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A comparison of procedures used at UK nuclear sites for gamma assays of potentially contaminated or activated materials.

Dean, J C J (2007) A comparison of procedures used at UK nuclear sites for gamma assays of potentially contaminated or activated materials. NPL Report. IR 2

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Abstract

The National Physical Laboratory (NPL) has run a comparison exercise in which a single 200 L drum (containing a ‘soft-waste’ simulant spiked with a low-activity mixture of 241Am, 137Cs and 60Co, all traceable to national standards of radioactivity) was circulated to 18 groups on 16 UK nuclear sites for non-destructive assay. The exercise was followed by a workshop for discussion of the results, after which some participants submitted supplementary or replacement data and other information. This report summarises the background to the exercise, how the drum was prepared and standardised, the conduct of the exercise, the data analysis methods used at NPL, the outcomes of the workshop and the final results obtained. All submitted data (including any original data later revised by the participants) are tabulated, and the reasons for any changes are given. Of the final 88 results submitted, 51 agreed with the NPL values. Twenty-four of the remaining 37 results were either explained by the participants concerned or had been revised by the participants to provide supplementary values, but there were still 13 results which were either clearly discrepant or questionable. The exercise highlighted differences between laboratories who had used ‘ISOCS’ to model their sample detection efficiencies and facilitated an exchange of models between these laboratories. The exercise underlined the importance of a good knowledge of a sample in the modelling of detection efficiencies. A wide range of uncertainties was quoted, suggesting a need for guidance in the compilation of budgets. Some participants quoted MDA values for one or more radionuclides and some of these were below the activity concentration actually present. A second comparison, based on a sample with a heterogeneous activity distribution, is planned.

Item Type: Report/Guide (NPL Report)
NPL Report No.: IR 2
Subjects: Ionising Radiation
Ionising Radiation > Radioactivity
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4026

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