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

Abstract

Addition of iron(III) sulfate (Fe₂(SO₄)₃) to the methyl viologen (MV²⁺)-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 MV²⁺-PVA film (<14 kGy). In the MV²⁺-Fe₂(SO₄)₃-PVA film, iron(II) ion (Fe²⁺) was also accumulated without any induction dose. The Fe²⁺ 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 Fe³⁺ ((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 MV²⁺ and Fe³⁺, and the resulting MV^+. successively reacts with neighboring Fe³⁺ to regenerate MV²⁺ in the initial stage of irradiation (within D_i). At the dose of D_i, such neighboring Fe³⁺ is consumed entirely and substantial formation of MV^+. can be observed.