H-1 NMR and optical spectroscopy study of the radiodosimetric properties of the PIRA gel

The radiation-response of the Fricke-doped protein-polymer gel (PIRA) was s tudied by H-1 NMR, as well as with spectrophotometric and fluorescence meth ods. In this gel, the ionizing radiation induces an increase in the NMR lon gitudinal relaxation rate, R1, of protons. It was observed that: I) the mai n mechanism responsible for the increase in R1 was the oxidation of ferrous to ferric ions; ii) the total amount of acrylamide with the same weight fr action (50%C) of the crosslinker N,N'-methylene-bis-acrylamide in the range 6%-12% by weight had no effect upon the R1 dose sensitivity; iii) the incr ease in the bovine serum albumin (BSA) concentration caused a drop in the R 1 dose response sensitivity; iv) the R1 dose sensitivity was pH dependent. The four-site fast exchange model for R1 dose response was applied to calcu late the ferric ions chemical yield G(Fe3+). The G(Fe3+) value obtained fro m the NMR data agreed with that determined independently from spectrophotom etric measurements.