Matrix materials for proficiency testing: optimization of a procedure for spiking soil with gamma-emitting radionuclides

On the equivalence between homogeneously prepared sources and sources prepared by seeding in layers for different geometries, energies and matrix parameters

Measuring the radioactive content of environmental samples requires the use of appropriate reference materials with the same composition and density as the matrices to be measured. If they are not available, ad hoc artificially spiked reference materials are an alternative. Spiking in layers requires a detailed study of the drop distribution, as energy and decay scheme of the component radionuclides must be taken into account to produce a reference material that represents, in efficiency terms, a real sample. A method based on Monte Carlo simulation has been developed to find the optimal distribution of drops in layers for the combination of two typical soil samples and four radionuclides. Results have been validated by comparison with samples prepared by two techniques: methanol bath and spiking in layers.

Spiked environmental matrix for use as a reference material for gamma-ray spectrometry: Production and homogeneity test

The application of a spiking method for reference material production and its utilisation for a food matrix is presented. The raw rice powder was tested by means of γ-ray spectrometry and spiked with a (137)Cs solution. The spiked material was mixed and tested for homogeneity. The future use of the rice powder reference material after the entire characterisation cycle will be for γ-ray spectrometry method validation.

Preparation of water samples for proficiency testing on radionuclides

The Institute of Nuclear Chemistry and Technology (INCT) procedure for preparation of water samples for proficiency testing on determination of (241)Am, (137)Cs, (239)Pu, (226)Ra and (90)Sr in water is presented. Natural waters were applied as the raw materials and spiked with the aforementioned radionuclides. The procedure of spiking water allows to prevent losses of the radionuclides and to assign property values from formulation. The main advantages of this procedure are (i) similarity of the test materials to the water samples routinely analysed by radioanalytical laboratories, and (ii) traceable assigned values with low uncertainties.

Preparation and characterisation of a (226)Ra spiked slag as reference material for radioactive control of steelworks

One of the issues of the European Research Project MetroMetal is to develop reference materials in order to provide SI-traceable radioactivity monitoring in foundries. For this purpose, a protocol for preparing a set of identical standard slag samples, containing known activity concentrations of (226)Ra, has been developed. This paper describes the preparation of the raw material, the characterisation in terms of its mineralogical, chemical and radiological features, the spiking procedure and the homogeneity testing of the spiked samples.

Preparation of spiked grass for use as an environmental radioactivity reference material

Measurement of radionuclides from environmental samples includes a wide variety of matrix compositions and densities. To improve the traceability of environmental monitoring, LNE-LNHB intends to produce mixed γ-ray reference materials with a known mass activity and a composition as representative as possible of real environmental samples. This paper describes the preparation and characterization of a low density treated grass matrix spiked with mixed γ-emitters. This material was used in a proficiency test exercise whose results are presented.

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.