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

We suggest ''on line'' detection of solar and non solar neutrinos by i nteractions on Br-81 leading to the excited state at 190.4 keV of Kr-8 1. The signal for a monocromatic neutrino will consist of a delayed co incidence between an electron pulse corresponding to the neutrino ener gy decreased by 471 keV, and the 190.4 keV de-excitation pulse. The co incidence time (13.1 s in average) allows an efficient use of large th ermal detectors operating at low temperature which have been proved to provide energy resolutions and stability comparable to those of Ge di odes. We have operated with reasonable results for the first time crys tals of NaBr as thermal detectors. At present their mass and thermal p roperties do not fulfil however the requirements posed by a full scale neutrino experiment and improved procedures have to be studied for th eir preparation. The alternative approach of an array of CsBr scintill ators is also considered. The thermal method suggested here could in p rinciple enable a very strong background rejection with respect to oth er techniques adopted or to be adopted in solar neutrino experiments. Construction of a very large (100 tons) array looks however a formidab le task both from the technical and from the financial point of view. Lower mass detectors to search for interactions of ''artificial'' neut rinos or of dark matter particles are being considered as an intermedi ate and more realistic approach.