A SPIN-SPIN RELAXATION RATE INVESTIGATION OF THE GELATIN FERROUS SULFATE NMR DOSIMETER

Spin-spin NMR relaxation rate in the ferrous sulphate gelatin dosimeter has been studied in terms of pH, gelatin concentration, the addition of benzoic acid, and sample size. It is demonstrated that R(2) is more sensitive to changes in Fe3+ ion concentration than R(1) when measuring at frequencies of 64 and 100 MHz. PH has an important effect on dose response curves, and oxygen depletion occurs significantly more rapidly in FeSO4 gelatin than in the liquid FeSO4, resulting in a saturation dose of similar to 80 Gy at depths greater than similar to 3 mm in phantom. The concentration of gelatin can be increased to 12% by weight, and the dosimeter will continue to exhibit a linear dose response. Sensitivity is maintained at higher gel concentrations by PH compensation. Addition of low-concentration benzoic acid to the system does not alter the dose response of the gelatin FeSO4 system. Finally, spontaneous oxidation of Fe2+ ions does not significantly alter the shape of dose response curves but does result in increases in R(2) by UP to 4% per day.