X-rays from an electron linear accelerator are pulsatory with the same pulse width and repeti-tion rate as those of the accelerator. Hence, from such X-rays, very high dose rate per pulse duration is obtained even when the average dose rate is low.
The counting loss in dose-rating with a pulse detector such as GM counter is discussed, and the relation of counting loss to average dose rate is clarified.
Example: When a GM counter of effective cross-sectional area of 20cm² is used for pulsed X-rays of maximum 18 MeV and repetition rate of 200 pps, the average dose rate with probable counting loss of 10% will be about 0.9mr/hr.
The relation of counting rate to pile-up of pulses in measuring pulsed X-ray spectrum is also discussed and a formula is derived for calculating the ratio of the number of signal pulses with no pile-up to that of total signal pulses.
Example: When the counting rate is below 1/5 of repetition rate of the electron beam, the ratio becomes 0.9 or more, in other words, over 90% of signal pulses are of correct height.