Пропорционал санауыш детекторы және оның қолданылуы

Gaseous ionization detector
The proportional counter is a type of gaseous ionization detector device used to measure particles of ionizing radiation. The key feature is its ability to measure the energy of incident radiation, by producing a detector output pulse that is proportional to the radiation energy absorbed by the detector due to an ionizing event; hence the detector's name. It is widely used where energy levels of incident radiation must be known, such as in the discrimination between alpha and beta particles, or accurate measurement of X ray radiation dose. A proportional counter uses a combination of the mechanisms of a Geiger–Müller tube and an ionization chamber, and operates in an intermediate voltage region between these. The accompanying plot shows the proportional counter operating voltage region for a co axial cylinder arrangement.

Usually the detector is filled with a noble gas; they have the lowest ionization voltages and do not degrade chemically. Typically neon, argon, krypton or xenon are used. Low energy x rays are best detected with lighter nuclei (neon), which are less sensitive to higher energy photons. Krypton or xenon are chosen when for higher energy x rays or for higher desired efficiency. Often the main gas is mixed with a quenching additive. A popular mixture is P10 (10% methane, 90% argon). Typical working pressure is 1 atmosphere (about 100 kPa).

The proportionality between the energy of the charged particle traveling through the chamber and the total charge created makes proportional counters useful for charged particle spectroscopy. By measuring the total charge (time integral of the electric current) between the electrodes, we can determine the particle's kinetic energy because the number of ion pairs created by the incident ionizing charged particle is proportional to its energy. The energy resolution of a proportional counter, however, is limited because both the initial ionization event and the subsequent 'multiplication' event are subject to statistical fluctuations characterized by a standard deviation equal to the square root of the average number formed. However, in practice these are not as great as would be predicted due to the effect of the empirical Fano factor which reduces these fluctuations. This covers all radiation instrument technologies and is a useful comparative guide to the use of proportional counters.