Prototype fine-imaging narrow field of view semiconductor Compton telescope with shielded coded-mask, mini-SGI

Semiconductor Compton telescope (SCT) is one of the promising technologies in cosmic MeV gamma-ray observation, because of good angular resolution measure thanks to its high energy and positional resolutions. However, it cannot be better than a few degrees because of quantum limitation, known as doppler broadening. With improving sensitivity in MeV astronomy, realization of 10-arcmin-level of angular resolution is becoming more important. Combining a coded-aperture mask imaging to SCT is the simplest measure to obtain this level of angular resolution in MeV astronomy. Since the mask made of heavy metal is a BGD source and contribution from bright sources and CXB limits the statistical significance of the mask decoding, we propose the concept of attaching a coded mask to a narrow-field Si/CdTe SCT such as the SGD on the ASTRO-H mission. We developed a concept verification system, mini-SGI, adopting 0.5 mm thick DSSDs and 2 mm thick CdTe-DSD, covered with BGO active shield. By irradiating a ¹³³Ba source, we succeeded to obtain 1° resolution coded-mask imaging applied to Compton reconstructed image with ARM resolution of 9.8 degree and 3.0 degree to 81 keV and 356 keV lines, respectively.