Nuclear spallation by solar proton events and cosmic rays in the eROSITA and ATHENA focal plane configurations

Soft protons can be a major source of degradation of the performances of instrumentation in space, in particular for CCDs. It was learned from the experience of Chandra and XMM-Newton that they can be funneled through the mirrorshells of an X-ray telescope down to the focal plane and hit detectors. This seems the favoured mechanism, since in general a detector placed at the focal plane is completely shielded from environmental soft protons except that in correspondance of the aperture field of view. However, the bombardment of high-energy cosmic rays can induce spallation reactions in the shield itself and other materials present at the focal plane. These processes generate secondary hadrons at softer energy, which can escape the target and reach the detectors. The products of spallation are mainly protons and neutrons. Neutrons can also have an impact on the performances of a Silicon-based detector. We study the production of secondary hadrons in the case of the pn-CCDs aboard eROSITA and the DEPFET Wide Field Imager aboard ATHENA, calculate expected doses over the missions duration and discuss possible effects on these detectors.