SAGE was devised to measure the radio-chemical solar neutrino flux based on the inverse beta decay reaction, 71Ga
The target for the reaction was 50-57 tonnes of liquid gallium metal stored deep (2100 meters) 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 (
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 continued to run in August 2011 with only a few brief interruptions in the timespan.
The extractions for the Cr experiment took place between January and May 1995 and the counting of the samples lasted until fall.
This indicates that the discrepancy between the solar model predictions and the SAGE flux measurement cannot be an experimental artifact.
In 2003-2004, a 37Ar neutrino source was made by irradiation of calcium oxide in the BN-600 reactor followed by chemical separation of argon.
Following the report of the anomaly in 2006, physicists began to explore potential explanations for the observed deficit.
[9][10] This strengthened the evidence for the anomaly and pushed the focus towards investigating potential new physics beyond the standard three-neutrino model.
A 2013 review combined the gallium results with data from reactor antineutrino experiments, arguing for a consistent pattern of electron (anti)neutrino disappearance at short baselines and highlighting the need for more precise measurements and dedicated experiments to definitively confirm or refute the sterile neutrino interpretation.
[16] In June 2022, the BEST experiment released two papers observing a 20-24% deficit in the production the isotope germanium expected from the reaction
, confirming previous results from SAGE and GALLEX on the so called "gallium anomaly" pointing out that a sterile neutrino explanation can be consistent with the data.
[17][18][19] Further work have refined the precision for the cross section of the neutrino capture in 2023[20] which was proposed as a possible inaccuracy source back in 1998[21] as well as half-life of