Quantum efficiency , signal detector

Sandborg, M. and G. Alm-Carlsson, Influence of x-ray energy spectrum, contrasting detail and detector on the signal-to-noise ratio (SNR) and detective quantum efficiency (DQE) in projection radiography. Phys. Med. Biol., 1992. 37(6) p. 1245-1263. 

Figure 5 Basic steps in a CL process (a) the sample and reagent(s) are introduced in the reaction cell and the final reagent is injected to initiate the CL emission, then light is monitored by the detector (b) curve showing CL intensity as a function of time after reagent mixing to initiate the reaction (the decay of the signal is due to the consumption of reagents and changes in the CL quantum efficiency with time) (c) a calibration function is established in relation to increasing analyte concentrations.

The most recent advance in ROA instrumentation is the use of charge coupled device (CCD) detectors [86,87]. These detectors have extremely low background noise, large areas, and very high quantum efficiency (in the range of 25 to 80%). The use of these detectors in ROA measurements has given rise to a renaissance in this field. Applications that were previously impossible due to low signal quality have now become almost routine. 

Quantum Efficiency, Q. Probability that a photon striking the detector generates an electronically measurable signal, usually a photoelectron. Units are photoelectrons/photon, often stated as a percentage. 

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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