Frederick V. Sloop

Organic scintillators for neutron detection

The goal of the present work has been to develop a method for the efficient and reliable production of gadolinium- and boron-containing solid scintillator. Polyvinyl toluene, silicone rubber, and other materials were investigated. Gadolinium in a solid overcomes the limitations of the physical form of a liquid, and silicone rubber as a carrier for either gadolinium or boron overcomes the thermal limitations of plastics. Silicone rubbers also introduce some interesting and useful properties (such as flexibility) of their own. We report here the fabrication of solid organic scintillators loaded with as much as 2% gadolinium, and more than 5% boron. A gadolinium-containing compound, soluble in vinyl toluene monomer and not inhibiting polymerization, was found. The same compound was also found to be soluble in phenyl-substituted silicone fluids that subsequently could be polymerized. In addition, a class of boron compounds also soluble in silicone fluids and not inhibiting polymerization was found. In the absence of phosphors, the resulting boron- and gadolinium-loaded disks were clear and colorless, or only slightly yellow. The disks were compatible with UV-, blue-, blue-green, and green-emitting phosphors and a variety of colors were realized. In addition, it was found in the case of gadolinium loading, the discrete spectrum due to atomic x-rays and conversion was observable if the scintillator sample was small.

Biological Markers in Animal Sentinels: Laboratory Studies Improve Interpretation of Field Data

A number of approaches have been used to evaluate the biological hazards of environmental pollution. Chemical analysis of the concentrations of toxic compounds in environmental media is clearly an important component of such an evaluation. Advanced analytical procedures are specific, quantitative, and exquisitely sensitive and precise. However, the biological significance of the chemical concentrations is not at all clear. We understand the toxic action of but a few of the thousands of chemicals in the environment and have almost no information on the toxicity of complex mixtures of chemicals. Furthermore, a chemical survey is a snapshot in time and space. Variations in concentrations over time resulting from intermittent releases of effluents by industries or from storm events, changes in winds, etc., cannot be accounted for without repeated analyses. Spatial patchiness of contaminant patterns also requires extensive and expensive sampling and chemical analyses.

Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants

This report presents the work that followed the CSSX model development completed in FY2002. The developed cesium and potassium extraction model was based on extraction data obtained from simple aqueous media. It was tested to ensure the validity of the prediction for the cesium extraction from actual waste. Compositions of the actual tank waste were obtained from the Savannah River Site personnel and were used to prepare defined simulants and to predict cesium distribution ratios using the model. It was therefore possible to compare the cesium distribution ratios obtained from the actual waste, the simulant, and the predicted values. It was determined that the predicted values agree with the measured values for the simulants. Predicted values also agreed, with three exceptions, with measured values for the tank wastes. Discrepancies were attributed in part to the uncertainty in the cation/anion balance in the actual waste composition, but likely more so to the uncertainty in the potassium concentration in the waste, given the demonstrated large competing effect of this metal on cesium extraction. It was demonstrated that the upper limit for the potassium concentration in the feed ought to not exceed 0.05 M in order to maintain suitable cesium distribution ratios.

Resonance ionization spectroscopy for multiplex sequencing of tin-labeled DNA.

A method is described for synthesis of a tin reagent, triethylstannylpropanoic acid (TESPA), and its attachment to oligonucleotide primers. Except for the expected mobility retardation, the presence of [116Sn]-TESPA did not affect the sequencing ladder on electrophoresis gels. By using [120Sn]-TESPA and [35S]-dTTP simultaneously in the Sanger procedure, DNA bands on an electrophoresis gel were first located by autoradiography and then by resonance ionization spectroscopy to demonstrate the coincidence of the signals. Previous results using stable isotopes as labels on model compounds are now confirmed by their use in actual DNA sequencing products.

Bis-lactam-1,10-phenanthroline (BLPhen), a New Type of Preorganized Mixed N,O-Donor Ligand That Separates Am(III) over Eu(III) with Exceptionally High Efficiency

We report a new family of preorganized bis-lactam-1,10-phenanthroline (BLPhen) complexants that possess both hard and soft donor atoms within a convergent cavity and show unprecedented extraction strength for the trivalent f-block metal ions. BLPhen ligands with saturated and unsaturated δ-lactam rings have notable differences in their affinity and selectivity for Am(III) over Eu(III), with the latter being the most selective mixed N,O-donor extractant of Am(III) reported to date. Saturated BLPhen was crystallized with five Ln(III) nitrates to form charge-neutral 1:1 complexes in the solid state. DFT calculations further elaborate on the variety of effects that dictate the performance of these preorganized compounds.