A comparison of some aqueous chemical dosimeters for absorbed doses of less than 1000 rads

Abstract

Several aqueous dosimeter solutions that have been used for the measurement of absorbed doses of less than 1000 rads were compared under identical irradiation conditions. The solutions used were: 1. (1) 2 × 10 −3 M ferrous sulphate/0.4 M sulphuric acid 2. (2) 1 × 10 −3 M benzoic acid 3. (3) 1 × 10 −4 M terephthalic acid/4 × 10 −4 M sodium hydroxide 4. (4) 1 × 10 −4 M ferrous sulphate/2 × 10 −4 M xylenol orange/5 × 10 −3 M benzoic acid/0.025 M sulphuric acid (FBX dosimeter). Particular attention was paid to spontaneous changes in solutions before and after irradiation. Small errors in the absorbance measurement of the unirradiated solution caused large errors in dose estimated from (1) for doses less than about 300 rads; however, careful calibration gave precision of better than 2% for all doses above 100 rads. Solution (2) is not as sensitive as (3) and suffers from post-irradiation changes. Solutions (3) and (4) can be used to measure doses as low as 4 rads, but both need to be calibrated using radiation sources of known dose rate. The measurement of fluorescence in solution (3) is not as convenient as absorbance measurement, but excellent linearity with dose was obtained from 3 to 800 rads with a precision of about 5% in the dose range 3–100 rads. The response of solution (4) to dose is not linear; corrections have to be made for changes in absorbance with time in both unirradiated and irradiated solutions.