The cadmium zinc TElluride Radiation Imager, or TERI, is an instrument to space-qualify large-volume 4×4×1.5 cm3 pixelated CdZnTe (CZT) detector technology. The CZT’s anode is composed of a 22×22 array of pixels, whereas the cathode is planar. TERI contains four of those crystals with each pixel having an energy range of 40 keV up to 3 MeV with a resolution of 1.3% full-width-at-half maximum at 662 keV all while operating in room temperature. As the detectors are 3D position sensitive, TERI can Compton image events. TERI is fitted with a coded-aperture mask, which permits imaging of low-energy photons in the photoelectric regime. TERI’s primary mission is to space-qualify large-volume CZT and measure its degradation due to radiation damage in a space environment. Its secondary mission includes detecting and localizing astrophysical gamma-ray transients. TERI is manifested in the Department of Defense’s STP-H10 mission for launch to the International Space Station in early 2025.
The ComPair gamma-ray telescope is a technology demonstrator for a future gamma-ray telescope called the All-sky Medium Energy Gamma-ray Observatory (AMEGO). The instrument is composed of four subsystems, a double-sided silicon strip detector, a virtual Frisch grid CdZnTe calorimeter, a CsI:Tl based calorimeter, and an anti-coincidence detector (ACD). The CsI calorimeter's goal is to measure the position and energy deposited from high-energy events. To demonstrate the technological readiness, the calorimeter has flown onboard a NASA scientific balloon as part of the GRAPE-ComPair mission and accumulated around 3 hours of float time at an altitude of 40 km. During the flight, the CsI calorimeter observed background radiation, Regener-Pfotzer Maximum, and several gamma-ray activation lines originating from aluminum.
The GAGG Radiation Instrument (GARI) is designed to space-qualify a compact, high-sensitivity gamma-ray spectrometer for astrophysical and defense applications and has completed over one year of operations on the International Space Station (ISS). The on-orbit activation of the GAGG crystal induced by the radiation background was measured. Characteristic gamma-ray lines present in the on-orbit spectra were compared to ground-based tests for identification. The radiation background, including the particle-induced internal activation of the crystal, affects the sensitivity of the instrument. We also show the degradation in the performance of the silicon photomultiplier (SiPM) readout (known to be sensitive to radiation damage). Results shown here will be useful in predicting the performance of larger instruments that use GAGG scintillator technology for gamma-ray spectroscopy.
The Neutron Radiation Detection Instrument-1A (NeRDI-1A) is a neutron sensor on the International Space Station (ISS) as part of the Department of Defense Space Test Program (STP) mission STP-H9. NeRDI-1A uses the scintillator Tl2LiYCl6:Ce as well as three Domino microstructured semiconductor neutron detectors (MSNDs) with varying levels of moderation and an EJ-270 plastic scintillator. The primary objective of NeRDI-1A is to space qualify TLYC and MSND detectors by studying the effects of on-orbit radiation background on the performance of these detectors over the nominal one-year mission. NeRDI-1A was launched to the ISS on 15 March 2023 GMT aboard SpX-27.
The GAGG Radiation Instruments (GARI), two identical instruments, are designed to space-qualify new gamma-ray detector technology for space-based astrophysical and defense applications. The detector technology offers improved energy resolution, lower power consumption and reduced size compared to similar systems. Each identical GARI instrument consists of a two cerium-doped gadolinium aluminum gallium garnet (GAGG (Gd3(Al,Ga)5O12 :Ce)) scintillation detectors. The crystals have an energy resolution of 4.2% at 662 keV (specified by the manufacturer) compared to the 6.5% of traditional sodium iodide, and the material has found widespread use in medical imaging applications. GAGG is also unique in the fact that it is rugged (resistant to harsh environments) and one of the few non-hygroscopic scintillators available. GARI’s objective is to study the on-orbit internal activation of the GAGG material and measure the performance of the silicon photomultiplier (SiPM) readouts over its 1-year mission. The combined detectors measure the gamma-ray spectrum over the energy range of 0.02 - 8 MeV. The GARI mission payoff is a space-qualified compact, high-sensitivity gamma-ray spectrometer with improved energy resolution relative to previous sensors. Applicable studies in solar physics and astrophysics include solar flares, Gamma Ray Bursts, novae, supernovae, and the synthesis of the elements. Department of Defense (DoD) and security applications are also possible. Construction of the GARI instruments has been completed, and both instruments are being integrated onto their respective platforms. Both instruments are expected to launch in December of 2021 onboard STP-H7 and STP-H8. This work discusses the objectives, design details and mission concept of operations of the GARI spectrometers.
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