Status of instrumental background simulations for gamma-ray telescopes with Geant4

Hard X-ray and low-to-medium-energy gamma-ray telescopes may be exposed to many different types of background radiation ranging from cosmic rays to secondary particles from Earth’s atmosphere and charged particles trapped in radiation belts. Due to low source count rates in this energy regime, the background will dominate the source signal in many cases, in some up to a factor of 100. Therefore reliable Monte Carlo simulations of the background are extremely important to understand the recorded data and to predict the performance of future telescopes. We report on the status of the development and verification of a Geant4-based tool to simulate those background components, especially the resulting detector activation due to hadron interactions, as a successor to MGGPOD. Initial comparisons between simulations and background measurements of the TGRS detector are promising: Geant4 can reproduce the shape of the background to an accuracy better than 20%. In addition, many of the nuclear activation lines seen in the measurements are also present in the simulations — although there is still room for improvement especially with respect to the agreement of the line intensities.