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Different ranges of applied voltage result in unique detection characteristics. EO 1.5 Given a diagram of an ion pairs collected -vs- detector voltage curve, DESCRIBE the regions of the curve to include: a. The name of the region b. Interactions taking place within the gas of the detector c. Difference between the alpha and beta curves, where applicable Applied Voltage The relationship between the applied voltage and pulse height in a detector is very complex. Pulse height and the number of ion pairs collected are directly related. Figure 6 illustrates ion pairs collected -vs- applied voltage. Two curves are shown: one curve for alpha particles and one curve for beta particles; each curve is divided into several voltage regions. The alpha curve is higher than the beta curve from Region I to part of Region IV due to the larger number of ion pairs produced by the initial reaction of the incident radiation. An alpha particle will create more ion pairs than a beta since the alpha has a much greater mass. The difference in mass is negated once the detector voltage is increased to Region IV since the detector completely discharges with each initiating event.
Figure 6 Ion Pairs Collected -vs- Applied Voltage
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