The low Earth orbit radiation environment and its impact on the prompt background of hard x-ray focusing telescopes

摘要

The background minimization is a science-driven necessity in order to reach deep sensitivity levels in the hardX-ray band, one of the key scientific requirements for hard X-ray telescopes (e.g. NuSTAR, ASTRO-H). Itrequires a careful modeling of the radiation environment and new concepts of shielding systems. We exploitthe Bologna Geant4 Multi-Mission Simulator (BoGEMMS) features to evaluate the impact of the Low EarthOrbit (LEO) radiation environment on the prompt background level for a hybrid Si/CdTe soft and hard X-raydetection assembly and a combined active and passive shielding system. For each class of particles, the spectraldistribution of the background flux is simulated, exploring the effect of different materials (plastic vs inorganicactive scintillator) and configurations (passive absorbers enclosing or surrounded by the active shielding) onthe background count rate. While protons are efficiently removed by the active shielding, an external passiveshielding causes the albedo electrons and positrons to be the primary source of background. Albedo neutronsare instead weakly interactive with the active shielding, and they cause an intense background level below 10keV via elastic scattering. The best shielding configuration in terms of background and active shielding countrates is given by an inorganic scintillator placed inside the passive layers, with the addition of passive materialto absorb the intense fluorescence lines of the active shielding and avoid escape peaks on the CdTe detector.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.