New data concerning the efficiency calibration of a drum waste assay system. Part I: Experimental calibration

The study is focused on the efficiency calibration of the gamma spectroscopy system used in the NIPNE drum waste assay facility. The measurement of a radioactive drum waste is generally difficult because of its high volume, the complex and usually unknown distribution of the waste in the drum and its high self-attenuation. To solve these problems, a complex calibration of the system is required. For this purpose, a calibration drum filled with Portland cement and provided with seven tubes, placed at different distances from its center was used. For the efficiency calibration appropriate for a uniformly distributed source, the shell method, using a linear source of 152 Eu, was applied. The linear calibration source was introduced successively in the seven tubes, the gamma-spectra were collected while the drum was translated and simultaneously rotated. Using the GENIE-PC software, the gamma-spectra were analyzed and the detection efficiencies were obtained. For the efficiency calibration in the case of a non-homogenous source, supplemental measurements in the following geometries were made. First with a point source of 152 Eu placed in front of the detector, measured in all seven tubes, the drum being only rotated. Second with the linear source of 152 Eu placed in front of the detector, measured in all seven tubes, the drum being only rotated. For each case the gamma spectra were recorded and the detection efficiency was calculated. (authors)