Proficiency test data interpretation and data rejection.

An extension to the interpretation, evaluation and visualisation of radioactivity proficiency test exercises (PTEs) are presented in this paper. In addition to the use of the ζ- and z-tests, a test for acceptance of relative uncertainties is introduced, the R-test, along with an overall performance score and additional data visualisation using modified Naji- and Pom-plots. Additionally, 'improbable deviations' are identified using a simple test. Other outliers may be identified in the remaining data using Peirce's Criterion.

Development of synthetic environmental radioactivity reference materials.

In this paper, a novel way of developing synthetic environmental radioactivity reference materials via the sol-gel process is described. Two solid reference materials (both having a SiO(2) matrix) were synthesised by hydrolysing a liquid mixture of tetraethyl orthosilicate (TEOS), ethanol and standardised mixed radionuclide solutions. The certified values, which were in the Bqg(-1) range, for the radionuclides in the material were determined by NPL and compared with results from measurements made by 36 organisations from 17 countries using a 'consensus' approach. The measurements were made within two wider test exercises (the NPL Environmental Radioactivity Proficiency Test Exercises 2009 and 2010). Certified activity concentration values were obtained for (60)Co, (133)Ba, (134)Cs, (137)Cs, (152)Eu, (154)Eu and (241)Am and indicative values were obtained for (55)Fe and (90)Sr.

Determination of carbon-14 in environmental level, solid reference materials.

An intercomparison exercise to determine the (14)C activity concentrations in a range of solid, environmental level materials was conducted between laboratories in the UK. IAEA reference materials, C2, C6 and C7, and an in-house laboratory QA material were dispatched in 2006 to ten laboratories comprising of members of the Analyst Informal Working Group (AIWG) and one other invited party. The laboratories performed the determinations using a number of techniques, and using the results each one was evaluated in terms of levels of precision, sensitivity and limits of detection. The results of the study show that all techniques are capable of successfully analysing (14)C in environmental level materials, however, a shortage of certified environmental reference materials exists. The suitability of the IAEA reference materials and other material for use as reference materials was also assessed.

Development of a neutron-activated concrete powder reference material.

In this paper, the development of a neutron-activated concrete powder reference material is described. The material originated from core samples taken from a concrete bioshield of a decommissioned nuclear reactor which ceased operation almost 30 years ago after approximately 20 years of operation. The assigned values, which were in the Bq g(-1) range, for the radionuclides in the material were determined by a 'consensus' method from measurements made by 33 organisations from 15 countries. The measurements were made within a wider test exercise (the NPL Environmental Radioactivity Proficiency Test Exercise 2008). Assigned specific activity values were obtained for (60)Co, (133)Ba, (152)Eu and (154)Eu and indicative values were obtained for (3)H (total), (3)H (leachable), (14)C, (40)K, (55)Fe and (63)Ni.

Decay correction of 95Nb.

The (95)Nb/(95)Zr activity ratio can be used to determine the date of a nuclear event. Several proficiency test exercises organised by the National Physical Laboratory (NPL) showed in general relatively poor results for (95)Nb, presumably caused by incorrect decay corrections. In this paper, the integrated Bateman equation taking account of the multiple branching of the parents (95)Zr and (95m)Nb, ingrowth/decay during measurement and the decay correction to a specific reference time is presented.