Spectrometry of a60Co Gamma-Ray Beam Used for Instrument Calibration

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Abstract
Measurements were made of the spectrum of one of the collimated 60Co gamma-ray beams employed in the instrument-calibration program of the National Bureau of Standards. The high-activity calibration-source capsule was replaced by one of low activity and identical geometry. The contributions to the spectrum by the scatter from the low-activity replacement source, the housing, and the collimation system were isolated by means of supplementary measurements in free air carried out on the replacement source and on a scatter-free source. Depending on collimator setting, the scatter contribution below 1 MeV was found to be between 13 and 19 percent of the total number of photons in the beam. A description is given of the measurements and of the technique for data reduction. Detailed spectral results are presented.