The solar neutrino capture rate measured by SAGE is well below that pr
edicted by solar models. To check the overall experimental efficiency,
we exposed 13 tonnes of Ga metal to a reactor-produced 517 kCi source
of Cr-51. The ratio of the measured production rate to that predicted
from the source activity is 0.95 +/- 0.11(stat) +0.05/-0.08(syst). Th
is agreement verifies that the experimental efficiency is measured cor
rectly, establishes that there are no unknown systematic errors at the
10% level, and provides considerable evidence for the reliability of
the solar neutrino measurement.