The characterisation of an intertidal sediment from the Cumbrian coastline

The characterisation of an intertidal sediment, containing enhanced levels of radioactivity, collected from the Cumbrian coast of the U.K. by the Laboratory of the Government Chemist for the Department of the Environment is described. A wide variety of radiochemical and instrumental techniques were used including cr-spectrometry, P-counting, liquid scintillation counting, gamma-spectrometry, X-ray spectrometry and mass spectrometry. To derive mean values of the activity concentrations of radionuclides in the material, use was made of the technique developed by Woods and Munster. This technique first critically evaluates data for technical suitability. Then, to avoid excessive manipulation of data, calculation of the weighted (the statistical weighting is the inverse of the squared uncertainties, limited so that no one result contributes more than 50%) and unweighted means is performed, along with a chi(2) test. If the value of chi(2)/(n - 1) < 2, the weighted mean is accepted, otherwise a choice was made between the weighted or unweighted mean. This is done by considering if the uncertainties of both means overlapped, in which case the weighted mean was accepted and the unweighted mean if not. This enabled the derivation of a mean value, even if the data appeared to be inconsistent. In this paper, the history of the material is reviewed and the data analysis technique delineated. Data are presented for the activity concentrations of 21 radionuclides, with >2 determinations, 3 with 2 determinations and 2 with single determinations. Emphasis is placed where data appeared to be discrepant (e.g. K-40 and Cs-137), where widely different measurement techniques were employed (e.g. the actinides), where there were analytical "difficulties" (e.g. uranium) or where the radionuclide is not commonly measured (e.g. Eu-155,Np- 237 and Pu-241). The material is now available to laboratories as a reference material and it is anticipated that it will be used to validate existing procedures and to research new methods of analysis. (C) 1998 The National Physical Laboratory. Published by Elsevier Science Ltd. All rights reserved.