Valine-spectrophotometric readout dosimeter (1Â Gy-50Â kGy)

In this method 20 mg unirradiated/irradiated L-valine powder [(CH3)2CH·NH2CH·COOH] is dissolved in 10 ml of a solution containing 4×10−4 mol dm−3 Fe2+ and 2.5×10−4 mol dm−3 xylenol orange (XO) in aerated aqueous 0.060 mol dm−3 sulphuric acid (FX). The plot of absorbance at 550 nm against dose is non linear. A dose of 1-50 kGy can be measured. However, dosimeter can be sensitized in the dose range of 1 to 16 kGy by dissolving 50-mg valine powder in 10 ml of a solution which contains 5×10−4 mol dm−3 Fe2+ and 3×10−4 mol dm−3 XO in aerated aqueous 0.065 mol dm−3 sulphuric acid. The plot of absorbance at 549 nm against dose is non-linear. However, dosimeter shows linear response when 500 mg unirradiated/irradiated L-valine powder is dissolved in 10 ml of a solution containing 7.5×10−4 mol dm−3 Fe2+ and 3×10−4 mol dm−3 XO in aerated aqueous 0.25 mol dm−3 sulphuric acid. The plot of absorbance at 557 nm against dose is linear in the dose range of 20-400Gy and doses down to about 1  Gy can be measured using 10-cm path cells. Response of the dosimeter is independent of irradiation temperature in the temperature range 20-50 °C. Irradiated valine powder is stable for about 1 month. The reproducibility of the method is better than ±2%. This dosimeter is very useful as transfer dosimeter for food irradiation and radiation sterilization.