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G. Weidenspointner, M. Harris (NASA/GSFC and USRA), C. Ferguson (University of Southampton, UK), S. Sturner, C. Shrader (NASA/GSFC and USRA), B. Teegarden (NASA/GSFC), R. Diehl, C. Wunderer (MPE, Germany)
High instrumental backgrounds are a notorious problem for low-energy gamma-ray astronomy. We have developed MGGPOD, a suite of Monte Carlo codes built around the widely used GEANT (Version 3.21) package, to simulate ab initio the physical processes relevant for the production of instrumental backgrounds. These include the build-up and delayed decay of radioactive isotopes as well as the prompt de-excitation of excited nuclei, both of which give rise to a plethora of instrumental gamma-ray background lines in addition to continuum backgrounds. We demonstrate the capabilities of the MGGPOD suite by modelling high resolution gamma-ray spectra recorded by the Transient Gamma-Ray Spectrometer (TGRS) on board Wind and the SPI spectrometer on the recently launched INTEGRAL observatory. These data reveal the complex instrumental backgrounds in formidable detail, particularly the many gamma-ray lines produced in the detector and spacecraft materials by cosmic-ray interactions. We report the successes (and failures) of the MGGPOD codes in reproducing the "dark sides" of TGRS and SPI.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.