Detectors for Electron and X-ray Scattering and Imaging Experiments

Abstract

Suitable detectors for these expensive and highly complex experimental instruments described in the previous chapters are a key factor to consider, primarily because if one cannot visualize or record the experimental results with an appropriate detector, any experiment will fail. The general challenge for all position-, energy-, and time-resolving detector systems is the fulfillment of stringent requirements for direct X-ray and electron detection experiments. These include a priori a high detection sensitivity and efficiency, but most important is coping with extremely high flux (10¹² highly energetic X-ray photons or 10⁸ 300 kV electrons per second), exhibiting appropriate radiation hardness to maintain proper detection sensitivity and operability, low electronic noise for finest energy resolution in single-photon counting mode, and high frame rates for high time resolution. Parameters such as the Modulation Transfer Function (MTF), the Detector Quantum Efficiency (DQE), the dynamic range, pixel size, sensitivity, linearity, uniformity, background noise, read out speed, and reliability (or life time) among other characteristics will need to be considered to decide which detector design is best for what application. There are a variety of designs in the development and/or prototype stage. Costs are high, because most are produced using expensive wafer fabrication processes. A point of consideration is flexibility, adaptability, and how swift detector parameters can be changed. The trend at high-end, multi-national, multi-user scientific research facilities (Synchrotrons, FELs) however, is to operate dedicated, non-transferable detectors for specialized applications, whereas the medium to small scale research facilities may well decide for a more versatile, multi-purpose detector. The following sections will address detectors for electrons and detectors for X-ray photons separately. Development efforts for these detector types overlap, in part due to the high costs involved, and in part due to the compatibility of some developmental stages and components for both detector types.