Automatic Control System An automatic control system is a preset closed-loop control system that requires no operator action. This assumes the process remains in the normal range for the control system. An automatic control system has two process variables associated with it: a controlled variable and a manipulated variable. A controlled variable is the process [...]
Electron-Ion Pair Ionization is the process of removing one or more electrons from a neutral atom. This results in the loss of units of negative charge by the affected atom. The atom becomes electrically positive (a positive ion). The products of a single ionizing event are called an electron-ion pair. Specific Ionization Specific ionization is [...]
Neutron Neutrons have no electrical charge and have nearly the same mass as a proton (a hydrogen atom nucleus). A neutron is hundreds of times larger than an electron, but one quarter the size of an alpha particle. The source of neutrons is primarily nuclear reactions, such as fission, but they are also produced from [...]
Gamma Ray The gamma ray is a photon of electromagnetic radiation with a very short wavelength and high energy. It is emitted from an unstable atomic nucleus and has high penetrating power. There are three methods of attenuating (reducing the energy level of) gamma-rays: photoelectric effect, compton scattering, and pair production. The photoelectric effect occurs [...]
Alpha Particle The alpha particle is a helium nucleus produced from the radioactive decay of heavy metals and some nuclear reactions. Alpha decay often occurs among nuclei that have a favorable neutron/proton ratio, but contain too many nucleons for stability. The alpha particle is a massive particle consisting of an assembly of two protons and [...]
The pulsed operation of the gas-filled detector illustrates the principles of basic radiation detection. Gases are used in radiation detectors since their ionized particles can travel more freely than those of a liquid or a solid. Typical gases used in detectors are argon and helium, although boron-triflouride is utilized when the detector is to be [...]
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 [...]
A proportional counter is a detector which operates in the proportional region, as shown in Figure 6. Figure 7 illustrates a simplified proportional counter circuit. To be able to detect a single particle, the number of ions produced must be increased. As voltage is increased into the proportional region, the primary ions acquire enough energy [...]
Proportional counters measure the charge produced by each particle of radiation. To make full use of the counter’s capabilities, it is necessary to measure the number of pulses and the charge in each pulse. Figure 9 shows a typical circuit used to make such measurements. The capacitor converts the charge pulse to a voltage pulse. [...]
Ionization chambers are electrical devices that detect radiation when the voltage is adjusted so that the conditions correspond to the ionization region (refer to Region II of Figure 6). The charge obtained is the result of collecting the ions produced by radiation. This charge will depend on the type of radiation being detected. Ionization chambers [...]
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