Study of a high intensity 746 keV neutrino source for the calibration of solar neutrino detectors

Abstract We describe the test production of a 0.94 PBq (25 400 Ci) source of 746 keV neutrinos coming from the electron capture decay of 51 Cr. This is the first time that such a source has been produced. It was obtained by neutron activation of 12.5 kg of natural granular chromium at the Siloe reactor at Grenoble. If this nuclear reactor were devoted exclusively to the production of 51 Cr from natural chromium, we calculate that the highest activity that could be produced would be around 29 PBq (0.8 MCi) in 45 days of irradiation, for 125 kg of target. With chromium enriched in 50 Cr, we could get around 40 PBq (1.08 MCi) in an irradiation of 21 days, for 45 kg of target containing 17% 50 Cr. Such sources are planned for use in calibrating forthcoming solar neutrino detectors, especially the gallium detector to be installed in the Gran Sasso Underground Laboratory. To obtain a precision of 10% in such calibrations would require either three sources made from natural chromium (i.e. three reactor irradiations of 45 days each) or two sources made from enriched chromium (two irradiations of 21 days each).