Detector characteristics detective quantum efficiency

The first two-dimensional detector in X-ray diffraction was conventional film. It remained for decades the detector of choice for both single crystal as well as powder diffraction experiments. In the field of two-dimensional detection it was surpassed initially by image plates and later by CCD cameras (Figure 14.1). Today virtually no film is in use, with perhaps the exception of Polaroid used for single-crystal images. To be able to compare various detectors with one another, and to select the most appropriate detector for a specific experiment, certain key technical qualities are important. These are in general the detective quantum efficiency, the spatial response characteristics, the size, speed and dynamic range. ... 

An important characteristic of any detector is how efficiently it collects x-ray photons and then converts them into a measurable signal. Detector efficiency is determined by first, a fi-action of x-ray photons that pass through the detector window (the higher, the better) and second, a fraction of photons that are absorbed by the detector and thus result in a series of detectable events (again, the higher, the better). The product of the two fractions, which is known as the absorption or quantum efficiency, should usually be between 0.5 and 1. 

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