BF₃ Proportional Counter Circuit:

Figure: BF₃ Proportional Counter Circuit

The BF₃ proportional counter is used to monitor low power stages in a nuclear reactor.  BF₃ proportional counter circuit is used in the "startup" or "source range" channels.  The Proportional counters cannot be used at high power levels since they are pulse-type detectors.  Classically, it takes 10 to 20 microseconds for every pulse to go from 10% of its peak, to its peak, and back to 10 percent.  The two pulses are superimposed if another neutron interacts in the chamber during this time. The voltage outcome would never drop to zero among the two pulses, and the chamber would draw a steady current as electrons are being generates.