Speaker
Description
The India-based tin detector (TIN.TIN) proposes to explore neutrinoless double beta decay in the isotope $^{124}Sn$ by employing an array of cryogenic tin-based bolometers which will be operated at ~10 mK. However, pure tin is susceptible to tin pest, an allotropic phase transition of tin near ambient conditions which results in the mechanical failure of the tin sample. This poses a concern for the longevity of the bolometer array. Sn-Bi alloys are resistant to tin pest and suitable for the fabrication of superconducting bolometers.
The present work reports the evaluation of the anticipated internal background from Sn-Bi bolometers. $^{209}Bi$ can decay by emitting an $\alpha$ particle of ~3.1 MeV. However, the $\alpha$ decay is extremely rare, having a half-life of $ 2 \times 10^{19}y$ (comparable to the typical half-life of a $\beta\beta$ candidate). The background from surface $\alpha$ radiation of $^{209}Bi$ was estimated using GEANT4 simulations. The anticipated internal background from U/Th impurities was also simulated and compared to the background from $^{209}Bi$ $\alpha$ decay. The $\alpha$ decay from $^{214}Bi$ (product of the $^{238}U$ chain) was found to be the limiting background, while the radioactivity of $^{209}Bi$ had negligible effect on the background (~$10^{-5} cts$.$keV^{-1}$.$kg^{-1}$.$y^{-1}$).
