We are planning to launch a 50kg-class satellite named INSPIRE, equipped with a small, high-performance Hybrid Compton Camera (HCC) for MeV gamma-ray astronomy.Since the launch of the COMPTEL satellite in 1991, there have been limited observations in the MeV gamma-ray band. However, this energy range is crucial for studying nucleosynthesis processes. INSPIRE aims to conduct a wide-area survey of nuclear gamma rays from the galactic plane and includes gamma-ray observations of solar flares as one of its objectives. Equipped with a hybrid Compton camera (HCC) system, INSPIRE can perform simultaneous X-ray and gamma-ray imaging. This is achieved by integrating the features of both Compton and pinhole cameras within a single detector system. The system includes two sensor layers of large-area Silicon Photomultiplier (SiPM) arrays, optically coupled with GAGG scintillators. This configuration enables simultaneous imaging of gamma rays from 30 to 200 keV in pinhole mode and from 200 to 3000 keV in Compton mode. Its intrinsic efficiency and angular resolution are comparable to those of COMPTEL.The INSPIRE satellite is being developed as the successor to PETREL, which is currently being prepared for launch, with a planned launch in 2027.
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.
The MeV band covers the physics of the lowest energy end of the non-thermal universe and nuclear reactions in metal synthesis and/or matters interacting with cosmic rays. Nevertheless, sensitivity in this band is still limited. Improving MeV sensitivity is one of the most important issues in modern astronomy. The soft gamma-ray detector (SGD) onboard the Hitomi satellite launched in 2016 was an innovative narrow field-of-view semiconductor Compton telescope (SCT), which aims at background reduction through deep active-shielding combined with SCT using Si and CdTe, a Si/CdTe-SCT. Although with a limited operation time, it is the sole SCT proven in orbit to date, and succeeded in detecting ∼ 100 keV polarization with only 5 ks exposure. Based on these achievements, we propose a new approach “narrow field-of-view Si/CdTe-SCT at balloon altitude”. At the altitude of 32-40 km, detectors do not suffer severe proton bomberment, which was one of the major contributor to the SGD background, while able to observe MeV gamma rays from the universe. Atmospheric gamma rays is non-negligible, but as it is stronger near horizon, narrowing the field-of-view and aiming around zenith will cut most of them. The detector loses wide field of view, but can be used as a probe in sub-MeV band. As the first step of this approach, we are planning a balloon experiment, miniSGD, to confirm the concept. It is very compact and not aiming at real observation, but has all the components integrated within the 40 × 40 × 50 cm3 volume, including detectors, electronics and the collimator. The Si/CdTe-SCT was made of a single layer of 0.5 mm thick double-sided Si strip detectors (DSSDs) and newly developed 2 mm thick CdTe double sided strip detectors (CdTe-DSDs), surrounded by nine units of 2-3 cm thick BGO scintillator crystals. The miniSGD experiment is to fly as a piggy-back payload in the 2023 Spring campaign of JAXA Ballooning team at Alice Springs, Australia. Technologies to be verified in miniSGD are also applicable to the future hard X-ray missions, such as the FORCE mission.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.