Measurement of neutrons from an electron accelerator by rem-counter

Abstract

In the measurement of neutrons from the medical electron accelerator by a rem counter, two problems disturb accurate measurements. One is the pile-up of signals produced by X-rays during each X-ray burst and the other is the increased counting loss caused by bunched nature of yielded neutrons. The time spectrum of neutrons measured by the rem counter 2202 D (manufactured by Studsvik) rises up to a maximum value by about 20 microseconds and then falls down exponentially with a time constant of about 90 microseconds. On the other hand, that of X-rays is roughly rectangular with several microseconds width. A time discriminating system was prepared to be combined with the rem counter, which was triggered by leading edge of electron beam pulses, rejected pile-up signals due to X-ray bursts, and counted pulses of neutrons in a specified time window. The system discriminated the pile-up enough to measure neutrons at a X-ray dose rate of at least 30 mGy/h. Nonparalyzable counting loss correction was practicable upto about 10 mSv/h for the beam pulse rate of 85 Hz, in which the dead time of the rem counter was estimated as 4 microseconds.