaccessible backgrounds arising from the $^{238}\mathrm{U}$ and $^{232}\mathrm{Th}$ decay chains. The method combines the time and spatial separations between candidate events with energy PDFs to evaluate correlations within radioactive decay sequences. In contrast to the sub-millisecond half-lives associated with traditional BiPo coincidence tagging, this technique enables, for the first time in SNO+, the identification of the triple-$\alpha$ sequence $^{224}\mathrm{Ra} \to {}^{220}\mathrm{Rn} \to {}^{216}\mathrm{Po}$ in the $^{232}\mathrm{Th}$ chain, as well as tagging the $^{212}\mathrm{Bi}$ $\alpha$ decay preceding the $^{208}\mathrm{Tl}$ background.

The tagging of $^{212}\mathrm{Bi}$ prior to the $^{208}\mathrm{Tl}$ decay provides a powerful tool for reducing one of the dominant backgrounds in measurements of low-energy $^{8}\mathrm{B}$ solar neutrinos. The correlations observed across different stages of the $^{232}\mathrm{Th}$ decay chain also provide an in-situ measurement of the $^{212}\mathrm{Pb}$ half-life and offer evidence for bulk scintillator motion and drift. In addition, delayed coincidence tagging techniques have been extended to isotopes above the $^{214}\mathrm{BiPo}$ coincidence in the $^{238}\mathrm{U}$ chain. SNO+ has also characterised the triple-$\alpha$ sequence $^{223}\mathrm{Ra} \to {}^{219}\mathrm{Rn} \to {}^{215}\mathrm{Po}$ in the $^{235}\mathrm{U}$ chain, providing a complementary demonstration of $\alpha$ tagging across all three naturally occurring radioactive series.

These results demonstrate the potential of extended delayed-coincidence techniques for decay-chain reconstruction, improved background characterisation, and radiopurity studies in large liquid scintillator detectors.

Speaker: Gulliver Milton (University of Oxford)

LRT_Sep_26_Every_Alpha_Every_Decay_Chain_All_at_Once.pdf

25 Neutron detection and potential for rare decay searches with low background GAGG detectors

A precise measurement of neutrons is crucial for underground experiments searching for rare events. The neutron component is often poorly known due to the lack of a scalable detector technology for the measurement of low-flux neutron spectra in a short time. Thanks to their high gadolinium content, we have demonstrated the possibility of using scintillating cerium-doped Gd$_3$Al$_2$Ga$_3$O$_{12}$ (GAGG) crystals as portable neutron detectors, as an alternative to $^3$He counters.

GAGG features a high scintillation light yield, fast time response, and the capability of particle identification via pulse-shape discrimination. In a low-background environment, the distinctive signature produced by neutron capture on gadolinium, namely a $\gamma$-ray cascade releasing around 8$\,$MeV of total energy, and the efficient particle identification provided by GAGG would yield a background-free neutron capture signal. Expoliting this signature, we have assembled a prototype neutron detector using a 100$\,$cm$^{3}$ GAGG crystal coupled to a photomultiplier tube at LNGS. Furthermore, we have investigated the possiblity of inserting GAGG wafers between NaI(Tl) detectors to maximize the detection for neutron-induced $\gamma$ photons.

Apart from neutron detection, gadolinium isotopes are also of great interest in terms of alpha decay and double beta decay investigations, which can help constrain theoretical predictions. A new measurement with the GAGG crystal is expected to significantly improve the sensitivities in these studies. For this purpose, we have designed a new experimental setup using the high-purity GAGG crystal surrounded by multiple layers of shielding to suppress environmental background. The excellent pulse-shape discrimination capability enables separation of signal-like events and backgrounds which are studied in details with delayed coincidence and Monte Carlo simulations.

In this talk, we will show the first measurement of high-energy neutron-induced $\gamma$-rays with a low background GAGG neutron detector, and then discuss further developments of the detector technology towards a new sandwich design with high detection efficiency. Finally, we present the details of background modelling and the potential to search for rare nuclear decays in the GAGG crystal.

Speaker: Yingjie Chu (GSSI)

LRT_neutron_det_final.pdf

12:40 Lunch - including conference photo

Neutron Background Mitigation

Convener: Chris Jillings

26 Review of neutron production in (alpha,n) reactions

Speaker: Roberto Santorelli (CIEMAT)

LRT2026_Santorelli.pptx

27 Development of Radiopure Gd-Doped PMMA as a Neutron-Tagging Material for Low-Background Detectors

Low background detectors, such as those used in direct dark matter searches, require high-efficient neutron veto to reject nuclear recoil backgrounds. Gadolinium-doped polymethyl methacrylate (Gd-PMMA) has emerged as a promising solid neutron tagging material, with high hydrogen content for moderating neutrons and gadolinium content for capturing thermal neutrons and exploiting subsequent emission of high-energy gamma rays. This talk introduces a novel Gd-PMMA material based on a complex compound called gadolinium methacrylate, which will be used in the DarkSide-20k experiment, a direct dark matter search experiment with liquid argon.
The Gd-PMMA will serve as both a neutron tagging material and the main structural material of the dual-phase argon Time Projection Chamber (TPC) in the DarkSide-20k detector. This design allows for the Gd-PMMA to be located as close as possible to the detector's active volume to tag any possible neutrons from intrinsic backgrounds. With liquid argon buffers on both sides of the Gd-PMMA, gamma rays released during neutron capture can be effectively detected. To maximize neutron veto efficiency, a ~1% gadolinium mass fraction with 15 cm thick Gd-PMMA surrounding the TPC's active volume is required. Radiopurity control of this material is also being studied to ensure its suitability for use in low-background experiments.

Speaker: Wang Yi (IHEP)

Gd-PMMA YW LRT2026.pdf

14:45 Coffee

Low-Background Assay Techniques 1

Convener: Isaac Arnquist (Pacific Northwest National Laboratory)

28 Characterization and application of the XIA UltraLo-1800 for ultra-low alpha measurements

Advancing the detection limits in experiments searching for rare nuclear processes, such as direct dark matter interactions and neutrinoless double beta decay, requires material selection with extremely low radioisotope content. Low-background, large-surface alpha spectrometry is one of the techniques used to measure low surface and bulk specific activities of alpha emitters. One of the most sensitive alpha spectrometers is XIA UltraLo-1800. In this detector several sources contribute to the detector background: cosmic-ray muons, decays of Rn-222 and Rn-220 in the counting gas, as well as alpha emissions originating from the anode and detector walls. To determine the instrumental background, a material producing the lowest possible alpha-particle signal is required to serve as a practical “zero” sample (a sample with virtually no alpha-particle emission). For this purpose, several candidate materials were tested: stainless steel, Teflon, etched oxygen-free copper, and electropolished oxygen-free copper. The lowest signal was observed for electropolished oxygen-free copper in a measurement lasting 76 days, with count rates of (12.6 ± 0.4) cts/d in the 1.5 – 4.5 MeV range and (6.4 ± 0.3) cts/d in the 4.5 – 6 MeV range, corresponding to the regions used for bulk and surface Po-210 analysis, respectively. Currently this material is used as a drawer base. Based on Monte Carlo simulations of detection efficiency for different materials in the full-geometry configuration, the minimum detectable surface activity (MDA) of the XIA UltraLo-1800 for the assumed relative uncertainty of 30% is 0.3 mBq/m^2, while for bulk measurements it varies between 7.4 for lead and 22.6 mBq/kg for Teflon. The corresponding detection limit (minimum activity distinguishable from the background) is 0.07 mBq/m^2 for surface measurements and 1.7 – 5.3 mBq/kg for bulk measurements. Moreover, there is a possibility to improve bulk sensitivity by reducing the detector background related to misidentified muons. Therefore an outer veto can be used. The expected improvement is at the level of 30%. Count rates for various background sources were collected over an 8 years of measurements and their analysis demonstrates the long-term stability of the detector. The XIA UltraLo-1800 is used to investigate materials for various low-background applications, including i.e. dark matter and neutrinoless double beta decay searches. As an example, measurement results for aluminium samples from the European Spallation Source will be presented, with the aim of identifying the sample with the lowest alpha emissivity. The purpose of this research is material selection for construction of a neutron detector. Among the five Al plates investigated, the lowest gross specific alpha activity, C = (30 ± 10) mBq/kg, was obtained for the nickel-coated aluminium. Details of the background studies and chosen results will be discussed.

Speaker: Milena Czubak (Jagiellonian University)

lrt2026_czubak.pdf

29 Radiopurity and cleanliness control in the XLZD rare event observatory

Xenon Time Projection Chamber (TPC) based experiments have long been among the most sensitive and successful approaches to direct dark matter detection. However, the present generation of detectors is approaching its sensitivity limits, thus, a larger detector of 60-80 tonne active liquid xenon target is envisioned as part of the XLZD collaboration. This detector is building upon the expertise of the XENON, LZ, and DARWIN collaborations with multi-science goals including dark matter detection and neutrinoless double beta decay studies. The scale‑up and expanded science reach introduce significant challenges, particularly in achieving the far stricter cleanliness and radiopurity requirements associated with such a detector. I will place particular emphasis on the radiopurity and cleanliness efforts that shape its design.
A multi‑tiered research and development programme is being pursued, including advances in high‑sensitivity background measurement and characterisation techniques, from mass spectrometry and gamma spectroscopy to radon emanation studies. In this talk, I will give an overview of these efforts, highlighting ongoing material selection studies such as cryostat investigations, developments in background measurement capabilities, and the broader strategies being pursued to meet the radiopurity and cleanliness goals of XLZD.

Speaker: Ferdos Dastgiri (University College London)

Dastgiri_LRT26_RadiopurityCleanlinessControl_Final.pdf

30 The SNOLAB Low Background Measurement Program

The Low Background Group at SNOLAB supports rare-event physics experiments through ultra-low background measurements and material assays in one of the deepest underground laboratories in the world. The group provides capabilities in high-purity germanium gamma-ray spectroscopy, ICP-MS, alpha screening, radon measurements, and neutron measurements to support experiments in dark matter, neutrino physics, and other low-background experiments. As next-generation rare-event physics experiments continue to increase in size and sensitivity, improvements in low-background assay techniques and measurement sensitivities to meet the increasing radiopurity requirements are necessary. This presentation will describe SNOLAB's low-background measurement facilities and recent developments and measurements which will help to increase the sensitivity of our low background detectors and improve detection limits. The intrinsic background measurement program of the SNOLAB underground will be discussed and plans for expanded low-background measurement capabilities and collaborative opportunities will be described.

Speaker: Ian Lawson (SNOLAB)

Ian_Lawson-LRT_2026.pdf

Mitigation of Surface Contamination

Convener: Richard Ford

31 Results of the LEGEND-200 background mitigation campaign

The search for neutrinoless double beta ($0\nu\beta\beta$) decay with $^{76}$Ge detectors tests whether neutrinos are Majorana particles and requires ultra-low background conditions, making background identification and mitigation crucial for next-generation experiments.

The LEGEND (Large Enriched Germanium Experiment for Neutrinoless $\beta\beta$ Decay) collaboration aims to improve the 3$\sigma$ half-life discovery sensitivity of $^{76}$Ge-based $0\nu\beta\beta$ experiments beyond $10^{28}$ yr through a staged approach.
The first phase, LEGEND-200, started operations at the Laboratori Nazionali del Gran Sasso in Italy in spring 2023.
During its first physics run, it operated 142 kg of high-purity germanium detectors enriched in $^{76}$Ge, immersed in instrumented liquid argon for active background suppression. LEGEND-200 achieved the lowest background index ever reached in a $^{76}$Ge $0\nu\beta\beta$ experiment, with an estimated background level of $0.5^{+0.3}_{-0.2}$ cts/(keV ton yr) in the signal region. By combining an exposure of 61.0 kg yr with data from previous experiments GERDA and MAJORANA DEMONSTRATOR, the highest half-life sensitivity to date for the search for $0\nu\beta\beta$ decay has been achieved.

In this talk, I will present the current status and performance of LEGEND-200 following an extensive cleaning, re-mounting, and background investigation and mitigation campaign aimed at reducing residual background contributions observed during the first physics run. The outcome of these studies will guide the next ton-scale phase of the experiment, LEGEND-1000, which is currently in the technical design phase and requires further improvements in low-background materials and radiation shielding.

This work is supported by the U.S. DOE and the NSF; the LANL, ORNL, and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak SRDA; the Swiss SNF; the UK STFC; the Canadian NSERC and CFI; the LNGS and SURF facilities.

Speaker: Sofia Calgaro (Universität Zürich)

Sofia_LRT26_L200.pdf

32 Characterization of $^{226}$Ra implanted sources for background mitigation and high-sensitivity $\alpha$ spectroscopy

Several next-generation experiments for rare events require a further reduction of the $^{238}$U and $^{232}$Th contamination on material surfaces with respect to what is achievable with current technologies. Such a reduction can be achieved by improved cleaning techniques or surface coating, both of which can be optimized using sources with a well-known surface contamination and/or $^{222}$Rn emanation rate.
In this talk, we will report on the characterization of 19 samples of different materials irradiated with $^{226}$Ra at the ISOLDE facility (CERN). We performed a full characterization of all samples, including the measurement of the emitted $\alpha$ spectra with a silicon PIN diode, of the $\gamma$ spectrum with a HPGe detectors, and of the $^{222}$Rn emanation with an electrostatic radon monitor and miniaturized proportional counters.
In addition, we exposed some of the irradiated samples to clean targets, yielding a very shallow $^{222}$Rn distribution which is unaffected by the nuclear recoil contribution from $^{226}$Ra decay. We measured the α spectrum with a silicon PIN diode, and the $^{222}$Rn emanation resulting from a pure diffusion process using a cryogenic radon monitor.
Finally, we simulated the primary and secondary implantation processes, as well as the recoil-induced diffusion processes using the TRIDYN software.
The availability of all these independent measurements allows us to cross-validate the different experimental techniques against each other, and the validation of the simulation against the data, guaranteeing a robust predictive power for TRIDYN-based simulations of future applications to rare-events experiments.

Speaker: Mr Lorenzo Ascenzo (University of L'Aquila)

LRT2026__Ascenzo.pdf

33 Suppressing α background in HPGe detectors for next-generation 0νββ searches

Suppressing α background in HPGe detectors for next-generation 0νββ searches

A. Biondi$^1$, G. Zuzel$^1$

1) M. Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland

High-purity germanium detectors enriched in $^{76}\mathrm{Ge}$ are among the most sensitive technologies for neutrinoless double beta decay searches, thanks to their excellent energy resolution, low intrinsic radioactivity, and use as both source and detector. In experiments such as LEGEND, pulse shape discrimination is essential to suppress background multi-site events. Surface $\alpha$ contamination is a more challenging background: $\alpha$ emitters as $^{210}\mathrm{Po}$ may produce events near the region of interest if located on the thin $p+$ detector contact. However, the number of $\alpha$ events expected in low-background experiments is too small to train dedicated classifiers, while still being relevant for the final background budget.

In this contribution, I will present a study of $\alpha$-event rejection in a BEGe-type high-purity germanium detector using pulse shape discrimination. The goal is to test whether classifiers trained on $\gamma$ calibration data can reject surface $\alpha$ events without using any dedicated training procedure.

To test this approach, the $p+$ surface of a point-contact semi-planar germanium detector was exposed to $^{209}\mathrm{Po}$ and $^{210}\mathrm{Po}$ sources deposited on thin gold foils. Two dedicated measurement campaigns were performed, yielding $1.36\times10^{5}$ and $1.87\times10^{6}$ $\alpha$ events, respectively. The classifiers were trained using selected single-site and multi-site dominated regions of a $^{228}\mathrm{Th}$ calibration spectrum. Two machine-learning methods were investigated: a multilayer perceptron and a projective likelihood classifier, with the standard $A/E$ method used as a benchmark.

Using these dedicated datasets, the response of the classifiers was evaluated. Both machine-learning methods efficiently separate single-site and multi-site $\gamma$ events while strongly reducing the $\alpha$ component. The multilayer perceptron provides the best overall performance, with a signal-like event survival greater than 80%, a background-like event survival below 20%, and an $\alpha$-rejection factor exceeding $2.71\times10^{4}$. These results demonstrate that robust pulse shape discrimination against both $\gamma$ and surface $\alpha$ events can be achieved using training information derived solely from $\gamma$-ray events.

Speaker: Alex Biondi (Jagiellonian University in Kraków)

Suppressing alpha background in HPGe AB.pdf

Poster Session

MerchantAdventurersDirections.pdf

34 Radon emanation studies at the Boulby Underground Laboratory

The Boulby Underground Screening (BUGS) Facility employs a number of techniques for material characterisation. One of these is the study of radon emanation from materials. Future large scale low background detectors will have unprecedented requirements to reduce the amount of radon emanated from materials. This poster will introduce the facility and discuss the techniques used to maximise sensitivity and throughput

Speaker: Dr Alice Hamer (STFC)

LRT 2026 Radon poster.pdf

35 From caverns to classroom - Public Engagement at Boulby Underground Laboratory

A presentation on Boulby Underground Laboratory's public engagement programme, its alignment with STFC's missions, and a touch on evaluation and local impact.

Speaker: Jonathan Gutteridge (STFC)

36 Delayed Coincidence Based Active Suppression of In-Situ Muon-Induced Isotope Backgrounds in LEGEND

The LEGEND collaboration aims to achieve an unambiguous discovery of neutrinoless double-beta decay (0νββ) using high-purity germanium (HPGe) detectors enriched in $^{76}$Ge (Q$_{ββ}$ = 2039 keV). These detectors are operated in liquid argon, which serves as both a coolant and an active shield, enabling a quasi-background-free search for 0νββ. The first phase, LEGEND-200, uses up to 200 kg of enriched HPGe detectors and is currently running in Hall A of the Laboratori Nazionali del Gran Sasso (LNGS), Italy. The next phase, LEGEND-1000, will scale the detector mass to 1000 kg, and preparation for its installation in Hall C at LNGS will begin in 2026.

To reach a 3σ discovery sensitivity for 0νββ with a half-life of 10$^{28}$ years in LEGEND-1000, the background index at Q$_{ββ}$ must be below 10$^{-5}$ cts/(keV·kg·yr). This strict limit makes previously sub-dominant backgrounds in LEGEND-200 become relevant, especially delayed decays of muon-induced isotopes. Notably, $^{77(m)}$Ge from neutron capture on $^{76}$Ge in HPGe detectors alone would exceed the background goal.

This talk presents new active suppression techniques that use delayed-coincidence tagging to identify isotope production during muon showers and delayed de-excitations from metastable daughter isotopes. These methods reduce the $^{77(m)}$Ge background to a sub-dominant 10% of the total budget, with minimal impact on the 0νββ detection efficiency (97%), supporting LNGS as a suitable site for LEGEND-1000.

This work is supported by the US DOE and NSF; the LANL, ORNL and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMFTR, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak APVV; the Swiss SNF; the UK STFC; the Canadian NSERC; the Chinese (Taiwan) MOE and NSTC; and the LNGS and SURF facilities.

Speaker: Moritz Neuberger (Technical University of Munich (TUM))

2026-09-22-Neuberger-LRT2026-York.pdf

37 In-situ Measurement of the Nuclear Recoil Background Rate in Ricochet

The Ricochet experiment measures coherent elastic neutrino-nucleus scattering (CEνNS) of reactor antineutrinos at the ILL (Grenoble, France), using germanium cryogenic calorimeters with neutron transmutation doped germanium thermistors. Dual phonon-ionization readout enables nuclear-recoil identification and efficient electron-recoil rejection. Since commissioning in 2024, Ricochet has scaled from 3 to a full 18-detector array, with the addition of detectors featuring inter-digitized electrodes providing improved surface-event rejection. A critical challenge for CEνNS detection is the irreducible background from reactor-related and cosmogenic neutrons. We present an in-situ measurement of the low-energy nuclear recoil background rate obtained during the commissioning phase.

Speaker: Valentina Novati (CNRS-LPSC)

38 Updates on Low-Background Counting at SURF

Low-Background Counting capabilities at the Sanford Underground Research Facility (SURF) are consolidated at the Black Hills Underground Campus (BHUC). Located in SURF’s Ross Campus, the BHUC is a class 1,000 cleanroom, which houses four single crystal High Purity Germanium (HPGe) counting systems and two dual HPGe crystal counting systems. While located at SURF, the BHUC counters are available to perform assays for the global underground physics community. After being temporarily located at SURF’s Davis Campus, the BHUC has now moved back into its original location and is fully operational.

Speaker: Brianna Mount (Black Hills State University)

39 Hydrofluoric acid-free Titanium etching for rare-event searches

Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radio-pure forms, titanium is a suitable material for structural elements in rare-event searches. To remove potential surface deposits, a chemical etching stage is usually undertaken. However, due to its chemical resistance, the etching of titanium conventionally requires hydrofluoric acid, which poses serious health and safety challenges, which are further exacerbated in deep underground laboratory settings. An alternative approach is proposed, which uses sulphuric acid. This talk will present tests performed with this method, including performance dependence on temperature and concentration, as well as roughness measurements performed with an optical microscope and the effect on the surface microstructure performed using a scanning electron microscope.

Speaker: Patrick Knights (University of Birmingham)

LRT_2026_etching_poster.pdf

40 Zone refining of NaI powder applied to the production of NaI(Tl) detectors for SABRE North

The SABRE North experiment at LNGS is developing ultra-high radiopurity NaI(Tl) detectors to search for dark matter.
Radio-purity, especially at the very low level of content required by DM searches, is an extremely challenging task, only partially solved so far for NaI(Tl) crystals.
To achieve its goal, SABRE North utilizes the technique called Zone Refining for NaI powder purification.
Poster presents the mathematical model, developed to describe the purification process, and comparision to the results of the Zone Refining commissioning and production runs conducted prior to crystal growth. These results can be used for production of ultra-high purity crystals for dark matter search, where low backgrounds are crucial.

Speaker: Krzysztof Szczepaniec (INFN Laboratori Nazionali del Gran Sasso)

SABRE_poster.pdf

41 Inductively Coupled Plasma Mass Spectrometry at the Boulby Underground Laboratory

The Boulby Underground Laboratory features a world-class material screening facility dedicated to the radioassay of samples for rare-event particle physics research. This poster will introduce the Inductively Coupled Plasma Mass Spectrometer (ICP-MS), one of a number of techniques employed at Boulby.

By using ion counting techniques, the ICP-MS determines the concentrations of U-238 and Th-232, providing a precise assessment of a material’s radiopurity. At Boulby we aim to push our standard detection limits to 100 parts-per-quadrillion (ppq) and even be able to push down to 10 ppq for specific materials. This information is vital for next-generation rare-event experiments, where it is imperative that radioactive backgrounds are understood to unprecedented accuracy.

Speaker: Ms Kayleigh Johnson (STFC)

ICP-MS poster LRT FINAL.pdf

42 Event Reconstruction and Detector Performance of the CROSS Experiment

The CROSS experiment, currently operating at the Canfranc Underground Laboratory (Spain), is dedicated to the search for neutrinoless double beta decay of $^{100}\mathrm{Mo}$.
CROSS employs enriched $\mathrm{Li_2MoO_4}$ and $\mathrm{TeO_2}$ crystals operated as cryogenic bolometers, together with a secondary bolometric readout of scintillation and Cherenkov light, enabling the discrimination of $\alpha$ events from $\beta/\gamma$ interactions.

In this poster, we present the event reconstruction pipeline based on the OCTOPUS software framework and report on the performance of both the $\mathrm{Li_2MoO_4}$ bolometers and the corresponding light detectors.
We describe the algorithms used to digitally trigger physical events from the continuously acquired data stream, reconstruct the relevant event parameters, correct for temperature-dependent gain fluctuations, calibrate the energy scale, identify non-physical pulses, and perform particle discrimination exploiting the different light yield of $\mathrm{Li_2MoO_4}$ scintillation signals for $\alpha$ and $\beta/\gamma$ particles.
Finally, we report on the detector performance in terms of energy and time resolution, effective light yield, and the efficiency of the various analysis stages.

Speaker: Leonardo Perna (Gran Sasso Science Institute)

Abstract_LRT (1).pdf

CROSS_Poster_LeonardoPerna.pdf

43 Laser-based production of GEM-like structures for cryogenic applications

A novel concept of GEM-like structures has recently been proposed, in which a wavelength-shifting (WLS) material is deposited inside the holes of the structure. This approach can enhance light collection efficiency in Ar-based dual-phase TPCs, addressing challenges associated with the gas–liquid interface as well as scalability limitations in future detectors.

In this work, we present recent progress in the development of WLS-enabled FAT-GEM-like structures, including the production of PMMA-based optical amplification devices using laser-based techniques, together with their initial performance assessment. This method provides a low-cost, reproducible, and low-radioactivity solution, making it well suited for large-scale production in next-generation rare-event search experiments.

Speaker: Dr Kris Haverson (Astrocent / CAMK PAN)

Poster_KHaverson_LRT_v0.pdf

44 Developing radiopurity screening with alpha spectrometry

One of the most important topics to get highly sensitive detection setups is the use of radiopure materials. To validate and classify these materials screening is required, where the usual methods are ICPMS and gamma spectrometry. However, alpha spectrometry can be used as an alternative method for large surface components. An advantage of alpha spectrometry is its sensitivity to multiple radioisotopes of the natural decay chains. It can thus measure if the secular equilibrium is broken and can also be combined with the other two methods to determine whether radioactive impurities are in the bulk or on the surface of a material.
At Dresden University of Technology, we have developed a low background alpha detector, a cylindrical Frisch-grid ionization chamber with a diameter of 30 cm. Using pulse shape discrimination, the detector can reach a very low background, measuring less than 20 events per day between 1 to 10 MeV. And in contrast to commercial alpha spectrometers, it offers a high resolution of 1.5 % at 5.5 MeV. However, the detector was previously only used for comparatively small samples. Therefore, the detection efficiency and event reconstruction of extended samples need to be studied.
In this poster I will present this experimental setup and the steps of data evaluation to mitigate background sufficiently. I show my current work on detector characterization, which focuses on efficiency determination for extended samples while keeping a high sensitivity. I will conclude with our most recent screening results on PEN foils, which shall be installed in the LEGEND experiment to mitigate argon-induced background.

Speaker: Christoph Seibt (Technische Universität Dresden)

45 Towards Low-Level Tritium Background Quantification

Tritium is a naturally occurring radioisotope in the environment due to both cosmogenic activation and the modern nuclear fuel cycle. It also remains a problematic background contribution for dark matter and solar neutrino experiments. With a Q$_{\beta}$ value of 18.6 keV, it overlaps with the WIMP search and pp and $^7$Be neutrino search regions of interest. Additionally, tritium is a problematic surface contaminate due to its absorption onto metal and plastic surfaces. Despite these issues, tritium is hard to detect and independently measure at levels relevant to rare-event physics searches. To improve the tritium detection threshold for environmental and rare-event measurements, an electrolytic enrichment capability is being created that can be used to enable ultra-low level tritium quantification. A discussion of how the enrichment can improve current detection capabilities will be presented.

Speaker: Stephanie Lyons (Pacific Northwest National Laboratory)

46 Experimental Study of Radon Solubility in Linear Alkylbenzene (LAB) for Low-Background Experiments

Radon-222 is an important source of radioactive background in low-background experiments using liquid scintillators, such as JUNO, Borexino, or KamLAND. In these large-volume detectors, the liquid scintillator, particularly Linear Alkylbenzene (LAB) in the case of JUNO, must exhibit an extremely low level of radioactivity in order to preserve the experimental performance. Produced by 226Ra contained in detector materials, or introduced through external pathways, 222Rn can migrate into the active volume and dissolve in the liquid scintillator. Once present in the target, its radioactive progeny contribute to the background and may limit the sensitivity of the experiment.
However, the available data on radon solubility in liquid scintillators remain limited. Measuring the solubility of radon in LAB is therefore essential to better understand its partitioning between the gas and liquid phases and to provide useful data for next-generation experiments.
The objective of this study is to measure the radon trapping capability of LAB through its solubility, and to investigate its evolution as a function of temperature. For this purpose, a dedicated experimental setup has been developed to evaluate the partitioning of radon between a gaseous phase and a liquid LAB phase, at atmospheric pressure and under controlled thermal conditions.
In this poster, we will present the experimental results obtained on radon solubility in LAB as a function of temperature, together with a discussion of their interpretation and relevance for future-generation low-background experiments.

Speaker: Odhongo Schephatia (CNRS)

posterLRT2026.pdf

47 Cosmogenic activation of archeological Pb-based crystals at ChipIr neutron beamline for the RES-NOVA experiment

Cosmogenic activation is a common source of radioactive background for experiments searching for rare events, such as neutrinoless double beta decay, dark matter interactions and supernova neutrino detection. Long-living isotopes, with half-lives higher than tens of days, can be particularly problematic when their decay chains produce background events in the region of interest of the experiment.

The RES-NOVA collaboration aims to deploy the first array of mK-calorimeters based on $^{\text{arch}}$PbWO$_4$ crystals at the Gran Sasso National Laboratory for the detection of galactic supernova neutrinos via coherent elastic neutrino–nucleus scattering (CE$\nu$NS). The use of archaeological lead, dated 2000 years ago, for crystal growth strongly suppresses contamination from natural radioactive chains. However, cosmogenic activation induced during above-ground crystal growth and transportation must be carefully quantified.

To assess this contribution, we irradiated samples of $^{\text{arch}}$Pb and $^{\text{arch}}$PbWO$_4$ crystals at the ChipIr neutron beam facility (ISIS, UK), whose neutron energy spectrum reproduces the atmospheric neutron flux enhanced by a factor of $10^9$. We measured the $\gamma$-ray spectra of the irradiated samples over more than one year, in order to identify the produced cosmogenic isotopes, characterize their decay chains and estimate their residual activity as a function of time. Finally, we performed data-driven Monte Carlo simulations to include the contribution from crystals cosmogenic activation into the RES-NOVA background model, a key ingredient for experimental sensitivity projections.

Speaker: Simone Quitadamo (Università degli Studi di Milano - Bicocca)

LRT2026_poster (1).pdf

48 The Twins: A dual-crystal HPGe system at the BHUC

The Black Hills Underground Campus (BHUC) on the 4850L of the Sanford Underground Research Facility (SURF) is pursuing methods to enhance its radioassay sensitivity when screening materials for future ultra-low-background experiments. This will be primarily pursued through its dual-crystal High Purity Germanium (HPGe) system, the Twins. This detector station holds dual detectors in a large inner sample chamber with the ability to reconfigure the positioning of the two detectors along one axis to accommodate large or compact sample geometries. Sensitivity will be bolstered by having additional crystal mass as well as the ability to perform coincidence/anticoincidence measurements for select applications. The dual detector system was re-installed in the BHUC in the summer of 2025. A description of the Twins system will be presented, along with its current status

Speaker: Dr Harkirat Riyat (BHSU/LZ)

A0 size LRT poster.pdf

49 Investigating the keV Energy Frontier with CUORE: Axion and Rare-Event Searches.

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first tonne-scale experiment using cryogenic calorimeters. The detector is located underground at the Laboratori Nazionali del Gran Sasso and consists of 988 TeO2 crystals operated in a dilution refrigerator at a base temperature of about 10 mK. Thanks to the large exposure, sharp energy resolution, segmented structure and radio-pure environment, CUORE provided the most sensitive exclusion limit of the neutrinoless double beta decay of 130Te.
By applying specialized data selection and noise rejection techniques to over 2 tonne·yr TeO2 exposure, we demonstrate effective event reconstruction at the keV-scale. We quantify the detector performance across the array, exploring how cryogenic conditions, vibrational isolation, and sensor properties influence sensitivity at low energies. These findings validate the use of ton-scale cryogenic calorimeters as broad-range rare event detectors, spanning from the keV to the MeV scale. In this contribution, we present recently published and new results on CUORE's potential for keV-scale energy physics including searches for dark matter interactions and rare nuclear decays such as the unobserved 123Te EC.

Speaker: Vladyslav Berest

50 Optimising GEANT4 event biasing for underground rare-event searches

Rare-event search experiments are continuously extending their sensitivities to unprecedented levels. Achieving these feats requires increasingly small backgrounds, partly as a result of improved shielding schemes and deep underground laboratories that can suppress external backgrounds by several orders of magnitude. Detailed detector and shielding simulations are required to attain a good understanding of experimental backgrounds, and the achieved sensitivity. With backgrounds now frequently below 0.01 counts per kg of target per keVee of energy, said simulations require increasingly more computing resources. Event biasing is often applied to mitigate this issue, particularly in shielding simulations, yet there is a lack of studies providing systematic guidance on how to best optimise biasing techniques for statistical precision and CPU-time, limiting the obtained benefit. Such an optimisation study for the importance-splitting biasing technique implemented in GEANT4 will be discussed, focused on balancing statistical precision with simulation CPU-time. This may also result in reduced computing-related CO2$_{\rm e}$ emissions, which is also discussed.

Speaker: Dr Lachlan Milligan (University of Birmingham)

LRT2026PosterBiasing_LMPDF.pdf

51 Results from underground operation of SABRE South at SUPL

The SABRE South experiment at the Stawell Underground Physics Laboratory (SUPL) is currently in the construction and commissioning phase, preparing to become Australia's first deep-underground dark matter direct detection experiment. Employing an array of ultra-pure NaI(Tl) crystals, SABRE South aims to independently test the annual modulation signal reported by DAMA/LIBRA. We present an update on the status of construction and commissioning at SUPL, progress on the production of high purity astrograde crystals produced at the Shanghai Institute of Ceramics, Chinese Academy of Sciences (SICCAS), and associated assay results. We report results from underground operation at SUPL, including measurements of the cosmic-ray muon flux. Finally, we present Pyrate, the dedicated software framework developed for the experiment, which handles online and offline PMT waveform processing and analysis.

Speaker: Sai Pemmaraju (University of Melbourne)

52 Radioactivities of AMoRE Crystals

The AMoRE experiment searches for neutrinoless double beta decay of $^{100}$Mo using cryogenic molybdate crystals operated at millikelvin temperatures. A detailed understanding and reduction of radioactive backgrounds near the region of interest is essential for improving the experimental sensitivity. In particular, radioactive contamination on or near the crystal surfaces can produce degraded alpha events that may contribute to the background continuum.
In this work, we study the radioactivities of AMoRE crystals using alpha events observed in the AMoRE-I data. Alpha-induced signals provide a powerful tool for identifying internal and surface contaminations from natural decay chains such as $^{238}$U and $^{232}$Th. In addition, sequential alpha decays with characteristic energies and time correlations can be used to tag specific decay-chain segments and to distinguish bulk contamination from surface-related activity. By analyzing the energy spectra, event topology, and delayed-coincidence signatures of alpha events, we estimate the activities of relevant radionuclides in the detector crystals.
We present preliminary results on the radioactivity levels of AMoRE crystals and discuss their implications for background modeling and future background reduction strategies in AMoRE.

Speaker: Bijaya Sharma (INSTITUTE FOR BASIC SCIENCE, UST)

Bijaya_LRT2026workshop_abstract.pdf

53 Response of a nitrogen-filled spherical proportional counter to MeV-energy neutrons

Neutron spectroscopy is an invaluable tool for a wide range of scientific and industrial applications, including underground dark matter searches. Neutron-induced backgrounds originating from cosmic-ray muons and cavern radioactivity can mimic the expected dark matter signal and therefore constitute a major source of background in rare-event experiments. However, current neutron detection techniques suffer from several limitations, making precise measurements particularly challenging. A promising approach to neutron spectroscopy is the use of a nitrogen-filled Spherical Proportional Counter (SPC), exploiting the $^{14}N(n,α) ^{11}B$ and $^{14}N(n,p)^{14}C$ reactions. Measurements with mono-energetic neutrons were performed for the first time at the 5.5 MV Tandem accelerator of the National Centre for Scientific Research “Demokritos”, Athens, using a 30 cm in diameter nitrogen-filled spherical proportional counter equipped with an 11-anode ACHINOS multi-anode sensor with individual anode read-out. The detector response at an operating pressure of 1 bar to mono-energetic neutrons of $E_n$ = 0.2, 1.0, 2.5 and 3.75 MeV produced via the $^{7}Li(p, n)^{7}Be$ reaction will be presented and compared with result of a dedicated simulation framework.

Speakers: Ioannis Manthos, Manthos (University of Hamburg, Institute for Experimental Physics, Hamburg, 22761, Germany)

LRTposter.pdf

54 The LUX-ZEPLIN Outer Detector: Performance and Machine Learning Algorithms for Position Reconstruction

The LUX-ZEPLIN (LZ) dark matter direct detection experiment employs a 7-tonne dual phase xenon time projection chamber (TPC), with the primary goal to detect nuclear recoils from Weakly Interacting Massive Particles (WIMPs). The neutron background must be minimised in LZ, as neutron single scatters produce nuclear recoil signals which are indistinguishable from WIMP interactions. The LZ Outer Detector (OD) plays a crucial role in vetoing neutrons through the detection of coincident signals between the TPC and OD. The OD, which surrounds the TPC, consists of 17-tonnes of radiopure gadolinium-loaded liquid scintillator distributed across 10 segmented acrylic tanks, with further shielding provided by the encasing ultra-pure water tank. Signals in the OD are detected by 120 inward-facing Hamamatsu R5912 photomultiplier tubes. Position reconstruction in the OD could help improve constraints on the neutron background rate and reduce the detector dead-time by ensuring that coincident neutron signals are spatially correlated with TPC signals. To this effect, convolutional neural networks (CNN) have been developed for position reconstruction in the LZ OD. This talk will provide an overview of the OD and its performance, and the development of CNN algorithms for improved OD position reconstruction

Speaker: Tea Hall (University of Liverpool)

LRT2026_TeaHall_ODML_V4.pdf

LRT2026_TeaHall_ODML_V4.pptx

55 External Gamma Background and Shielding Study for Cryogenic Bolometer 0νββ Experiments at CJPL

We study environmental gamma-ray backgrounds relevant to cryogenic bolometer experiments at the China Jinping Underground Laboratory (CJPL). A CZT detector was used to measure the underground gamma spectrum, and a Geant4 model was developed to simulate its response. The deconvolution method is applied to reconstruct the incident gamma flux.
The reconstructed flux is then used as an input for Geant4 simulations of a cryogenic bolometer detector to evaluate background event rates. We further study shielding designs based on lead and copper to reduce external gamma backgrounds, and investigate pile-up effects arising from the slow response of cryogenic bolometers.
This work provides input for background modeling and shielding optimization for future low-background experiments at CJPL.

Speaker: Fang Xie (Fudan University)

56 Latest Development of the Specialty Ultra-low Background Detector Manufacturing

Mirion Technologies has developed detectors to cope with the requirements
of low radioactivity measurement: the Specialty Ultra Low Background (S-ULB) detectors. For the construction of a S-ULB detector, each element that enters its composition must be selected carefully to reduce as much as possible the intrinsic radioactivity of the detector itself. The S-ULB detectors achieved a consistent intrinsic radioactivity of the order of a few hundred counts per day and per kg of Ge.

Specific needs for low radioactivity measurements are addressed. For example, the detector orientation of the BEGe unit can be changed and modified to have two detectors facing each other. This configuration increases the solid angle coverage by a factor and provides optimized efficiency for large sample measurement. Increase of the crystal diameter of the BEGe detector up to 105 mm leads to a large surface ideal for large sample measurements. The ratio of active volume over internal radioactivity becomes even better. For measurements of small volume samples, the SAGe™ Well detector with a well diameter of 21 mm provides close to 4PI solid angle coverage. Each detector can have a specific design, low radioactivity material, with similar standard HPGe energy resolution: 600 eV at 122 keV and 1.7 keV at 1332 keV for a 1.2 kg BEGe detector. For low radioactivity techniques, this led to better minimum detection activity or reduction of measurement time. The advantages and the performance of the latest developments of the Mirion S-ULB detectors are presented here.

Speaker: Damian Ralet (Mirion Technologies)

57 Status of Cryogenic Bolometer R&D for Neutrinoless Double-Beta Decay Searches at CJPL

The search for neutrinoless double-beta decay (0νββ) is a key approach to probe the Majorana nature of neutrinos and lepton-number violation beyond the Standard Model. Cryogenic scintillating bolometers, offering excellent energy resolution and powerful particle identification, are a leading technology for next-generation 0νββ experiments.

We report the status of cryogenic bolometer R&D for 0νββ searches at the China Jinping Underground Laboratory (CJPL). The program focuses on the development and characterization of scintillating bolometer modules based on lithium molybdate crystals operated in a dual heat–light readout configuration. Recent activities include the construction and commissioning of prototype detector setups, optimization of detector assembly and operation procedures, and laboratory performance studies using ground-based measurements. Calibration strategies employing heater pulsing and radioactive sources have been developed to establish energy response and detector stability. In parallel, simulation studies are being performed to evaluate detector response and background conditions relevant to future large-scale implementations.

These R&D efforts are carried out within the broader international effort toward next-generation cryogenic bolometer experiments for 0νββ searches, and provide important input for the optimization and development of future detectors.

Speaker: Fang Xie (Fudan University)

58 The BUGS facility at Boulby

The Boulby Underground Screening (BUGS) facility at Boulby has been operational since 2014. In the intervening 12 years, the facility has characterised materials from a number of low background experiments. This talk will discuss each of the techniques employed in BUGS and our plans for development as the Boulby Underground Laboratory expands.

Speaker: Ms Beth Green (STFC)

59 Accelerated 210 Pb Radon Plate-out for Detector Background Calibration in SuperCDMS

Near-detector surface contamination from 210 Pb produces a persistent background for the SuperCDMS experiment due to subsequent beta decays and 206 Pb nuclear recoils from 210 Po alpha decays. Characterizing the energy and position distribution of these near-surface backgrounds through a calibration campaign is essential for informing fiducial-volume cuts and determining their effectiveness. This presentation details the constraints and fabrication methods required to produce an optimal 210 Pb calibration source. The source activity must be designed with a decay rate low enough to minimize detector event pile-up but high enough to exceed background rates at the test facility to produce statistically significant results. To meet activity requirements at the time of deployment, our group uses an accelerated electrostatic radon plate-out process. We will present the constraints driving our target activity calculations alongside the design and implementation of the source fabrication apparatus.

Speaker: Nevena Cail (SDSM&T)

60 The way to zero background search with LEGEND-1000

The LEGEND project (Large Enriched Germanium Experiment for Neutrinoless ββ Decay) aims to detect neutrinoless double beta decay of 76Ge using enriched high-purity germanium detectors immersed in liquid argon. The LEGEND collaboration is currently operating the LEGEND-200 detector in the Underground Gran Sasso Laboratory (LNGS), instrumented with around 130 kg of germanium detectors immersed in atmospheric liquid argon. A second phase is foreseen and it will operate the LEGEND-1000 detector currently under technical design phase; it will use 1000 kg of enriched high-purity germanium detectors arranged in strings, deployed in underground liquid Argon, depleted in Ar-39. The background Index goal for LEGEND-100 at Qββ is 10^-5 cts/(keV kg yr) and the half-live sensitivity for a discovery of 0νββ of 76Ge is > 10^28 yr after 10 yr live time. This talk will review the background suppression techniques that will be employed to reach this goal. This work is supported by the U.S. DOE, and the NSF, the LANL, ORNL and LBNL LDRD programs; the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak RDA; the Swiss SNF; the UK STFC; the Canadian NSERC and CFI; the LNGS and SURF facilities.

Speaker: Riccardo Biondi (Gran Sasso Science Institute)

Biondi - LRT 2026 - The way to zero background search with LEGEND-1000.pdf

61 Radon-Induced 210Po Surface Contamination and Cleaning Studies on Copper for AMoRE-II

Rare-event search experiments such as AMoRE (Advanced Mo-based Rare process Experiment) require ultra-low background levels and therefore operate in underground laboratories. In such environments, where ventilation is limited, ²²²Rn progeny accumulate on detector surfaces and contribute to the experimental backgrounds. The AMoRE-II, the phase-2 of the AMoRE program, is located underground at Yemilab (²²²Rn ~205 Bq/m³), with various metal components — Cu, Pb, SS, and Fe — stored prior to deployment. Past cases of elevated surface α activity on Pb components exposed to Rn-rich environments, and the subsequent removal of ²¹⁰Po contamination via HNO₃ cleaning, indicate that quantitative characterization of Rn-induced surface contamination and the validation of acid cleaning protocols for metal components are required as inputs to the AMoRE-II background budget.
To this end, we apply a three-step protocol to Cu 4×4 cm² samples prepared identically to the AMoRE-II cans: (i) surface sanding, (ii) ²²²Rn exposure, and (iii) standard acid cleaning. Surface α activity is measured after each step using a 12 cm² Si α counter with a background of 0.05 count/hr/cm². The ²²²Rn exposure condition is set using the Jacobi deposition model to be equivalent to 49 days of exposure in the Yemilab environment, reproducing the actual ²¹⁰Po accumulation behavior on an accelerated timescale.

Sanding reduced the surface α activity to approximately one-third of its initial level. Over ~100 days of follow-up measurements after Rn exposure, we observed a time-dependent increase in the 5.3 MeV peak rate, attributed to ²¹⁰Po ingrowth from ²¹⁰Pb implanted on the surface. In this poster, we report the surface accumulation rate and saturation surface activity of ²¹⁰Po extracted from the ingrowth fit, together with the post-cleaning saturation surface activity, the ²¹⁰Po removal efficiency, and the surface contamination depth profile.

These results provide direct inputs to the AMoRE-II background simulation and serve to validate the acid cleaning protocol for metal components. Extension of the same protocol to Pb, SS, and Fe samples is planned as a follow-up study.

Speaker: Daehoon Ha

260922_LRT_Status of radon exposure tests on Metal surface for AMoRE.pdf

62 Status and prospects of the DarkSide-20k experiment

DarkSide‑20k is the next‑generation, multi‑tonne dark matter experiment within the Global Argon Dark Matter Collaboration. The core of the experiment, primarily designed for WIMP direct detection, consists of a dual‑phase time projection chamber (TPC) filled with about 50 tonnes of liquid argon extracted from underground (UAr) at URANIA (Colorado) and chemically distilled at ARIA (Italy), with its radioactivity assayed in DArT (Spain).
The TPC is inserted into an Inner Veto (32 tonnes of UAr) for active neutron rejection and, surrounding the full inner detector, a bath of 650 tonnes of atmospheric liquid argon. All detectors will be instrumented with low-noise and low radioactivity silicon photomultipliers developed by Fondazione Bruno Kessler, all integrated as Photon Detection Units (PDUs), making DarkSide-20k the first experiment in astroparticle physics to deploy semiconductor‑based photosensors at these scales, with an ongoing testing and characterization chain involving multiple institutions world-wide.
The careful selection of detector materials and cleaning procedures of the inner detector, the years‑long optimization of the read-out system, and the underground argon supply chain developed over the past decade are now converging, as the experiment construction proceeds at the Laboratori Nazionali del Gran Sasso (LNGS, Italy), promising for its world‑leading sensitivity to WIMPs, potentially down to the neutrino fog.

Speaker: Michela Lai (Queen's University)

63 Results and perspectives of the ACCESS project

Current constraints on the Majorana neutrino mass are strongly affected by uncertainties in the nuclear matrix element calculations underlying neutrinoless double-beta decay. A key step toward improving nuclear calculations within a data-driven framework is validating their predictions through challenging nuclear processes, such as highly forbidden $\beta$-decays. The ACCESS (Array of Cryogenic Calorimeters for Rare Event Search) project aims to establish a novel experimental approach using cryogenic calorimeters for high-precision studies of forbidden $\beta$-decays. By operating a pilot array of natural and doped crystals that embed $\beta$-emitting radionuclides, ACCESS enables a unified and complementary investigation of both naturally occurring isotopes (such as $^{113}Cd$ and $^{115}In$) and synthetic isotopes (such as $^{99}Tc$ and $^{36}Cl$). This technique allows the simultaneous measurement of decay half-lives and spectral shapes with excellent energy resolution and efficiency. In this contribution, after a brief overview of recent advances in the field, we present a new low-threshold measurement of the fourth-forbidden $\beta$-decay of $^{115}In$, obtained from the combined analysis of two cryogenic calorimeters with indium iodide and indium oxide absorbers. We further discuss two complementary experimental approaches for the study of $^{99}Tc$ and potentially several other isotopes, based respectively on neutron-activated crystals and on tellurium dioxide slabs with a deposited $^{99}Tc$ source.

Speaker: Riccardo Elleboro (INFN/Univaq)

Poster ACCESS LRT2026.pdf

64 remage: a modern simulation framework for low-background physics experiments

remage is a Geant4-based simulation framework developed within the LEGEND collaboration to meet the needs of germanium- and liquid-argon-based low-background experiments, and is used for both the main LEGEND experiment and its associated gamma-ray screening stations. It is designed to remove the usual friction of Monte Carlo work in this field: minimal setup to reach a first working simulation, straightforward geometry registration and benchmarking, easy-to-analyze output, and advanced tools for event vertex confinement and custom vertex input. Built with performance in mind for the very low detection efficiencies typical of background simulations, remage is complemented by Python-based tools for building detector geometries, and scales from simple gamma-counting setups to detailed full-array models. We describe its design, backed by an extensive validation suite and thorough documentation, show example applications to LEGEND physics analyses, and discuss its potential for adoption beyond LEGEND.

Speaker: Luigi Pertoldi (TU Munchen)

65 A radioassay and simulation database for XLZD

The next-generation liquid xenon detectors, such as XLZD, will operate at an unprecedented scale, increasing the target xenon mass by an order of magnitude relative to current-generation experiments such as LZ. New sensitivity requirements combined with the scale-up in detector mass demand significantly stricter radiopurity requirements and far more rigorous tracking and analysis of background contributions from detector construction materials. This poster will present the XLZD material screening database and background budget calculator – a centralised system designed to manage the full scope of radiopurity screening data. The database stores material properties and assay results, tracks sample locations and states for radon plate-out calculations, and links detector components to compressed simulations for background activity scaling. We demonstrate the full pipeline using existing assay results and preliminary XLZD simulations, quantifying the contribution of each component to the total background budget. The system is live on King’s College London servers and, through an intuitive interface, acts as a searchable database for assay results and sample status, directly informing procurement and design decisions. Together, these tools give XLZD the logistical and analytical infrastructure needed to meet the background requirements of the next generation of rare event searches.

Speaker: Bram Miles (Univeristy College London)

XLZDDatabasePosterDraft5.pdf

66 Shallow underground backgrounds and the Underground Counting Facility at Savannah River National Laboratory

Shallow underground laboratories (less than 100 meters underground) are more accessible and well suited for a wide variety of measurements than their deep underground counterparts. While backgrounds in deep underground laboratories are extensively studied for large, ultra-low background experiments —resulting in comprehensive background models— less literature is available on background models for shallow underground laboratories.
This work presents a study of backgrounds in the Underground Counting Facility (UCF) at Savannah River National Laboratory (SRNL), a shallow underground laboratory for ultra-sensitive radiation detection. Simulations developed to assess the background contribution to ultra-sensitive radiation detectors in the UCF are compared to measurements and are used to evaluate the impact of the facility’s unique design choices on the background. Studies presented here are broadly applicable to shallow underground laboratories.

Speaker: John Armstrong (Savannah River National Laboratory)

Wednesday 23 September

Rn Detection and Mitigation 2

Convener: Jim Dobson (King's College London)

67 Radon-222 Screening Capability and Research at SNOLAB

Radon-222 is a limiting background in many leading dark matter and low-energy neutrino experiments. At SNOLAB, we operate several radon assay systems dedicated to material screening and to measuring radon concentrations in N₂ gas systems and ultra-pure water. This talk will describe these instruments and their capabilities. In addition, it will highlight a recent development aimed at improving our N₂ gas assay sensitivity and expanding our radon measurement capabilities

Speaker: Nasim Fatemighomi

LRT2026NasimFatemighomi.pdf

68 Measurements of Radon Diffusion and Emanation from Titanium

The LUX-ZEPLIN (LZ) Ti cryostat, despite having record low levels of many reported radioactive contaminants, shows a surprisingly high level of radon emanation. Possible explanations include ineffective acid etching of surface contamination, significant surface contamination added after the etching, or surprisingly high diffusion of radon in Ti. Measurements to determine the cause and help ensure low radon emanation from Ti in the future will be discussed. Upper limits on radon diffusion through Ti are determined using a setup with Ti foil. Radon emanation is being measured using cleaned Ti from the same batch as used for the LZ cryostat, and from additional Ti discs both before and after acid etching, with multiple measurements providing information on the fraction of radon emanation due to recoils vs. diffusion.

Speaker: Prof. Richard W Schnee (SDSM&T)

69 Updates on the International Radon Network

The International Radon Network was recently established to improve coordination between laboratories and collaborations working on radon detection, measurement, and mitigation has gained support from researchers across the dark matter, neutrinoless double beta decay, and underground physics communities, alongside growing interest in industrial applications and research translation. This presentation provides an overview of recent radon advances, together with updates on the network's objectives. These include: (1) the development of an open access database of radon-related measurements and resources, (2) the standardisation of performance metrics through coordinated intercomparison campaigns, and (3) ongoing technical collaboration through a community review paper on emanation facilities and the scheduled Radon Zero Backgrounds Workshop. Together, these activities are helping to build a coordinated international radon community to support the next generation of rare-event physics experiments.

Speaker: Dr Robert Renz Marcelo Gregorio (Australian National University)

70 Study and development of new radon adsorbents - Update of the IRENE Project

Radon is one of the most significant sources of radioactive background in low-energy and ultra-rare event particle and astroparticle physics experiments, such as neutrinoless double-beta decay searches and direct dark matter detection.
Future-generation experiments will require radon concentrations at the level of only a few atoms per cubic meter or per kilogram. Achieving such extremely low concentrations demands the use of highly efficient radon adsorbents.
Several silver-exchanged zeolites have demonstrated radon adsorption capacities more than two orders of magnitude greater than those of the best carbon-based adsorbents reported to date. While these materials exhibit exceptional performance, the mechanisms underlying their adsorption properties remain poorly understood. For future experiments, it is essential to develop a thorough understanding of these materials and establish controlled production processes that ensure both outstanding adsorption performance and ultra-low intrinsic radium contamination.
In this context, the IRENE project, launched in February 2024, brings together CPPM and four laboratories specializing in physical chemistry and materials science. Its objective is to understand, optimize, and develop innovative materials for extreme radon adsorption, with a particular focus on xenon-based applications.
In this presentation, we will discuss recent progress in understanding radon adsorption mechanisms and present preliminary results obtained with newly developed materials.

Speaker: Hichem Tedjditi

260923_LRT_IRENE.pdf

71 Diffusion of 210Pb and 210Po in Nylon

Radon and its progeny represent a significant source of background in rare-event physics experiments owing to their continuous production within the natural uranium decay chain. To investigate the diffusion of radon daughters into detector materials, we developed a dedicated experimental setup comprising a controlled radon source, a high-electric-field vacuum chamber, and a thin Nylon-6 film. Nylon-6 was chosen as the initial test material because of its extensive use in low-background detectors, with future studies planned for a broader range of polymers. Using this system, we performed controlled measurements of the diffusion behavior of 210Pb and 210Po under varying relative humidity conditions. Significant humidity-dependent diffusion was observed, with markedly different behavior at 40% and 95% relative humidity. These findings indicate that elevated humidity can enhance the migration of radon progeny into detector materials, emphasizing the need for careful environmental control to minimize backgrounds in ultra-low-background experiments.

Speaker: Pushpa Adhikari

72 Testing radon mitigating surface coatings in Xenoscope - a 2.6 meter long liquid xenon TPC

Large liquid xenon experiments have become one of the leading detector technologies applied in rare event searches, such as direct dark matter detection or the search for the neutrinoless double beta decay.
Significant background sources to these searches arise from progeny isotopes of the radioactive noble gas $^{222}$Rn, which can emanate from detector surfaces. In particular for the next generation detectors such as XLZD, additional radon mitigation methods will be required to reach their designed sensitivity goals.
A novel radon mitigation technique based on electrochemically deposited surface coatings has recently been developed at the Max-Planck-Institut für Kernphysik (MPIK) in Heidelberg, achieving a thousandfold reduction in radon emanation from stainless steel samples. This work aims to apply and validate this method in a large-scale liquid xenon detector for the first time, while assessing its compatibility with the ultra-high purity requirements of LXe detectors and evaluating its long-term stability under cryogenic operating conditions. The coating will be performed in collaboration with MPIK and will be validated in Xenoscope, a 2.6-m-long dual-phase TPC operated at the University of Zurich, which provides a representative environment for large-scale LXe detectors.
In this contribution, recent results from Xenoscope will be presented, alongside with the status and plans of applying surface coatings to the detector.

Speaker: Margherita Noia (University of Zurich)

MNoia_LRT_2026.pdf

11:00 Coffee

Special Topic - Celebrating the History of LRT

73 History Of LRT to celebrate edition 10

Speaker: Richard Ford

Special Topic - Roundtable Discussion

13:00 Lunch

Conference Dinner

Thursday 24 September

Production of Radiopure Materials & Additive Manufacturing 1

74 Review of Cosmogenic Backgrounds & Material Activation

Speaker: Susana Cebrian (Universidad de Zaragoza)

LRT2026_cosmogenics.pdf

75 CUPID Crystal Validation Run: A Systematic Framework for LMO Crystal Performance and Radiopurity Assessment

CUPID (CUORE Upgrade with Particle IDentification) is a next-generation experiment aiming to search for $0\nu\beta\beta$ decay of $^{100}$Mo and to probe the inverted-hierarchy region of neutrino masses. CUPID is designed to minimize background for $0\nu\beta\beta$ decay by exploiting the high Q-value of $^{100}$Mo, which sets the region of interest above almost the entirety of the natural $\beta/\gamma$ background, and by implementing particle identification via a dual readout of heat and scintillation light to suppress the $\alpha$ background. In particular, CUPID will operate 1596 Li$_2^{\mathrm{enr}}$MoO$_4$ scintillating crystals (LMO), each coupled with a pair of Ge light detectors (LDs). Both the calorimetric and scintillating properties of LMO crystals, as well as their ultra-high surface and bulk radiopurity, are crucial for achieving the target sensitivity of CUPID. The task of growing, cutting and polishing of LMO crystals has been assigned to the Shanghai Institute for Ceramic Materials (SICCAS). However, the lack of industrial-scale expertise in the production of LMO has required SICCAS to develop a robust and reliable production process, starting from the synthesis of LMO powder up to the final polishing of the crystal surfaces.
To monitor the crystal quality during the R&D and the upcoming mass-production phase, the CUPID collaboration has developed an extensive multi-technique protocol for crystal-quality assessment, at the heart of which lie the CUPID Crystal Validation Runs (CCVRs).
The latter are cryogenic measurements of various crystals produced by SICCAS, performed by operating LMOs and LDs as bolometers in a standardized detector assembly to assess their performance and radioactive contamination levels. In comparison to other techniques implemented for radiopurity assessment of CUPID materials ($\gamma$-spectroscopy, ICP-MS, and NAA), the bolometric measurement is the only technique capable of combining both sensitivity to every portion of the natural radioactive chains, despite possible secular-equilibrium breaking, and the possibility of working with reduced array sizes for the samples or limited measurement times, making it the cornerstone of the low-radioactivity assay developed to reach the ultra-low contamination targets of CUPID.
This talk will present the results of the CCVRs performed during the R&D phase of LMO crystal growth, together with the optimization work already completed and still ongoing to enable the transition to the mass-production phase of the CUPID experiment.

Speaker: Tommaso Bradanini (INFN Milano-Bicocca)

CUPID-Tommaso_Bradanini_LRT_Abstract.pdf

TBradanini_Cupid Crystal Validation Runs_ a Systematic Framework for LMO Crystals Performance and Radiopurity Assessment.pdf

76 Material procurement, purification, and assay for low-background experiments at CUP

At the Center for Underground Physics (CUP) at the Institute for Basic Science in South Korea there are two major scientific directions in the field of low-background physics. The AMoRE experiment is searching for the neutrinoless double beta decay of the Mo-100 isotope using molybdate-based bolometric crystals, and the COSINE experiment aims to scrutinize the annual modulation signals observed by the DAMA/LIBRA experiment using 200 kg of NaI(Tl) crystals with extremely low intrinsic background levels.

The second phase of AMoRE experiment, AMoRE-II, uses an array of 360 ultra-pure lithium molybdate Li2100MoO4 (LMO) crystals operated as cryogenic calorimeters. The crystals have a cylindrical shape with dimensions (D × L) of 5 × 5 cm and 6 × 6 cm with a target intrinsic radiopurity to be below 10 µBq/kg. After several years of mass purification of initial materials and mass production of crystals, crystal growth was successfully completed using the Czochralski pulling technique with CUP-purified precursor materials. In parallel with crystal production and initial material purification, the extraction and re-purification methods for Mo-100 were developed at CUP to recycle the expensive Mo-100 isotope and maximize the overall material balance. Throughout the production process, we tested each batch of purified products and each produced crystal using ICP-MS and/or HPGe to ensure radiopurity.

Moving towards COSINE-200 stage, we have developed and installed an in-house mass-scale NaI powder purification facility to have an initial NaI material for crystal production with a total K level below 20 ppb and 210Pb below 0.5 mBq/kg. At the moment, we have produced and accumulated about 400 kg of the product with such purity. Currently, CUP-produced NaI powder has been confirmed to be a good material for synthesizing ultra-pure NaI crystals using the Kyropoulos and Bridgman methods. However, we are facing an issue with the availability of the source material for purification, as its production has been discontinued and there is no suitable substitute of sufficient purity.

In this report, we summarize our progress in material recycling and assays for various materials at CUP, including ICP-MS assays of LMO crystals produced from different initial materials using various crystallization methods, the purity of the recycled materials used, and a material balance. Recent developments and improvements in NaI production will be given, along with an update on the newly produced NaI crystals at CUP.

Speaker: Olga Gileva (Center for Underground Physics, IBS)

LRT2026_Abstract_Olga .docx

10:10 Coffee

Production of Radiopure Materials & Additive Manufacturing 2

Convener: Jodi Cooley (SNOLAB)

77 Improvement and assessment of the radiopurity of Micromegas readout planes

Micromesh Gas Structures (Micromegas) as readout of gaseous Time Projection Chambers (TPCs) are being considered in experiments investigating rare phenomena, like the nuclear double beta decay, solar axion detection and low-mass dark matter interactions, due to their good performance on spatial and energy resolution and operation stability. In addition, as they are potentially made mainly of radiopure materials like copper and kapton, they are appropriate for ultra-low background conditions. After a promising first study of the radiopurity of Micromegas readout planes, here results after dedicated development at CERN obtained from new radioassays, performed at the Canfranc Underground Laboratory combining different techniques, are presented. Activity of the isotopes in the lower parts of the 238U and 232Th natural chains has been constrained by analyzing the BiPo sequences using the BiPo-3 detector to be <0.064 and <0.016 muBq/cm2 respectively, while a lowest 40K content of 0.102+-0.030 muBq/cm2 has been determined by gamma spectroscopy using a HPGe detector; the latter value implies a reduction of a factor ~34 with respect to the 40K activity quantified in the first analyzed sample. These results confirm the suitability of the use of Micromegas as extremely radiopure readouts for rare event searches.

Speaker: Susana Cebrian (Universidad de Zaragoza)

LRT2026_Cebrian.pdf

78 Designing ultra-radiopure, high-strength copper-alloys for future rare-event searches

The quest to directly detect dark matter and unravel the nature of neutrinos has driven the development of experimental techniques with unprecedented sensitivity, placing extreme demands on detector-material-induced backgrounds. As a result, the choice of construction materials, particularly those in direct contact with the target medium, has become a critical limiting factor. Electroformed copper, thanks to its exceptional radiopurity, is the material of choice for low-background experiments. However, its limited mechanical strength and ductility restrict its application in large-scale, high-pressure, or load-bearing components.

A materials design perspective to address this challenge is proposed. The recent advances in the synthesis and design optimisation of high-strength, radiopure copper-based alloys, specifically Cu-Cr and Cu-Cr-Ti, using computational thermodynamics will be presented. By combining electrodeposition techniques with CALPHAD-based modelling, rapid predictive design of alloy compositions and thermal processing is enabled, allowing us to navigate the trade-offs between radiopurity, mechanical strength, and manufacturability. The physics impact of such materials breakthroughs will be illustrated through case studies of next-generation experiments.

Speaker: Dimitra Spathara (University of Birmingham)

79 Electroformed Cu-Cr Alloys

Materials with extremely low content of radioactive impurities are required for the construction of successful rare-event detectors, where constraints on naturally occurring radionuclides such as 232Th and 238U typically fall in the microBq/kg range or lower, corresponding to parts-per-trillion (ppt) or parts-per-quadrillion (ppq) concentrations. These levels are several orders of magnitude lower than levels found in soil, rocks, and most commercially available materials. Additive-free, ultra-pure electroformed copper, originally developed at PNNL, has been a key material for several neutrinoless double beta decay and dark matter experiments, with 232Th and 238U impurities measured below a fraction of a microBq/kg, in the ppq range. However, its relatively low strength (~33 MPa) means that copper components must be made unusually thick to meet structural requirements. At growth rates on the order of 1 mm/month, producing large-scale, thick electroformed structures becomes both costly and extremely time-consuming. Developing structural materials that retain ultra-low radioactivity while offering significantly higher strength would have a great impact on next-generation low-background experiments.
Previous work has demonstrated that alloying individually electroplated layers of copper and chromium can yield a Cu-Cr alloy with substantially increased yield strength (by ≈50 % relative to pure copper) and acceptable levels of radiopurity, with only ~1% Cr added to the copper matrix. This has driven interest in Cu–Cr alloys with 0.6–1.2 wt% Cr in bulk copper as candidates for low background structural components, potentially enabling reduced copper mass without sacrificing mechanical performance or radiopurity. Here, we investigate the manufacturing of a Cu-Cr alloy by co-electrodeposition, which overcomes drawbacks associated with stacking and subsequently alloying individually plated layers. Furthermore, we replace highly toxic and carcinogenic hexavalent chromium with trivalent chromium.
We present preliminary results from co-deposition of Cu and Cr from low-additive aqueous chloride baths with future radiopurity requirements in mind. Given the complexity of Cr(III) in aqueous solution and its electronegative reduction potential beyond that of water, we also investigate non aqueous baths based on deep eutectic solvent (DES) solutions as an alternative co deposition medium. Early experiments in DES indicate that Cu and Cr can be co deposited, and we are optimizing bath composition and process parameters to approach the desired Cr content while maintaining coherent, structurally robust deposits. We outline our initial electrochemical and microstructural characterization of these deposits, and discuss planned next steps toward alloying and hardening heat treatments, as well as radiopurity assessment for application in low background detector structures.

Speaker: Dr Matthew Newton (Pacific Northwest National Laboratory)

80 Ultra pure copper electroforming at Boulby deep underground laboratory

High purity copper is an attractive material choice for low background detector construction, due to its commercial availability and lack of long-lived radioisotopes. Despite this, copper can still represent an important background, with impurities from the ore, implanted during manufacture or from cosmogenic activation. Underground additive-free electroforming provides a method to produce ultra-pure copper parts with orders of magnitude reduction in background. This contribution will describe a copper electrodeposition facility constructed at Boulby, the UK’s deep underground laboratory, and show results of electroformed copper which is critical for several future experiments. One such experiment DarkSPHERE, a large diameter spherical proportional counter, will be presented along with the near-term plan to electroform a 30cm spherical proportional counter as the first step towards its construction.

Speaker: Giovanni Rogers (University of Birmingham (UK), STFC - Boulby Underground Laboratory)

Bolometers

81 The CROSS Demonstrator: Structure, Low-Background Techniques, and Physics Reach

Cryogenic calorimeters are among the most sensitive detectors for the search for neutrinoless double beta decay ($0\nu\beta\beta$), a hypothetical process whose observation would demonstrate lepton number violation and establish the Majorana nature of neutrinos. The discovery potential of these experiments strongly depends on the suppression of radioactive background especially in the region of interest around the decay $Q$-value.

The CROSS demonstrator, installed at the Canfranc Underground Laboratory in Spain and taking data since October 2025, combines high-resolution cryogenic calorimeters with active particle-identification techniques designed to mitigate the dominant background sources affecting bolometric experiments.

The detector array is based on lithium molybdate (Li$_2$MoO$_4$) and tellurium dioxide (TeO$_2$) crystals operated as bolometers at millikelvin temperatures. Most of the Li$_2$MoO$_4$ crystals (32 out of 36) are enriched in $^{100}$Mo, while all TeO$_2$ crystals are enriched in $^{130}$Te. A major experimental challenge is the rejection of degraded surface $\alpha$ events, which can mimic a potential $0\nu\beta\beta$ signal.

To address this issue, CROSS employs scintillating bolometers coupled to cryogenic light detectors. The simultaneous measurement of heat and scintillation light enables efficient particle identification, since $\alpha$ particles produce significantly less scintillation light than $\beta/\gamma$ interactions at the same energy. The experiment integrates both Germanium and Silicon light detectors, with Silicon-based devices representing a promising and cost-effective solution for future large-scale experiments such as CUPID.

CROSS also incorporates Neganov-Trofimov-Luke (NTL) amplified light detectors. By applying an electric field across the absorber, the thermal signal generated by absorbed scintillation photons is amplified through charge-carrier drift, significantly improving the signal-to-noise ratio. This enhancement is particularly important for pile-up rejection and particle identification at low energy levels.

The demonstrator features a compact geometry, a reduced amount of passive material near the crystals, and stringent radiopurity requirements for detector components, all essential for achieving the ultra-low-background conditions required in rare-event searches.

The CROSS demonstrator represents an important technological step toward the future CUPID experiment, providing a large-scale validation of the detector concepts and background-rejection techniques required for tonne-scale cryogenic experiments.
By combining excellent energy resolution with active particle identification and amplified cryogenic light detection, CROSS aims to significantly improve the background suppression capabilities of bolometric detectors. This is pivotal for next-generation neutrinoless double beta decay experiments such as CUPID, which aim to achieve an ultra-low background index of the order of $10^{-4}$ counts/(keV kg yr), enabling a nearly background-free exploration of the inverted neutrino mass hierarchy region.

Speaker: Roberto Serino (IJCLab - CNRS - Université Paris Saclay)

LRT_abstract.pdf

82 BINGO: toward a background-free ton-scale bolometric search for Neutrinoless Double Beta Decay

BINGO is a technology demonstrator dedicated to the development and validation of novel background suppression techniques for cryogenic calorimetric searches for neutrinoless double beta decay ($0\nu\beta\beta$). The experiment targets a background index at the level of $10^{-5}$ counts/(keV$\cdot$kg$\cdot$yr), paving the way toward a nearly background-free tonne-scale search using the isotopes $^{100}$Mo and $^{130}$Te.
The BINGO design combines several innovative approaches to drastically reduce background contributions. First, a new detector architecture minimizes the exposed surface area of passive materials in the detector array by more than an order of magnitude compared to previous-generation experiments. Second, the detector core is surrounded by a compact array of BGO scintillating crystals operated as an active cryogenic veto system to reject external backgrounds. Third, enhanced Neganov–Trofimov–Luke (NTL) light detectors are being developed to suppress pile-up background in $^{100}$Mo-based detectors and to provide efficient $\alpha/\beta$ discrimination for TeO$_2$ bolometers.
A dedicated cryogenic infrastructure has been installed and commissioned at the Modane Underground Laboratory (LSM), providing a low-background environment for detector integration and operation. Prototype detector arrays are currently under study to validate the proposed technologies and optimize the final experimental configuration. A first physics campaign with the MINI-BINGO setup is foreseen in fall 2026.
We present the overall detector concept, the status of the cryogenic infrastructure and detector R&D, results obtained with prototype technologies in proof-of-concept measurements, and first preliminary data from underground operations at LSM. In addition, Geant4-based simulations are used to evaluate the expected performance gains and the projected impact of these developments for next-generation CUPID-scale neutrinoless double beta decay experiments.

Speaker: Mrs Claudia Nones (CEA/IRFU/DPhP)

12:40 Lunch

Low-Background Assay Techniques 2

Convener: Grzegorz Zuzel (Jagiellonian University)

83 Rapid low-background radioassay techniques for 210Pb and 3H in materials for rare-event searches

The development of next-generation rare-event experiments requires increasingly sensitive and rapid radioassay techniques for the screening and monitoring of detector materials. In particular, long-lived low-energy emitters such as
$^{210}$Pb and $^{3}$H represent a critical background source for several low-background applications, while remaining challenging to measure with conventional techniques.

In this contribution, we present recent developments in low-background Liquid Scintillation Counting (LSC) techniques performed at the University of Milano-Bicocca using a Wallac Quantulus 1220 system. The main focus is a rapid assay method for $^{210}$Pb in archaeological lead, developed within the R$\&$D activities of the RES-NOVA experiment. By combining optimized chemical preparation, pulse shape analysis (PSA), and low-background counting, the technique enables the simultaneous observation of the $^{210}$Pb decay chain ($^{210}$Pb, $^{210}$Bi, and $^{210}$Po) with sensitivities reaching the sub-Bq/kg level on timescales compatible with material screening and purification monitoring. The effects of chemical and color quenching, detector linearity, ROI optimization, and $\alpha/\beta$ discrimination will be discussed.

Additionally, preliminary investigations on the extension of similar LSC methodologies to $^3$H measurements in PbWO$_4$ crystals exposed to a fast-neutron spectrum at the ISIS ChipIR facility will be presented.
These measurements are relevant for the characterization of neutron-induced and intrinsic backgrounds in cryogenic detectors based on archaeological lead compounds.

These results demonstrate the potential of compact low-background LSC systems as flexible and relatively accessible tools for fast radioassay applications in rare-event physics experiments.

Speaker: Marco Consonni (Università di Milano Bicocca, Istituto Nazionale di Fisica Nucleare)

Rapid_low-background_assay_LRT26_consonni.pdf

84 Decay energy spectroscopy with solid phase extraction for radio-assay of high-purity copper.

Rare event search experiments such as AMoRE require precise radioassay of materials to constrain experiment backgrounds. ICP-MS is sensitive only to long-lived nuclides, while HPGe gamma-ray counting is generally limited by low detection efficiency that scales poorly with sample size. To bypass the limitations of these long-established techniques, we are developing a decay energy spectroscopy technique that uses magnetic microcalorimeters for direct, high-efficiency assay of Ra-226 and Th-228 at the µBq/kg level.

In this method, radium or thorium is chemically extracted from bulk samples into a solution. The solution is deposited and dried on a 1.5 cm × 1.5 cm × 25 µm gold foil. The foil is subsequently folded to enclose the sample, forming a 4π calorimetric absorber. Radioactive decays occurring inside the gold absorber deposit their full decay energy, including that of the alpha particle and recoil nucleus, and are detected as temperature pulses by the magnetic microcalorimeter. Nuclide identification is performed by selecting alpha-decay energies and time-coincidences in accordance with decays in the Ra-226 and Th-228 chains. Energy calibration is established with a Gd-148 alpha source.

We will present the development and validation of this technique with an emphasis on Th-228 assay in NOSV copper samples. Thorium is extracted using UTEVA resin and measured with the MMC-based decay energy spectrometer, with potential to scale to the sub-μBq/kg level. In addition, the sample-deposition efficiency is evaluated using Th-229. These results demonstrate that chemical extraction combined with MMC-based decay energy spectroscopy is a promising technique for improving sensitivities in ultra-low radioactivity assays for rare-event search experiments.

Speaker: jongseok Chung (ChungAng University)

85 Gator: A low-background Germanium facility for high sensitivity gamma-ray spectroscopy

Germanium spectroscopy is a non-destructive screening method that provides precise information on primordial, cosmogenic, and anthropogenic radioactive contaminants using high-resolution $\gamma$-ray spectroscopy. Gator is a high-sensitivity, low-background germanium spectrometer that is installed at the Gran Sasso Underground Laboratory (LNGS) in Italy. It is operated at an average depth of 3600 meter water equivalent and is used for material screening and selection in ultra-low-background, rare-event search experiments in astroparticle physics, such as XENONnT, LEGEND and DARWIN/XLZD, and also used to characterize the radioactivity level in samples from the Bedretto Lab, a proposed underground laboratory in Switzerland with a comparable cosmic muon shielding to LNGS. In addition to being a screening facility, the instrument has also been used to perform high-precision searches for possible violations of the Pauli Exclusion Principle. The 2.2 kg p-type HPGe crystal housed in an electro-refined copper cryostat is equipped with a passive shield made of layers of copper, lead and polyethylene. The sample cavity is purged with gaseous nitrogen maintained at positive pressure for radon suppression. The background rate is (82.0 $\pm$ 0.7) counts/(kg $\cdot$ day) in the energy range 100-2700 keV. The data acquisition system and the electronics were upgraded recently which reduced the low energy electronic noise below 100 keV. This work demonstrates the stability of key operational parameters under operating conditions. The sample analysis procedure is summarized and the sensitivity of Gator is demonstrated by examining one material sample from the Bedretto laboratory site.

Speaker: Aravind Remesan Sreekala (University of Zurich)

86 Development of an Ultrasensitive ICP-MS Assay Method for the Determination of Long-lived Radioisotopes in Gadolinium Used in Scintillator Materials

The development of ultra-low background gadolinium-loaded liquid scintillator (Gd-LS) is critical for current and next-generation experiments in neutrino and rare-event physics, including supernova neutrino detection, reactor monitoring, and as a neutron veto in dark matter searches. The presence of trace radioactive contaminants can introduce backgrounds that severely limit sensitivity. In this work, we present a novel, highly sensitive inductively coupled plasma mass spectrometry (ICP-MS) assay method capable of quantifying ²³⁸U, ²³⁵U, ²³²Th, and ⁴⁰K at microBq/kg levels in organic gadolinium compounds used in scintillator production. The developed method incorporates an ultra-clean dry ashing and separation procedure that minimizes contaminant introduction during sample processing as well as spectral interferences and matrix effects during mass spectrometric analysis. The method has been successfully applied to the organic-based Gd(TMHA)₃ material used in the LUX-ZEPLIN (LZ) experiment’s Gd-LS neutron veto, enabling a better understanding of the background contributions and ultimate sensitivity reach of the detector. This method provides a foundation for quality assurance in future low-background experiments utilizing Gd-LS and offers a high-throughput approach capable of processing batches of scintillator precursor compounds within days at sensitivities not achievable using other techniques.

Speaker: Isaac Arnquist (Pacific Northwest National Laboratory)

15:15 Coffee

Quantum Technologies

Convener: Ashlea Kemp (STFC)

87 Background concerns in superconducting qubits and other quantum technologies

Speaker: Ben Loer (Pacific Northwestern National Laboratory)

88 Superconducting Qubits as Particle Detectors

The discovery that superconducting qubits are sensitive to ionizing radiation has sparked interest beyond the quantum research community. Recent experiments, capable of detecting single interactions from cosmic muons and γ-rays, have highlighted the potential of these devices as a novel type of particle detector. As research in this field is still at an early stage and many questions remain unanswered, precious insights can come from the study of correlated errors, i.e. simultaneous state decays of multiple qubits on the same chip.
In this contribution we will present the new results achieved at the Gran Sasso National Laboratory (LNGS), Italy, where we measured correlated errors in two transmon qubits produced by a Ra-224 source. A Neutron Transmutation Doped (NTD) thermistor was glued on the same chip of the two qubits, allowing for the reconstruction of the spectrum of the deposited energy and the estimation of the detection efficiency of the two qubits. On the same chip was glued also a heater, i.e. a resistor, to study the response of the qubits to thermal phonons. A novel analysis strategy allowed us to identify radiation-induced events with a detection efficiency much higher than what obtained in previous studies, marking further progress towards the realization of a qubit-based particle detector.

Speaker: Francesco De Dominicis (Istituto Nazionale di Fisica Nucleare)

LRT2026_DeDominicis.pdf

89 Radiopurity material assays and radiation exposure projections for superconducting qubit measurements at SNOLAB

Interactions of cosmic rays and ionization radiation pose a significant challenge to the development and operation of state-of-the-art quantum devices such as superconducting quantum circuits. Shielded by 2km of rock overburden, the Cryogenic Underground TEst facility (CUTE) at SNOLAB provides a unique ultra-low radiation environment to probe the performance of quantum technologies with a particular interest in quantum coherence time studies. We present the findings of an extensive material assaying program in preparation for the first underground operation of superconducting qubits at SNOLAB. Monte-Carlo (Geant4) estimations of expected rates, energy spectra, and dominant interaction types of radioactive background sources and contaminants are presented for a proposed quantum device payload to be operated in CUTE. Finally, we outline how crystal dynamics simulations using the G4CMP solid state physics extension for Geant4 can inform the community-wide efforts to identify effective mitigation strategies following high-energy particle impacts.

Speaker: Stefan Zatschler (Laurentian University, University of Toronto, SNOLAB)

LRT2026_Qutebits_SNOLAB_szatschler.pdf

Closing Remarks

90 Closing Remarks

Speaker: Paul Scovell (STFC)