Prototype thermal detectors for a 187Re neutrino mass experiment

We report on a new method to measure the electron antineutrino mass, consisting of the end-point study of Re-187 beta-spectrum (Q-value=2.6 keV) collected calorimetrically (source=detector approach) with high energy resolution and statistics. The proposed detector is a micro-bolometer, single or in an array structure, containing a total rhenium mass of similar to 1 mg, operated at a temperature of a few tens of mK and able to reach 10 eV energy resolution. As phonon sensors, we are developing silicon thermistors doped by implantation; some tests are performed also with neutron transmutation doped germanium thermistors. We have obtained up to now promising energy resolutions down to similar to 11 eV with tin absorbers (as test devices) and similar to 70 eV with rhenium absorbers.