SAGE (Soviet–American Gallium Experiment)

SAGE (Soviet–American Gallium Experiment, or sometimes Russian-American Gallium Experiment) is a collaborative experiment devised by several prominent physicists to measure the solar neutrino flux.

The Experiment

SAGE was devised to measure the radio-chemical solar neutrino flux based on the inverse beta decay reaction, ⁷¹Ga( ν_e,e^-} )⁷¹Ge. The target for the reaction was 50-57 tonnes of liquid gallium metal stored deep underground at the Baksan Neutrino Observatory in the Caucasus mountains in Russia. About once a month, the neutrino induced Ge is extracted from the Ga. ⁷¹Ge is unstable with respect to electron capture (t1 / 2 = 11.43 days) and, therefore, the amount of extracted germanium can be determined from its activity as measured in small proportional counters.

The experiment had begun to measure the solar neutrino capture rate with a target of gallium metal in December 1989 and is running up to now (as of January 2010) with only a few brief interruptions. The experiment has measured the solar neutrino flux in 168 extractions between January 1990 and December 2007. The current result of the experiment based on the whole 1990-2007 set of data is 65.4 +3.1/-3.0 (statistical) +2.6/-2.8 (systematic) SNU. This represents only 56%-60% of the capture rate predicted by different Standard Solar Models, which predict 138 SNU.

The collaboration has used a 518 kCi ⁵¹Cr neutrino source to test the experimental operation. The energy of these neutrinos is similar to the solar 7Be neutrinos and thus makes an ideal check on the experimental procedure. The extractions for the Cr experiment took place between January and May 1995 and the counting of the samples lasted until fall. The result, expressed in terms of a ratio of the measured production rate to the expected production rate, is 1.0±0.15. This indicates that the discrepancy between the solar model predictions and the SAGE flux measurement cannot be an experimental artifact. Also calibrations with a ³⁷Ar neutrino source had been performed.

Members of SAGE

SAGE is led by the following physicists:

Vladimir Gavrin
Georgiy Zatsepin (Joint Institute for Nuclear Research, Russia)
Tom Bowles (Los Alamos)

See also

GALLEX/GNO was the second (of two) large gallium-germanium radiochemical experiment. It was running in 1991-2003.
Hans Bethe was the architect of the theory of nuclear fusion reactions in stars.
The University of Washington is playing a major role in the statistical analysis of the SAGE data and in the determination of systematic uncertainties. They are very active in the remaining analysis of the Cr experiment data as well as the solar neutrino data.

Literature

SAGE Collaboration. Measurement of the solar neutrino capture rate with gallium metal. III: Results for the 2002--2007 data-taking period. Phys.Rev. C80:015807, 2009. See also arXiv:0901.2200