CRYOGENIC DETECTION OF BE-7 WITH BERYLLIUM METAL ABSORBER FOR LITHIUMSOLAR-NEUTRINO EXPERIMENT

A cryogenic micro-calorimeter to detect the Be-7 electron capture deca y has been developed. The detector absorber is a beryllium metal foil which has been previously irradiated by protons in order to produce th e Be-7 isotope. The 112 eV spectral line corresponding to the Be-7 K-c apture decay to the Li-7 ground stare (Auger-electron plus the nuclear recoil energy) has been successfully detected with an energy resoluti on of 53 eV FWHM. The observed decrease in the rate of the absorber ac tivity corresponds to the expected Be-7 half-life. The obtained result s show that the 112 eV Be-7 spectral line can be detected by a cryogen ic mu-calorimeter with an efficiency close to 100%. This cryogenic met hod solves the principal problem in the development of a lithium radio chemical solar neutrino detector.