PROPORTIONAL COUNTER

Radiation Detectors PROPORTIONAL COUNTER PROPORTIONAL COUNTER A proportional counter is a detector that operates in the proportional region. EO 2.1 DESCRIBE the operation of a proportional counter to include: a. Radiation detection b. Quenching c. Voltage variations A proportional counter is a Figure 7 Proportional Counter 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 to cause secondary ionizations (gas amplification) and increase the charge collected. These secondary ionizations may cause further ionization. In this region, there is a linear relationship between the number of ion pairs collected and applied voltage. A charge amplification of 10⁴ can be obtained in the proportional region. By proper functional arrangements, modifications, and biasing, the proportional counter can be used to detect alpha, beta, gamma, or neutron radiation in mixed radiation fields. To a limited degree, the fill-gas will determine what type of radiation the proportional counter will be able to detect. Argon and helium are the most frequently used fill gases and allow for the detection of alpha, beta, and gamma radiation. When detection of neutrons is necessary, the detectors are usually filled with boron-triflouride gas. The simplified circuit, illustrated in Figure 7, shows that the detector wall acts as one electrode, while the other electrode is a fine wire in the center of the chamber with a positive voltage applied. Rev. 0 Page 19 IC-06