Effect of low-energy protons on the performance of the EPIC pn-CCD detector on XMM-Newton

Abstract

After the launch of Chandra, it was realized that low energy protons (below approximately 300 keV) are funnelled by grazing incident mirrors onto the focal plane detectors. Front illuminated CCD detectors are very sensitive to soft protons causing radiation damage in their electrode structures and transfer channels. The back-illuminated 280 micrometer thick fully depleted pn-CCD of the European Photon Imaging Camera (EPIC) on board the X-ray Multi Mirror mission (XMM) is by far less sensitive to low energy proton radiation. Commanding the camera in a special low gain mode, even allows to directly measure proton spectra and event patterns up to 300 keV per pixel. At the 3 MV Van-de-Graaff accelerator of the Institute for Physics in Tubingen we have irradiated and tested a 3 cm2 flight-like pn-CCD with protons from 1 to 300 keV up to a fluence of 1.4 (DOT) 109 protons/cm2. This is about a factor of 1000 above the expected solar proton fluence for a 10 year XMM-Newton mission under nominal operational conditions. In this paper we given an overview of the proton irradiation experiment, discuss the performance of the detector after proton irradiation and finally present proton spectra directly measured with the pn-CCD on board XMM-Newton during solar flares. In addition, we briefly describe the precautionary measures taken to minimize the proton radiation dose of the EPIC CCD detectors in orbit.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.