Speaker
Description
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.