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Introduction Reference materials of known properties are commonly used to calibrate, verify, or validate the performance of test instruments or methods. In dynamic mechanical analysis, spring steel is commonly used to calibrate

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Instrumental neutron activation analysis, atomic absorption spectrometry and conventional methods were used on five USGS Geochemical Exploration Reference Materials: GXR-1, 2, 3, 4 and 6. The concentrations of 35 elements are reported and compared with available literature values. In general the agreement is good.

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The concentration levels of total iodine obtained by RNAA in different sorts of tobacco, including the reference sample Kentucky Tobacco 2RI, two new candidate reference materials, Oriental Tobacco Leaves /CTA-OTL-1/ and Virginia Tobacco Leaves /CTA-VTL-2/ prepared in the Institute of Nuclear Chemistry and Technology, Warsaw, and some biological SRMs, are presented and discussed.

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The IAEA laboratories have access to both nuclear analytical methods and conventional instrumental methods for trace analysis for the characterisation of its environmental and biological reference materials. A technical concept integrating the homogeneity data, the recommended test portion mass and the uncertainty on the trace element concentrations is explored using a combination of INAA, XRF, ICP-MS, ICP-AES, and AAS. The above approach is illustrated by selected examples of reference materials currently under evaluation for their trace element content. They include some or all of the following elements Al, As, Br, Ca, Cd, Co, Cr, Cs, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, Rb, Se, Sr, Th, U, Zn in environmental biomonitor organisms (lichen, algae) and air dust filters.

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Two fairly recent sediment reference materials (MESS-1, PACS-1) have been analyzed by INAA in order to determine the concentration of their elements and to ascertain the homogeneity of each standard. Two rock samples (USGS-GSP-1 and JG-1) were used as standards for the determination of element concentrations, for inter-calibration purposes and also to assess the precision of the technique used. Eighteen elements were determined in these sediments. Comparison of the certified values with our results, where this is possible, indicates the accuracy of the method for environmental studies. These materials were shown to be very homogeneous and hence useful as sediment standards. The data presented here extend the range of useful element concentrations in these reference materials.

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A number of reference materials for oxygen in different non-ferrous metals have been certified by BCR in the frame of a multidisciplinary Community project. The contribution of nuclear analysis methods is illustrated by several examples concerning the optimization of sample preparation techniques, the analysis of low and high oxygen non-ferrous metals and the extension of the program to other non-metals, especially nitrogen and carbon.

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Instrumental neutron activation analysis (INAA) has been applied to the determination of 21 elements in 8 different vegetal samples, to be used as reference materials in 35 European laboratories (CII). Many of these elements hitherto have not been evaluated; they can be useful markers in many environmental problems. The INAA values are compared with CII non-nuclear analytical techniques results. Some rare earths elements (REE) have been also determined and their chondritic ratio versus atomic radius is reported.

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The Standard Reference Material 4351 from the National Institute of Standards and Technology is acknowledged to be inhomogeneous. The value of a single analysis for239Pu+240Pu could lie within a wide range, but the accuracy of the analysis can be corroborated by comparing the corresponding238Pu/239Pu+240Pu or240Pu/239Pu values with the relationships between these ratios and the total plutonium concentration.

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Instrumental NAA based on short-lived radionuclides implies high initial total count rates which change appreciably over the counting period. This in turn necessitates corrections for three negative biases: losses due to differences in counting time between samples and standards; pile-up losses, and (residual) influence of dead-time. The procedure is demonstrated for the determination of Al, Ca, V and Mn in the IAEA Reference Material 395 Urban Dust. The obtained data are in good agreement with the reference values for this material. By limiting the total relative dead-time to 25%, statistical uncertainties are below 5%.

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