Detector efficiency, linearity, proportionality and resolution

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. 

The efficiency of modem detectors is quite high, in contrast to the x-ray film, which requires multiple photons to activate a single grain of photon-sensitive silver halide. It is important to keep in mind that the efficiency depends on the t3qie of the detector and it normally varies with the wavelength for the same type of the detector. The need for high efficiency is difficult to overestimate since every missed (i.e. not absorbed by the detector) photon is simply a lost photon. It is nearly impossible to account for the lost photons by any amplification method, no matter how far the amplification algorithm has been advanced. 

The linearity of the detector is critical in obtaining correct intensity measurements (photon count). The detector is considered linear when there 

For the purpose of this consideration, the dynamic range is the ability of the detector to count photons at both the low and high fluxes with the same effectiveness, and by the background noise we mean the events similar to those generated by the absorbed photons, but occurring randomly and spontaneously in the detector without photons entering the detector. 

Proportional 5% Good, but fails at high photon flux 14% 26 310 

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