Experimental Technique of Measurement of Microscopic Energy Distribution in Irradiated Matter Using Rossi Counters

An experimental method for measuring the distribution of energies deposited in small tissue-equivalent volumes is described. The energy deposited in a cavity is measured by means of a proportional counter. The counter geometry and the associated electronics as well as properties of tissue-equivalent gases are discussed in detail. A calibration technique using soft x-rays generated by a miniature x-ray tube is described. Several relations are derived which help to determine limits of an experimental arrangement in terms of simulated tissue volumes. Examples of distribution of energies deposited by 60 Co gamma rays in tissue spheres of 0.5, 1, and 2 μm in diameter are given.