IONIZATION CHAMBER

IONIZATION CHAMBER Radiation Detectors IONIZATION CHAMBER The ionization chamber is a detector that operates in the ionization region. EO 2.3 DESCRIBE the operation of an ionization chamber to include: a. Radiation detection b. Voltage variations c. Gamma sensitivity reduction 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 have two distinct disadvantages when compared to proportional counters: they are less sensitive, and they have a slower response time. There are two types of ionization chambers to be discussed: the pulse counting ionization chamber and the integrating ionization chamber. In the pulse counting ionization chamber, the pulses are detected due to particles traversing the chamber. In the integrating chamber, the pulses add, and the integrated total of the ionizations produced in a predetermined period of time is measured. The same type of ionization chamber may be used for either function. However, as a general rule, the integrating type ionization chamber is used. Flat plates or concentric cylinders may be utilized in the construction of an ionization chamber. The flat plate design is preferred because it has a well-defined active volume and ensures that ions will not collect on the insulators and cause a distortion of the electric field. The concentric cylinder design does not have a well-defined active volume because of the variation in the electric field as the insulator is approached. Ionization chamber construction differs from the proportional counter (flat plates or concentric cylinders vice a cylinder and central electrode) to allow for the integration of pulses produced by the incident radiation. The proportional counter would require such exact control of the electric field between the electrodes that it would not be practical. IC-06 Page 28 Rev. 0