Beta Decay Experiments

Abstract

One of the main problems to be studied with cryogenic detectors is the search for a finite value of the neutrino mass. In fact recent experiments on neutrino oscillations have shown that the mass difference between neutrinos of different flavours is different from zero. This stimulates searches on the absolute value of the neutrino mass, which can be very effectively performed with cryogenic detectors. One option is the precise determination of the spectrum of single beta decays, which has been so far mainly obtained by measuring the energy spectrum of decay electrons. Experiments carried out with the bolometric technique are complementary, since they allow measuring the total energy released by the decay into the detector, including for instance the energy spent into excitation of atomic or molecular excited levels. The spectra of beta decays with low transition energy allows also to investigate the crystal structure with Beta Environmental Fine Structure (BEFS). Cryogenic detectors are very promising to study processes like electron capture also in view of experiments on solar neutrinos. Another way to investigate the absolute value of neutrino mass is neutrinoless double beta decay, whose existence would imply not only lepton number violation, but also a non vanishing mass for the neutrino. While searches on single beta decays are carried out with microcalorimeters, double beta decay experiments require large mass detectors, installed underground in order to avoid the cosmic ray background. Unlike conventional techniques they allow a wide choice of nuclear candidates for double beta decay. The use of cryogenic detectors in searches on weak interactions are by no means limited to these two subjects. Many rare decays can be investigated in order to obtain important results in low energy nuclear physics and in other fields like geochronology or even material science.