Measured radiation damage in charge coupled devices exposed to simulated deep orbit proton fluxes

Measurements were made to quantify the effects of radiation damage in large area, deep-depletion CCDs developed for the joint European X-ray telescope (JET-X). Two devices were tested — the first, a standard X-ray CCD and the second, otherwise identical, including supplementary buried channels to improve its radiation hardness. Both devices were exposed to the expected in-orbit proton fluxes at the proton irradiation facility (PIF) at the Paul Scherrer Institute. The experimental conditions included the predicted orbital energy spectrum, its evolution and the proposed JET-X proton shielding. Energy resolution and charge transfer efficiency were measured after exposure to incremental doses corresponding to 0.25, 0.5, 1, 2 and 5 years in orbit. The radiation-hard device performed substantially better than the conventional device, showing a 20% degradation in energy resolution after 5 years equivalent dose (corresponding to ∼ 109 protons cm−2), as compared to ∼ 60% for the conventional device. Finally, the devices were exposed to fluences appropriate to the August 1972 solar flare. These results have been used to develop a model to predict the fwhm energy resolution of radiation damaged CCD.