Measurements on the Spectral Distribution of the Absorbed Dose Delivered by ⁶⁰Co Gamma Rays

Abstract

A method is presented which makes possible to measure directly the absorbed dose in soft tissue exposed to gamma rays and X-rays and in addition to clarify the dependence of the spectral distribution of absorbed dose on the size of tissue element. The term TEIT (transfered energy per individual track) is introduced and the absorbed dose is expressed in the form of the spectral distribution as a function of TEIT. A brief argument is given which indicates the relation between the spectral distribution in TEIT and that in LET. Actual measurements have been performed on the absorbed dose in soft tissue represented by plastic scintillators of various sizes exposed to ⁶⁰Co gamma rays using a scintillation spectrometer. From three types of measurements the followings have been derived: 1) the variation of the spectral distribution of dose in TEIT with the tissue size, 2) the variation of dose with depth, and 3) the structure of dose of dose close to the bone-tissue interface.