Using NAI detectors for tomographic gamma scanning

The authors examined two approaches for using NaI detectors to perform transmission corrections used in the tomographic gamma scanner (TGS) and segmented gamma scanner (SGS) nondestructive assay methods. They found that a material-basis-set (MBS) fit using empirical logarithmic response spectra is quite accurate. Because this is a gross count technique, it gives sensitivities (for equal numbers of detectors) that are roughly ten times better than those obtained using Germanium detectors. The authors also found that simple continuum subtraction can be used in MBS fits using the energy-group-analysis technique only when the Pu transmission is greater than 10%. Both approaches for using NaI detectors require a knowledge of the Pu (or other) isotopics to obtain full accuracy

A demonstration of the gross count tomographic gamma scanner (GC-TGS) method for the nondestructive assay of transuranic waste

The authors examined the accuracy and sensitivity levels for three variations on the TGS method: the original TGS method using a high-purity germanium (HPGe) detector to measure net areas of full-energy gamma-ray peaks; a modified HPGe-detector method that uses net areas for the transmission analysis and the gross count TGS (GC-TGS) method for the emission analysis; and a NaI-detector method that uses the GC-TGS method exclusively. They found that while the accuracies of the methods were comparable, the GC-TGS method boosted the sensitivity per detector by a factor of approximately two for the HPGe GC variation and four for the NaI method. The implications for improved TGS scanner design are discussed

Characterization of mercury forms in contaminated floodplain soils

The chemical form or speciation of Hg in the floodplain soils of the East Fork Poplar Creek in Oak Ridge TN, a site contaminated from past industrial activity, was investigated. Hg speciation in the soils is an important factor in controlling the fate and effect of mercury at the site and in assessing human health and ecological risk. Application of 3 different sequential extraction speciation schemes indicated the Hg at the site was predominantly relatively insoluble mercuric sulfide or metallic Hg, though the relative proportions of each did not agree well between procedures. Application of x-ray and electron beam studies to site soils confirmed the presence of metacinnabar, a form of mercuric sulfide, the first known evidence of authigenic mercuric sulfide formation in soils

Cohort Profile: Pregnancy And Childhood Epigenetics (PACE) Consortium.

Development Psychopathology in context: famil

Methods of Reducing Bias in Combined Thermal/Epithermal Neutron (CTEN) Assays of Heterogeneous Waste

We examined the effectiveness of two different methods for correcting CTEN passive and active assays for bias due to variations in the source position in different drum types. Both use the same drum-averaged correction determined from a neural network trained to active flux monitor ratios as a starting point. One method then uses a neural network to obtain a spatial correction factor sensitive to the source location. The other method uses emission tomography. Both methods were found to give significantly improved assay accuracy over the drum-averaged correction, although more study is needed to determine which method works better

Evaluation of thermoplastic polyester molding resins. [Valox 420; Celanex 3300; Tenite 6H91; LNP WF-1006]

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