Signal Processing for Radiation Detectors

Mohammad Nakhostin

• Publisher: Wiley
• Year: 2017
• ISBN:
  9781119410164
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Signale & Signalverarbeitung

Presents the fundamental concepts of signal processing for all application areas of ionizing radiation

This book provides a clear understanding of the principles of signal processing of radiation detectors. It puts great emphasis on the characteristics of pulses from various types of detectors and offers a full overview on the basic concepts required to understand detector signal processing systems and pulse processing techniques. Signal Processing for Radiation Detectors covers all of the important aspects of signal processing, including energy spectroscopy, timing measurements, position-sensing, pulse-shape discrimination, and radiation intensity measurement.

The book encompasses a wide range of applications so that readers from different disciplines can benefit from all of the information. In addition, this resource:

• Describes both analog and digital techniques of signal processing
• Presents a complete compilation of digital pulse processing algorithms
• Extrapolates content from more than 700 references covering classic papers as well as those of today
• Demonstrates concepts with more than 340 original illustrations

Signal Processing for Radiation Detectors provides researchers, engineers, and graduate students working in disciplines such as nuclear physics and engineering, environmental and biomedical engineering, and medical physics and radiological science, the knowledge to design their own systems, optimize available systems or to set up new experiments.

1
Signal Generation in Radiation Detectors

Understanding pulse formation mechanisms in radiation detectors is necessary for the design and optimization of pulse processing systems that aim to extract different information such as energy, timing, position, or the type of incident particles from detector pulses. In this chapter, after a brief introduction on the different types of radiation detectors, the pulse formation mechanisms in the most common types of radiation detectors are reviewed, and the characteristics of detectors’ pulses are discussed.

1.1 Detector Types

A radiation detector is a device used to detect radiation such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator. In addition to detecting the presence of radiation, modern detectors are also used to measure other attributes such as the energy spectrum, the relative timing between events, and the position of radiation interaction with the detector. In general, there are two types of radiation detectors: passive and active detectors. Passive detectors do not require an external source of energy and accumulate information on incident particles over the entire course of their exposure. Examples of passive radiation detectors are thermoluminescent and nuclear track detectors. Active detectors require an external energy source and produce output signals that can be used to extract information about radiation in real time. Among active detectors, gaseous, semiconductor, and scintillation detectors are the most widely used detectors in applications ranging from industrial and medical imaging to nuclear physics research. These detectors deliver at their output an electric signal as a short current pulse whenever ionizing radiation interacts with their sensitive region. There are generally two different modes of measuring the output signals of active detectors: current mode and pulse mode. In the current mode operation, one only simply measures the total output electrical current from the detector and ignores the pulse nature of the signal. This is simple but does not allow advantage to be taken of the timing and amplitude information that is present in the signal. In the pulse mode operation, one observes and counts the individual pulses generated by the particles. The pulse mode operation always gives superior performance in terms of the amount of information that can be extracted from the pulses but cannot be used if the rate of events is too large. Most of this book deals with the operation of detectors in pulse mode though the operation of detectors in current mode is also discussed in Chapter 5. The principle of pulse generation in gaseous and semiconductor detectors, sometimes known as ionization detectors, is quite similar and is based on the induction of electric current pulses on the detectors’ electrodes. The pulse formation mechanism in scintillation detectors involves the entirely different physical process of producing light in the detector. The light is then converted to an electric current pulse by using a photodetector. In the next sections, we discuss the operation of ionization detectors followed by a review of pulse generation in scintillation detectors and different types of photodetectors.

1.2 Signal Induction Mechanism

1.2.1 Principles

In gaseous and semiconductor detectors, an interaction of radiation with the detector’s sensitive volume produces free charge carriers. In a gaseous detector, the charge carriers are electrons and positive ions, while in the semiconductor detectors electrons and holes are produced as result of radiation interaction with the detection medium. In such detectors, an electric field is maintained in the detection medium by means of an external power supply. Under the influence of the external electric field, the charge carriers move toward the electrodes, electrons toward the anode(s), and holes or positive ions toward the cathode(s). The drift of charge carriers leads to the induction of an electric pulse on the electrodes, which can be then read out by a proper electronics system for further processing. To understand the physics of pulse induction, first consider a charge q near a single conductor as shown in Figure 1.1. The electric force of the charge causes a separation of the free internal charges in the conductor, which results in a charge distribution of opposite sign on the surface of the conductor. The geometrical distribution of the induced surface charge depends on the position of the external charge q with respect to the conductor. When the charge moves, the geometry of charge conductor changes, and therefore, the distribut...