Status of the Soviet-American gallium experiment B y 0. L. A nosov , E. L. F aizov , V. N. G avrin , A. V. K alikhov , T. V. K nodel , 1.1. K nyshenko , V. N. K ornoukhov , I. N. M irmov , A. V. O strinsky , A. M. P shukov , A. A. S hikin , P. V. T imofeyev , E. P. V eretenkin , G. T. Z atsepin Institute forNuclear Research of the Russian Academy of Sciences T. J. B owles , S. R. E lliott 1, J. S. N ico , H. A. O ’B rien , D. L. W ark 2, J. F. W ilkerson Los Alamos National L a b o r a t o r y , Los Alamos, NM 87545, U.S.A. B. T. C leveland , R. D avis , J r , K. L ande University of Pennsylvania, Philadelphia, Pennsylvania 19104, U.S.A. M. L. C herry Louisiana State University, Baton Rouge, Louisiana 70803, U.S.A. AND R. T. K ouzes 3 Princeton University, Princeton, New Jersey 08544, U.S.A. A radiochemical 71Ga-71Ge experiment to determine the primary flux of neutrinos from the Sun began measurements of the solar neutrino flux at the Baksan Neutrino Observatory in 1990. The number of 71Ge atoms extracted from 30 tons of gallium in 1990 and from 57 tons of gallium in 1991 was measured in 12 runs during the period of January 1990 to December 1991. The combined 1990 and 1991 data-sets give a value of 58+17/ —24 (stat) + 14 (syst) SNU. This is to be compared with 132 + 7/ —5 SNU predicted by the Standard Solar Model. 1. Introduction A fundamental problem during the past two decades has been the large deficit of the solar neutrino flux observed in the radiochemical chlorine experiment (Davies et at. 1991) compared with the Standard Solar Model (SSM) theoretical predictions (Bahcall & Ulrich 1988 ; Turcke-Chieze 1988). Recent results of the Kamiokande II water Cherenkov experiment (Hirata et at. 1990) have confirmed this deficit. These results may be explained by deficiencies in the solar model in predicting the 8B neutrino flux or may indicate the possible existence of new properties of the neutrino (Bahcall 1989). A radiochemical gallium experiment can help determine the role new neutrino properties may play in the suppression of the solar neutrino flux. An experiment using 71Ga provides the only currently feasible means to measure low energy solar neutrinos produced in the proton-proton (p-p) reaction (Kuzmin 1966). 1 Present address: L-421, Lawrence Livermore National Laboratory, Livermore, CA 94550, U.S.A. 2 Present address: Department of Nuclear Physics, Oxford University, Keble Road, Oxford OX1 3RH, U.K. 3 Present address: Batelle Pacific Northwest Laboratories, P.O. Box 999, Richland, WA 99352, U.S.A. Phil. Trans. R. Soc. Lond. A (1994) 346, 15-21 Printed in Great Britain 15 © 1994 The Royal Society Downloaded from https://royalsocietypublishing.org/ on 20 February 2022