A compact Germanium spectrometer for nuclear astrophysics

Emission from electron-positron annihilation at 511 keV was the first extrasolar gamma-ray line ever detected. Despite more than 30 years of theoretical and observational progress, the origin of the positron population has yet to be identified, with potential candidates ranging from microquasars and X-ray binaries to annihilation or decay of dark matter particles. At energies between 200 keV and several MeV, where positron annihilation and most other gamma-ray lines of interest are located, the largest source of instrumental background are secondary protons, neutrons, and photons produced by the spacecraft when it is irradiated by cosmic rays in a space environment. This background is the main factor limiting the sensitivity of current gamma-ray spectrometers, and is proportional to the amount of mass around the detectors. We present progress towards a compact, modular, high-purity Germanium spectrometer that can be integrated into future astrophysics payloads and be the basis of small-satellite missions. A CubeSAT or SmallSAT-class mission based on compact spectrometer modules could have up to 30% of the total spacecraft mass in active germanium crystal, compared to 0.6% in current missions like INTEGRAL, leading to more than an order-of-magnitude improvement in signal-to-noise ratio due the reduction in overall spacecraft mass.