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In this article we introduce the low-energy CZT (CdZnTe) 16 384-pixel detector array on-board the Atmosphere Space Interaction Monitor (ASIM), funded by the European Space Agency. This detector is a part of the larger Modular X-and Gamma-ray sensor (MXGS). The CZT detector array is sensitive to photons with energies between 15 keV and 400 keV. The principal objective of the MXGS instrument is to detect Terrestrial Gamma ray Flashes (TGFs), which are related to thunderstorm activity. The concept of the detector array is presented, together with brief descriptions of its mechanical structure and electronics. A method for detector characterization is outlined and preliminary experimental results are shown.

This paper presents the Bismuth Germanate Oxide (BGO) front-end electronics design and signal processing in Modular X- and Gamma ray sensor (MXGS) instrument onboard the Atmosphere Space Interaction Monitor (ASIM) mission, funded by the European Space Agency. University of Bergen is responsible for the design and development of the detector layers and readout electronics for the MXGS instrument. The principal objective of the instrument is to detect Terrestrial Gamma ray Flashes (TGFs), which are related to thunderstorm activity. The digital pulse processing scheme used in the MXGS BGO detector gives it a significantly higher rate capability than what has been achieved in other instruments used in the study of terrestrial gamma flashes. The front-end electronics for the BGO detector layer in MXGS system also uses fewer components compared to conventional analog front-ends for BGO detectors, thereby increasing its reliability and projected lifetime in the harsh space environment. The MXGS instrument is expected to see about 1000 TGFs in a time period of one year.

The National Space Institute, Technical University of Denmark is responsible for the selection and characterization of the CZT detector crystals for the X and gamma -ray instrument MXGS onboard ESA’s Atmospheric Space Interaction Monitor (ASIM) mission. The Modular X- and Gamma ray Sensor (MXGS) shall, situated on the International Space Station, detect Terrestrial Gamma ray Flashes (TGF) generated in the Earth atmosphere. TGFs are believed to be produced in connection with thunderstorms and ASIM will therefore also be equipped with optical instruments which trigger on lightening.

In this paper, charge sharing and charge loss effects in pixilated CZT/CdTe detectors are investigated by measurements. We measured charge sharing effects function of the inter-pixel gap (with same pixel pitch), the photon energy and the detector bias voltage for a large numbers of CZT and CdTe pixel detector samples. The results are used for the development of the large area X-ray and Gamma ray detector for the Atmosphere-Space Interactions Monitor (ASIM) planned for the ISS ESA Columbus module. Charge sharing measurements on detector samples with identical size and pixel geometry with different inter-pixel gap showed charge loss on the gap surface which is linear dependent on gap size.