Final results of the 51Cr neutrino source experiments in GALLEX

Abstract The radiochemical GALLEX experiment, which has been measuring the solar neutrino flux since May 1991, has performed an investigation with two intense 51 Crneutrino sources (> 60 PBq) that were produced in the Siloe nuclear reactor and used at the Gran Sasso National Laboratory, one between June and October 1994, and the second between October 95 and February 96. The ratio, R, of the the neutrino source strength derived from the measured rate of 71 Geproduction, divided by the directly determined source strength is R=1.01  +0.12 −0.11 for the first source and R=0.84  +0.12 −0.11 for the second one. The combined value of R for the two source experiments is R=0.93 ± 0.08. It shows that the > 40 % deficit of solar neutrino flux observed by GALLEX cannot be attributed to experimental artifacts and demonstrates the absence of any significant unexpected systematic errors at the 10 % level.