Calibration of intense 60Co gamma ray sources at the Savannah River Plant

Three different dosimeters were used to calibrate Savannah River Plant 60Co sources having intensities greater than 107 rads/hr. These dosimeters are (a) ceric sulfate dissolved in 0.4M H2SO4, (b) oxalic acid dissolved in water, and (c) a commercially available nylon film containing a radiochromic dye. Response per unit dose to these dosimeters is independent of radiation intensity at 104 to 1011 rads/hr. The dosimeters were calibrated at 6.0 x 105 rads/hr with a 60Co source whose intensity was determined with the standard Fricke dosimeter. For the sources at 107 rads/hr or greater, intensities were calculated from slopes of linear plots of dosimeter response versus irradiation time. Individual dose rates varied from 1.0 x 107 to 4.6 x 107 rads/hr. Each source was calibrated with at least two different dosimeters. Relative standard deviations varied from 2 to 9 percent. A conservative estimate of the uncertainty in the accuracy of these dosimeters is 10 percent. Of the three dosimeters, the nylon film is easiest to use and is therefore recommended for future calibrations