A BROMINE CRYOGENIC DETECTOR FOR SOLAR AND NON SOLAR-NEUTRINO SPECTROSCOPY

We suggest ''on line'' detection of solar and non solar neutrinos by interactions on Br-81 leading to the excited state at 190.4 keV of Kr-81. The signal for a monocromatic neutrino will consist of a delayed coincidence between an electron pulse corresponding to the neutrino energy decreased by 471 keV, and the 190.4 keV de-excitation pulse. The coincidence time (13.1 s in average) allows an efficient use of large thermal detectors operating at low temperature which have been proved to provide energy resolutions and stability comparable to those of Ge diodes. We have operated with reasonable results for the first time crystals of NaBr as thermal detectors. At present their mass and thermal properties do not fulfil however the requirements posed by a full scale neutrino experiment and improved procedures have to be studied for their preparation. The alternative approach of an array of CsBr scintillators is also considered. The thermal method suggested here could in principle enable a very strong background rejection with respect to other techniques adopted or to be adopted in solar neutrino experiments. Construction of a very large (100 tons) array looks however a formidable task both from the technical and from the financial point of view. Lower mass detectors to search for interactions of ''artificial'' neutrinos or of dark matter particles are being considered as an intermediate and more realistic approach.