MeV gamma-ray band is the boundary between the thermal and non-thermal particle worlds and are very important for understanding high-energy phenomena in the universe. The SGD onboard the ASTRO-H satellite was a narrow field of view Compton telescope that combines a Si/CdTe semiconductor Compton camera and a deep active shield, and has demonstrated high performance in orbit. We are proposing a balloon experiment based on this concept. As the first step. we are developing a proof-of-concept mission, miniSGD.
miniSGD consists of a semiconductor Compton camera with two 0.5 mm thick Si double-sided strip detectors (DSSD) and four 2 mm thick CdTe double-sided strip detectors (CdTe-DSD), and nine 20-30 mm thick BGO scintillators surrounding them. Although the effective area is small because it is a proof-of-concept mission, it aims to achieve higher positional resolution than SGD, and combines all technical items needed in the full mission.
In this presentation, we will report the current status of the development of miniSGD and its performance evaluation. Because the original balloon flight was planned in April 2023, miniSGD was completed by November 2022. Later this flight was canceled unfortunately, and we are now aiming for the next window. Regardless, performance evaluation and study of optimization are on-going. Specifically, we developed a simple depth-of-interaction determination logic and its calibration scheme for the 2 mm thick CdTe-DSD in miniSGD. By introducing this logic, the ARM angular resolution has improved by a factor of 2. Further analysis technique improvements are underway.