Proportional Counter Circuitry

Radiation Detectors PROPORTIONAL COUNTER CIRCUITRY Figure 11 Single Channel Analyzer Output Since the single channel analyzer can be set so that an output is only produced by a certain pulse size, it provides for the counting of one specific radiation in a mixed radiation field. This output is fed to a scaler which counts the number of pulses it receives. A timer gates the scaler so that the scaler counts the pulses for a predetermined length of time. Knowing the number of counts per a given time interval allows calculation of the count rate (number of counts per unit time). Proportional counters can also count neutrons by introducing boron into the chamber. The most common means of introducing boron is by combining it with tri-fluoride gas to form Boron Tri-Fluoride (BF₃). When a neutron interacts with a boron atom, an alpha particle is emitted. The BF₃ counter can be made sensitive to neutrons and not to gamma rays. Gamma rays can be eliminated because the neutron-induced alpha particles produce more ionizations than gamma rays produce. This is due mainly to the fact that gamma ray-induced electrons have a much longer range than the dimensions of the chamber; the alpha particle energy is, in most cases, greater than gamma rays produced in a reactor. Therefore, neutron pulses are much larger than gamma ray-produced pulses. Rev. 0 Page 25 IC-06