  We study the online detection by gallium capture of mono-energetic neutrinos
produced by a $^{51}$Cr radioactive source in a scintillation experiment. We
find that cerium-doped gadolinium aluminum gallium garnet (GAGG) is a suitable
scintillator which contains about 21% of gallium per weight and has a high mass
density and light yield. Combined with a highly efficient light detection
system this allows tagging of the subsequent germanium decay and thus a clean
distinction of gallium capture and elastic neutrino electron scattering events.
With 1.5 tons of scintillator and 10 source runs of 3.4MCi, each, we obtain
about 760 gallium capture events with a purity of 85% and 680,000 neutrino
electron scattering events, where the latter provide a precise normalization
independent of any nuclear physics. This configuration would allow to test the
gallium anomaly at more than $5\sigma$ in an independent way.
