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Ionization chambers
General principles of operation, depending on the sensitivity of radiation detectors, ionization chambers, the energy of the radiation.
Instrument (gauge) with an ionization chamber consists of a camera to one internal and one external electrodes, a voltage source, the system display (indicating instrument) G and measuring resistor R or measuring capacitor C (Fig. 1). Ionization current (flux or dose) was determined by measuring the voltage drop in the high resistor R. Measurement of the charge as the time integral of current (flow measurement or dose) is defined charging capacitor C.
Depending on the required sensitivity and geometric adjustment to set the measuring task using various ionization chambers. Measuring range detectors operate on the principle of the ionization chamber, covers the value of shares to thousands mikrogreya Gray (from mkGy / h to kGy / h).
When filling the air ionization chambers are suitable as defined for measuring the ion dose. However, it is necessary to use special design, eliminating or offsetting effect of the walls of the ionization chamber, limiting the volume of air. For practical measurements developed many measuring chambers. In their application, along with a sensitivity range of measurement and reproducibility of the results must take into consideration the following points.
1. Dependence of the sensitivity of the energy shows the extent to which the measured value depends on the energy of the radiation. Typical examples of the energy dependence of different types of radiation detectors are shown in Figure 2.
2. Dependence of the sensitivity of the direction of flight of the particles (rays) is due to the very design of the detector. Depending on the direction of incidence is necessary to introduce amendments, which, in turn, may depend on the energy of the radiation.
3. Dependence of the sensitivity of the temperature and pressure is shown in the fact that the systems unsealed ionization chamber calculated mass changes with temperature and air pressure. This also necessitates a correction factor, which must be multiplied to obtain the correct reading of measured values, if the sensitivity of the measuring system was not set up in advance by the reference current.
Fig. 1. Schematic diagram of the ionization chamber to measure the dose rate or the absorbed dose
Fig. 2. Typical dependence of the sensitivity of various radiation detectors from the energy level (mean values for a large number of individual devices are shown in parentheses, and any variations in the critical region, matching the results of measurements performed Burckhardt and Pisz:
OM - Geiger-Muller, IK - ionization chamber; CZ - scintillation counter-tion, DIK - high-pressure ionization chamber
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