A Single Ion Detector for Measurement of &b.Upsi;-ray Ionization in Cavities

Abstract

A new method of measuring the energy absorbed in a medium due to gamma-ray irradiation is described. The method requires that a counting device have linear dimensions which are small compared to the mean free path for ionization of the counting gas by the secondary electrons. Under this condition the number of ionizing events in the counter is proportional to the energy absorbed in the gas; thus the energy absorbed in the surrounding wall may be inferred from the count rate by means of the Bragg-Gray principle. Application of the method is made to a tissue dosimeter which is capable of measuring the dose due to gamma-rays even when mixed with fast neutrons.