Dr
Valentina Fioretti
(INAF/IASF Bologna)
Low energy protons (< 300 keV) can enter the field of view of X-ray space telescopes, scatter at small incident angles, and deposit energy on the detector. This phenomenon can cause intense background flares at the focal plane decreasing the mission observing time (e.g. the XMM-Newton mission) or in the most extreme cases, damaging the X-ray detector. Among the many physical processes that have been proposed to describe the scattering of soft protons by X-ray optics, only the Coulomb single and multiple scattering models are currently available in the official Geant4 toolkit.
Under the AREMBES (ATHENA Radiation Environment Models and X-Ray Background Effects Simulators) development activities, a new physics model (“the Remizovich scattering”) is implemented, verified, and qualitatively validated on top of the Geant4 release 10.2. Both the new scattering physics and the Coulomb scattering already built in the official Geant4 distribution are used to reproduce the latest experimental results on grazing angle proton scattering.
Since the experimental data are not completely representative of the soft proton scattering experienced by current X-ray telescopes, we are not able to address any of the tested models as the one that can certainly reproduce the scattering behavior of low energy protons expected for the ATHENA mission. We can, however, discard multiple scattering as the model able to reproduce soft proton funnelling, and affirm that Coulomb single scattering can represent, until further measurements at lower energies, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.
Summary
Under the AREMBES (ATHENA Radiation Environment Models and X-Ray Background Effects Simulators) development activities, a new physics model (“the Remizovich scattering”) is implemented on top of the Geant4 release 10.2 to describe low energy (<300 keV) proton scattering at glancing angles by the optics of X-ray space missions. Both the new scattering physics and the Coulomb scattering already built in the official Geant4 distribution are used to reproduce the latest experimental results on grazing angle proton scattering. We can discard multiple scattering as the model able to reproduce soft proton funnelling, and affirm that Coulomb single scattering can represent, until further measurements at lower energies, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.
