Energy Dependence of Free Radical Production in Alanine

Abstract

It has been shown by Bradshaw et al. (1) that the amino acid dl-alanine in dry powdered form is a sensitive and accurate y-ray dosimeter. When it is exposed to directly and indirectly ionizing radiations, free radicals are formed and their relative concentration can be measured by electron spin resonance (ESR) spectrometry. The free radicals are stable, decaying only about 5% in 90 days (1). Evidence indicates that the free radical CH3-C--COOH is formed in alanine after exposure to ionizing radiation at room temperature (2, 3). In the work of Bradshaw et al., it was found that the ESR amplitude, which is proportional to the number of free radicals formed in the alanine sample, was proportional to the measured exposure dose and presumably to the absorbed dose. Rotblat and Simmons (4) have shown in electron experiments that in alanine the ESR amplitude saturates in the megarad dose region, indicating that this substance can be used over a wide range of doses. In an attempt to measure the characteristics of alanine as a neutron dosimeter and thereby add to the data presented in reference 1, results of irradiations with neutrons and low-energy X-rays that were not in agreement with those of Bradshaw et al. (1) indicated the necessity of more knowledge of the dependence of free radical production in amino acids on particle energy and mass (5, 6). This paper is a report of these measurements and of further experiments to measure the properties of alanine as an Xand y-ray dosimeter.