Compton Dosimeter for Measurement of Penetrating X-Rays and Gamma Rays

Professor John Trump in 1957 called the attention of the author to the fact that the y-radiation from extremely strong sources can, even in the absence of an applied field, produce electrical breakdown of insulators. This effect, caused by the secondary Compton electrons produced by the y-rays, demonstrates the intensity of the electron irradiation and space-charge effects associated with the absorption of high-intensity high-energy photon beams. Less conspicuous, but equally interesting, are currents which the high-energy radiation produces in the dielectric and wall material of ionization chambers and which, under certain conditions, produce a polarity effect that can amount to 50 % of the ionization current (1-3). Johns et al. (4) have discussed this effect in detail and reported a series of measurements. Similar currents were observed in the course of measurements of radiation-induced conductivity by Meyer et al. (5). These authors have pointed out that the Compton electrons are scattered preferentially in the forward direction; therefore a unidirectional beam of photons in an insulator can produce a directional current in the absence of an electric field. They found that in some instances this Compton electron current exceeded the conduction currents produced by irradiation in an applied electric field. The present author has observed charge storage and electrostatic effects in borosilicate glass after y-irradiation (6); these effects probably were due to the Compton electron flux. The intensity of the Compton current is proportional to the radiation dose rate. Therefore radiation dosimeters can be built which are based on the measurements of this current. They are extremely simple and very rugged, can operate with high radiation doses, have a fast response, and do not need any auxiliary voltage. They are batteryless electrical radiation receivers. A preliminary discussion of this subject has been given in an earlier paper (7).