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
