TABLE OF CONTENTS The investigation of nuclear and particle collisions or disintegrations relies upon detectors for measuring the products of such interactions. Although subatomic particles are certainly too small to be observed through purely visual means, we can use the mechanisms for energy deposition we described in the previous chapter to detect such particles. Although we will describe only the very simplest prototype detectors, the principles underlying their performance are similar to those used in even the most sophisticated devices.
Ionization detectors are devices designed to measure the ionization produced when an incident particle traverses some medium. If the number of detected electrons and positive ions is to reflect the energy deposited in the material, then any produced electron-ion pairs must be kept from immediately recombining into atoms. This can be done by applying a sufficiently high electric field across the medium. This field will separate the charges, start their drift towards their respective electrodes, and thereby keep them from recombining.
The basic ionization detector consists of a chamber that is filled with a suitable medium that can be easily ionized. The chamber has a cathode and an anode that are held at some large relative voltage, and the device is characterized by a capacitance (C) that is determined by the geometry of the electrodes. The operating medium should be chemically stable (or inert) so that the moving ionization electrons are not easily captured by the molecules of that medium. The medium should not be...
