The Soft Gamma-ray Detector on Hitomi
This photo shows one of the two Soft Gamma-ray Detector (SGD) units mounted on the outer panels of the Hitomi satellite.
The instrument consists of a pair of identical non-focussing Compton-cameras, sensitive to photons with energy between 40 keV and 600 keV. Each camera consists of a stack of Si and CdTe pixellated detectors. The narrow field-of-view collimator outperforms the background rejection capability of previous soft-gamma ray detectors.
Events are recorded when photons interact twice with the detector, first by Compton scattering in the stack of Si strip detectors, and then by photo-absorption in the CdTe part (Compton mode). By measuring the location and energy of the two interactions, it is possible to estimate the energy and incoming direction of the incident gamma ray.
While primarily a spectrometer in the 40–600 keV energy band, the SGD is also sensitive to polarisation in the 50–200 keV energy band.
Hitomi (known as ASTRO-H prior to launch) is a high-energy astrophysics space observatory, developed by the Japan Aerospace Exploration Agency (JAXA) in collaboration with institutions in Japan, the US, Canada, and Europe.