Speaker
Description
Summary
The MXGS instrument is a spectrometer based on a 576 cm2 CdZnTe (5 mm thickness)
pixellated detector plane optimized for the energy range from 10 up to 500 keV. The
MXGS main scientific objective consists on the study of the Earth atmosphere gamma
ray burst, so called Terrestrial Gamma-ray Flashes (TGF) (Nemiroff et al.,1997).
The TGF expected to be observed at the ISS is 5 ms. Burst with a fluence of
ph/cm2/msec/keV similar to those derived from the analysis of RHESSI data. Therefore,
the MXGS sensitivity will be determined by the environment background at the ISS orbit.
The ISS environment has been simulated using the SPENVIS (ESA) and the CREME96 (NRL)
tools. Decay products have been simulated using the Geant4 toolkit.
The cosmic proton flux has been simulated using CREME96 assuming a solar quiet model
(absence of flares) during a solar minimum period. The integrated flux (orbit
average) for the cosmic protons source in the detector is 0.14 counts/cm2/sec.
Trapped particles have been simulated using SPENVIS having as inputs the AP8-MIN and
AE8-MIN trapped particle models. The main conclusion is that MXGS will be under a
very high flux of trapped particles 20% of orbital time.
Protons dominates background spectra with an expected count rate from 3000 counts for
deeper South Atlantic Anomaly (SAA) crossing to 8-5 counts for marginal SAA passes.
The remaining components of background, like electrons and photons, are responsible
of less than 20% of the expected count rate.
Finally, these preliminary results have been obtained in the ASIM mission Phase A.
The current objective, to be performed during mission Phase B) is to identify the
decay products from the inputs simulated in GEANT4 and to perform a detailed MXGS
background model.
