Signal Processing for Radiation Detectors

8Pulse‐Shape Discrimination

Sensing differences in the shape of output pulses from a radiation detector may provide valuable information on the radiation striking on the detector. The pulse‐shape information can be used to identify the type of radiation, reduce the background events, discriminate between particles of different range, discard defective pulses, and so on. In this chapter, we review the common analog methods of pulse‐shape discrimination. The digital methods will be discussed in Chapter 10.

8.1 Principles of Pulse‐Shape Discrimination

8.1.1 Ionization Detectors

In Chapter 1, it was discussed that the shape of a current pulse from an ionization‐type detector, that is, gaseous and semiconductor detectors, due to a point‐like ionization can be described by the Shockley–Ramo theorem as

(8.1)

where Q denotes the ionization charge, v is the drift velocity, E_w is the weighting field, x(t) is the position, and the negative and positive subscripts denote the electron and holes or positive ions, respectively. The current pulse generated by an extended ionization can also be obtained as a superposition of current contributions from point‐like ionizations that form the ionization track. The corresponding charge pulse is given by an integration of induced current during the charge collection time. The parameters involved in the pulse formation indicate that the shape of output ...