Gamma Ray Detection Efficiency of GAGG Crystal Scintillator Using Three Tagged Gamma Ray Techniques

A CubeSat with a prototype scintillating detector with a sensitive volume of GAGG crystal is being developed with a possible launch date of 2025. Its purpose is to characterize the background signals that mimic the neutrino interaction that the nuSOL team is looking for. An important part of the characterization of the backgrounds and the expected real signal is understanding the gamma ray detection efficiency of the prototype detector. To this end we have used and developed three techniques to do an absolute measurement of gamma ray efficiency. The first is using EC sources that emit an X-ray before prompt emission of a de-excitation gamma ray, specifically Zn-65 and Mn-54. The second is using a beta + decay source wherein a positron annihilates on an atomic shell electron producing two back-to-back 511 keV gammas followed promptly by a de-excitation gamma, specifically Na-22. The third is using a gamma cascade of two near-simultaneous de-excitation gammas from the same nucleus, specifically from Co-60 decay.