A compact gamma-ray spectrometer for nuclear astrophysics and planetary science

The source of galactic electron-positron annihilation 511 keV line has yet to be determined. Candidate sources include compact objects, radionuclides from stellar explosions, or the decay of dark matter particles. A major impediment to sensitive astrophysical gamma-ray spectroscopy is instrumental background. In the 200 keV–2 MeV energy range, cosmic-ray irradiation of spacecraft material results in contamination of secondary protons, neutrons, and gamma rays. This contamination is proportional to the spacecraft mass. A detector which maximizes the active detector mass fraction is the best way towards mapping the 511 keV sky and performing gamma-ray spectroscopy of astrophysical sources. We present progress in designing and building a compact, modular gamma-ray spectrometer that can be integrated into future spacecraft missions or as a small-satellite mission. A CubeSAT or SmallSAT-class mission based on such a design would improve sensitivity by an order-of-magnitude over current instruments like INTEGRAL-SPI by having a mass fraction of over 30% compared to INTEGRAL’s 0.6%.