Penning-trap Q -value determination of the Ga71(ν,e−)Ge71 reaction using threshold charge breeding of on-line produced isotopes

We present a first direct Q -value measurement of the Ga71(ν,e−)Ge71 reaction using the TITAN mass-measurement facility at ISAC/TRIUMF. The measurements were performed in a Penning trap on neon-like 71 Ga 21+ and 71 Ge 22+ using isobar separation of the on-line produced mother and daughter nuclei through threshold charge breeding in an electron-beam ion trap. In addition, isoionic samples of 71 Ga 21+ and 71 Ge 21+ were stored concurrently in the Penning trap and provided a separate Q -value measurement. Both independent measurements result in a combined Q -value of 233.5±1.2 keV, which is in agreement with the previously accepted Q -value for the ν cross-section calculations. Together with a recent measurement of the ν -response from the excited states in 71 Ge, we conclude that there are no further uncertainties in the nuclear structure, which could remove the persistent discrepancy between the SAGE and GALLEX calibration measurements performed with neutrinos from reactor-produced 51 Cr and 37 Ar sources and the theoretical expectation.