Radiation Intensity Measurements with Silver-Activated Glass Block Dosimeters

Abstract

The intensity of radiation at a given place may be defined in general as the energy per unit time entering a small sphere centered at that place per unit cross-sectional area of the sphere (1). In the special case of a unidirectional X-ray or electron beam, the intensity may be defined as the energy per unit time impinging upon a unit crosssectional area oriented at right angles to the direction of the radiation beam. The latter case is frequently encountered experimentally in the form of a plane-parallel X-ray or electron beam. The intensity (ergs/cm2-sec or ev/cm2-sec) at some point of interest may be measured by the total absorption of the radiation arriving there, the absorber being some material that changes in a measurable way as a known function of the energy absorbed per unit area. For example, one might totally absorb an X-ray beam in a calorimeter or large volume of ferrous sulfate solution. Such wellunderstood dosimeters are not always easily employed in many experiments where space is limited and the environment of the specimen under study precludes the use of such absolute dosimetry systems. One can avoid these difficulties by choosing as a dosimeter some material that is more compatible with the environmental conditions of the experiment. Glass that darkens under the influence of ionizing radiation is an example of such a material. This sort of dosimeter need not be absolute in itself, since it can be calibrated against one of the previously mentioned absolute dosimetersthat is, a calorimeter or the Fricke dosimeter. It has the important advantage of small physical size approximating that of many samples, so that it can be employed without alteration of the geometry of the experiment. Rabin and Klick (2) and Ritz (3) have used glass block dosimeters to measure the intensity of low-energy X-ray beams and to determine the fraction of the incident intensity absorbed by thin alkali halide crystals irradiated in a cryostat. These blocks (1 cm X 1 cm X 0.3 cm thick) are made of a silver-activated metaphosphate