EXPOSURE-RATE CALIBRATION OF SMALL RADIOACTIVE SOURCES OF CO-60, RA-226 AND CS-7

A comparison between measurements made at the National Physical Laboratory (NPL) and at The Radiochemical Center Ltd (TRCL) has been carried out in order to assess the accuracy of TRCL's exposure rate calibrations for sources of gamma radiation of a few tens of mCi activity. TRCL calibrations are based either on measurement of absolute disintegration rates together with a knowledge of exposure-rate constants, or, for clinical sources, on a comparison with a secondary standard radium source. The exposure rates measured by NPL were about 3% higher than those stated by TRCL. A similar discrepancy was found between the measured and calculated values for the NPL radium source. These discrepancies are within the arithmetic sum of the estimated uncertainities of the measurements.