Effect of iron(III) sulphate on radiation-induced reduction of methyl viologen incorporated in poly(vinyl alcohol) film

Abstract

Addition of iron(III) sulfate (Fe 2(SO 4) 3) to the methyl viologen (MV 2+)-poly(vinyl alcohol) (PVA) film dosimeter led to the induction dose ( D i) before appearance of blue-colored cation radical (MV +.) and reduction of G-value of MV +.. As a result, the measurable range for ionizing radiation (200 kV electron beam) was expanded to the higher dose >400 kGy, which was >25 times larger than that of base MV 2+-PVA film (<14 kGy). In the MV 2+-Fe 2(SO 4) 3-PVA film, iron(II) ion (Fe 2+) was also accumulated without any induction dose. The Fe 2+ still increased after D i, with the G-value relatively smaller than that before D i. Increase in pH ((pH) i) of the source aqueous PVA solution, subjected to casting into films, led to the decrease in D i and increase in G-value of MV +. ( G(MV +.)). The ratio of initial concentration of Fe 3+ (( C Fe) i) to D i was apparently independent of ( C Fe) i at given (pH) i. These results suggest the mechanism that radiation-induced electrons in the PVA matrix reduce both MV 2+ and Fe 3+, and the resulting MV +. successively reacts with neighboring Fe 3+ to regenerate MV 2+ in the initial stage of irradiation (within D i). At the dose of D i, such neighboring Fe 3+ is consumed entirely and substantial formation of MV +. can be observed.