Monte-Carlo simulations of the background noise in gamma-ray satellites

Abstract

Monte Carlo simulations are used in g-ray astronomy to estimate the effects of the space radiation environment to which the detectors onboard satellites are exposed. A study of a sample of Classical Novae using the BATSE (Burst and Transient Source Experiment) Earth Occultation Technique shows the sensitivity to be degraded by systematic effects. By modelling the instrument background, however, the sensitivity could be improved significantly. Simulations of the background noise in the LEGRI detectors are able to predict the observed effects of geomagnetic cut-off on the cosmic ray and atmosphere background components. The background spectra are dominated by fluorescence from the tantalum collimator. The effects of a passage through the South Atlantic Anomaly are modelled and compared to observations. Activation of spacecraft components causes a decay of the background count rate with time. The main contributions to the induced background noise are shown to be the collimator, cadmium telluride and shielding. No single isotope explains the observed decay time of the background. Similar methods have been used to model the effect of a solar flare on the instruments onboard the INTEGRAL satellite. The count rates in the detectors are found to increase significantly for periods of up to 96 hours after the flare. Many line features can be seen in the spectra and these are found to be mainly due to electron capture processes within the detectors.

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