Dose rates from a cobalt-60 pool irradiator measured with Fricke dosimeters

This project used Fricke dosimeters to determine the dose rates at multiple locations in a Co pool irradiator. Fricke dosimetry is widely accepted as a chemical dosimetry method to measure radiation absorbed dose due to its simple recipe, linear response, wide dose range, good reproducibility, ease of measurements, and low operational cost. Calibration measurements were used to determine a molar extinction coefficient of 2,185 +/- 14 L mol cm at 303 nm and 25 degrees C; the molar extinction coefficient is comparable to values from the published literature. The Fricke dosimeters measured the dose rate of a National Institute of Standards and Technology-traceable calibrated gamma radiation field to within 1.2% of the calibrated value. The pool irradiator had the largest dose rates near the middle of the torpedo, with dose rate decreasing as one moved towards the bottom or top of the torpedo. The dose rate across the torpedo is not uniform at each level, because of the non-uniform distribution of source activity around the irradiator. Relative error in the Fricke dosimeter dose rate measurements ranged from 1-2%. The dose rates mapped in this project can be used to plan bulk sample irradiation, although dosimetry measurements should still be obtained to confirm delivered dose.