NBS (National Bureau of Standards) Measurement Services: Calibration of X-ray and Gamma-ray Measuring Instruments

摘要

The calibration and irradiation of x-ray and gamma-ray instruments are performed in terms of the physical quantity exposure. The calibrations are listed in NBS Special Publication 250 as calibrations 46010C through 46050S (formerly 8.3A through 8.3M). A calibration or correction factor is provided for radiation detectors, charge sensitivity of a high-gain electrometer is tested, and passive dosimeters are given known exposures. Calibration is performed by comparing the instrument against an NBS primary standard of exposure, which is a free-air chamber for x-rays and a cavity ionization chamber for cesium-137 and cobalt-60 gamma rays. A variety of quality assurance checks are performed to assure the constancy of the standards and the accuracy of the calibrations and irradiations. The overall uncertainty is given as 0.7% for exposure rate in the NBS beams, 1% for calibration of a cable-connected chamber and irradiation of passive dosimeters, and 1.5% for calibration of a condenser chamber.