Measurements of the soft proton reflectivity on x-ray optics

Orbital soft protons that reach the detector region of astronomical X-ray observatories can seriously degrade the instrumental performance. Firstly, they pose a non-reducible background component and, secondly, they might induce permanent damage in the sensors. A reliable performance estimation and risk assessment for new X-ray missions is only possible when radiation transport simulations are based on and validated against experimental scattering data.

In order to address this need for experimental data, we conducted measurement campaigns at various accelerator facilities and at different energies below 1 MeV in the past decade. Targets ranged from classic gold-coated nickel shells as used for the optics of XMM-Newton and eROSITA to the latest silicon pore optics (SPO) samples coated with iridium as foreseen for Athena.

The latest measurements with SPO samples were taken with a completely new experimental design at considerably lower energies than before, ranging from 20 keV to 50 keV, and with an MCP detector that features two dimensional position resolution. Therefore, this data is even more relevant for background studies and features a much finer angular coverage. Furthermore, the data yield hints that a significant fraction of scattered protons undergoes charge exchange and, thus, is not affected by a magnetic diverter.

In this contribution, we give an overview of the different proton experiments and their results and present our new low-energy setup together with some preliminary results.