Speaker
Description
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.