Radiation Damage Effects on X-Ray Detectors for Future Planetary and Astronomy Missions

This thesis describes both theoretical and experimental work conducted to further develop X-ray instrumentation for future planetary and astronomy space missions. Such instruments are used to probe, ever deeper, the high energy Universe; from black holes and active galactic nuclei, to supernovae, galaxy formation and clusters. X-rays can also be used to establish the elemental composition of planetary surfaces from orbit or in situ, furthering our understanding of planetary and moon formation in our solar system. Chapter 1 introduces X-ray instrumentation and uses the International X-ray Observatory as a case study to explore the many new developments in X-ray instrumentation, both in optics and detectors. Chapter 2 further explores the field of X-ray optics, particularly the novel Microchannel Plate Optics used on the BepiColombo Mercury Imaging X-ray Spectrometer, MIXS. The characterisation of an MCP optic is presented, demonstrating the best angular resolution measurement of a flat square-pore square-packed Microchannel Plate Optic to date; <2 arcminutes FWHM resolution. Chapter 3 moves from the X-ray optics used on BepiColombo MIXS to the detectors used in the instrument focal plane; Active Pixel Sensor Depleted Field Effect Transistors (DEPFETs). The solar proton radiation environment around Mercury is one of the most damaging in the solar system due to its proximity to the sun, with ~3x1010 10 MeV equivalent solar protons expected over the mission lifetime. This Chapter presents the proton radiation damage experiments conducted at the Birmingham University Cyclotron, establishing the current related damage rate, α, and dark current increase that can be expected from this radiation damage. The design of the MIXS instrument was changed to include an annealing capability based on the findings of the experiment presented here. A follow-up proton irradiation experiment carried out at the University of Technology in Munich, in collaboration with the Max Planck Institute’s Semiconductor Laboratory (MPE-HLL) is also discussed. Chapters 4 and 5 present the experimental and modelling work carried out in the investigation of X-ray CCDs which, to date, have been the X-ray detectors of choice for many space and terrestrial applications. The aim of this work was to improve the quantum efficiency and spectral resolution of the CCD66, a novel CCD structure initially designed with applications such as the Wide Field Imager of the International X-ray Observatory in mind, by direct manipulation of the device depletion region by applying a negative substrate voltage. Modelling work was also undertaken to investigate the effect of X-ray angle of incidence on spectral resolution and quantum efficiency. The future of X-ray astronomy and planetary science depends heavily on advances in optics and detector technology. The work presented in this thesis show incremental, yet mission-enabling developments for X-ray instruments likely to fly in the future such as BepiColombo’s Mercury Imaging X-ray Spectrometer.