3.5.5. X-Ray Detectors in WDS Analysis

Detectors convert X-rays photons through ionization into voltage pulses which can be counted. There are four types of detectors used in microprobes: gas-flow proportional and sealed-gas proportional, scintillation - photomultiplier (PM), and semiconductor (discussed until EDS analysis). The first three types have poor energy discrimination and are used for detection of monochromatic X-rays, where an analyzing crystal has "preselected" the X-ray energy.

In a "proportional" counter the size of pulse is proportional to the energy of the X-ray that produced it. This permits voltage discrimination using a single channel analyzer (SCA) to perform pulse height analysis. An SCA can exclude all but a narrow range of voltage pulses to be sent on the counting circuitry (effectively, discriminating against unwanted X-rays). All detectors suffer from deadtime due to the physical constraints on X-ray detection.