The many manifestations of successful partnership

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Methods for analysis of trace elements in coal, coal fly ash, soil, and plant samples. [59 refs]

Results of a literature search are presented, and analytical methods are proposed for studies of trace elements in coal, coal ash residue, soil, and vegetation. Increased trace element levels in soils and plants collected near power plants have been reported by several investigators. Many sample dissolution and analysis techniques were used in the reported studies. A nine-laboratory comparison of trace element analyses for a variety of methods showed excessive variation relative to quoted uncertainty limits. Analysis results from a subsequent four-laboratory comparison of instrumental nuclear techniques for trace element analysis agreed with the National Bureau of Standards certified values for all nine elements determined. Instrumental neutron activation analysis, spark source mass spectrometry, and atomic absorption spectrometry are proposed as primary analysis methods for coal, coal ash, soil, and plants in a Savannah River Laboratory study of trace elements. Bomb procedures are proposed for dissolution of samples

Measurement of reactor tube cladding thickness by x-ray fluorescence spectrometry

An x-ray fluorescence spectrometer was designed and fabricated which nondestructively determines the thickness of aluminum cladding at small suspected thin spots in the inner or outer surface of actinide reactor tubes. The analysis method is based on the difference in absorption of actinide L/sub ..cap alpha../ and L/sub ..beta../ fluorescent x-rays in passing through the cladding. Calibration plots of the logarithm of the L/sub ..beta..//L/sub ..cap alpha../ x-ray intensity ratio versus cladding thickness are linear to at least 40 mils for U-Al, U/sub 3/O/sub 8/-Al, and PuO/sub 2/-Al substrates. Accuracy and precision of the experimentally determined cladding thickness and evaluated for both uranium and plutonium substrates. Experimental thickness data are reported for 618 quality assurance analyses on six Mark 41 PuO/sub 2/-Al target tubes. An x-ray fluorescence cladding thickness monitor operated with a computer-controlled fluoroscope holds considerable promise for quality assurance because (1) a permanent record of cladding thickness for each reactor tube would be provided and (2) the cladding integrity of each tube would be assured before irradiation in the reactor

Use of an analytical model for optimizing the design of a small-animal PET scanner with DOI capability - Size 7.4E-02 m Size 1.14E-01 m

The optimization of spatial resolution is a critical issue for small-animal PET scanners, and is often addressed by Monte-Carlo simulation. Analytical models, though less versatile are very fast and their simplicity allows a direct appreciation of the influence of different model parameters. The authors have developed an analytical model for multi-layer PET systems, which provides estimates of the radial and tangential resolution at different positions within the field of view. After a preliminary validation, this model was used to optimize the design of a small single-slice multi-layer PET scanner with depth of interaction capability. The authors found satisfactory agreement between the analytical model and Monte Carlo results for several scanner configurations. The dependence of the resolution on the crystal width, the number of layers, and the crystal layout was determined for a scanner with internal and external diameters at 74 mm and 114 mm respectively. Both simulation methods agreed perfectly on the influence of these parameters. In particular confirming the degree of resolution improvement obtained using multiple-layers of crystals. These results show that an analytical model can provide accurate estimates of the spatial resolution, and can be used to complement or cross-validate Monte Carlo simulations. (7 References)

An improved analytical detector response function model for multilayer small-diameter PET scanners

The optimization of spatial resolution is a critical consideration in the design of small-diameter positron emission tomography (PET) scanners for animal imaging, and is often addressed with Monte Carlo simulations. As a faster and simpler solution, we have developed a new analytical model of the PET detector response function, and implemented the model for a small single-slice, multilayer PET scanner. The accuracy of the model has been assessed by comparison with both Monte Carlo simulations and experimental measurements published in the literature. Results from the analytical model agreed well with the Monte Carlo method, being noise free and two to three orders of magnitude faster. The only major discrepancy was a slight underestimation of the width of the point spread function by the analytical method as inter-crystal scatter is neglected. We observed good agreement between the predictions of the model and experimental measurements. For two large-diameter scanners additional discrepancies were seen due to photon acollinearity, which is not considered in the model. We have shown that the simple and fast analytical detector response function model can provide accurate estimates of spatial resolution for small-diameter PET scanners, and could be a useful tool for several applications, complementing or cross-validating other simulation methods