CSI(TL)-PHOTODIODE DETECTORS FOR SPECTROSCOPY AT LOW RADIATION-LEVELS

Some aspects of CsI(Tl)-photodiode detectors relevant for applications in low level radiation spectroscopy in the MeV energy range have been studied with a view to a sensitive search for the lepton number viola ting neutrinoless double beta decay of Mo-100. Energy resolutions of s lightly less than 100 keV (FWHM), limited by electronic noise, have be en obtained for crystal masses up to more than 3 kg. The improved ener gy resolution facilitates a very sensitive investigation of crystal co ntaminations with nuclides of the Th and U chains by spectroscopic ana lysis of alpha-decays. The cleanest crystal was free of U and Th conta minations at the detection limit of 0.27 alpha-decays per kg and h, a radiopurity well sufficient for applications in low level spectroscopy .