Enhanced soft X-ray detection efficiencies for imaging microchannel plate detectors

Abstract

Position-sensitive detectors using microchannel plate (MCP) electron multipliers have been widely used in X-ray astronomy1–3. Although MCPs facilitate X-ray imaging with high spatial resolution, as on the Einstein1 or EXOSAT3 satellites, their intrinsic soft X-ray detection efficiencies are low. These lie typically in the range 1–10% (ref. 4), much lower than the (near unity) values attainable with competing forms of gas proportional counter. To enhance sensitivity to X-ray energies below a few keV, a material of relatively high photoelectric yield may be deposited on the MCP front surface and channel walls. MgF2 has commonly fulfilled this role for X-ray astronomy1–3, resulting in enhanced efficiencies 1.1–1.6 times those of uncoated MCPs1. We report here high 0.18–1.5 keV X-ray detection efficiencies for MCPs bearing CsI deposition photocathodes. Efficiency enhancement factors, dependent on X-ray incident angle, of up to 15 times have been stably obtained. The importance of this work for the sensitivity of future X-ray astronomy experiments, such as the Rontgensatellit (ROSAT) Wide Field Camera, is outlined.