High dose rate effects observed in pulsed radiation dosimetry

Most important characters of pulsed radiation are its short pulse width and high dose rate. Short pulses are useable for the research of transient phenomena, and high dose rate is used for the researches of nuclear fusion, transient phenomena, etc. Usually, short pulse width is necessary to produce high doses with accelerators. The typical dosimeters used to measure high dose X-ray or electron beam are calorimeters, ionization chambers, film dosimeters and thermo luminescent detectors. High dose rate effects are found in the latter three types of dosimeters. A few examples are shown; the saturation effect appeared in the measurement of X-ray from a linac with a Radocon probe of type 607, and the dose rate effect was observed with four types of ionization chambers for four types of radiation, in which the total dose was set at 50 mR in every case, but the dose rate was varied from 50 mR/sec to 1000 mR/sec. The effect of oxygen on blue cellophane dosimetry under high pulsed dose, and high dose rate effects in mylar films and LiF TLD were observed. According to the survey of dose rate effect on TLD, the effect depends much on the material. Nowadays, it is considered that the dose rate effect is a new research field. (Wakatsuki, Y.)