Establishing reactor operations from uranium targets used for the production of plutonium

This paper presents results from the examination of a number of archived neutron-irradiated uranium targets used for past plutonium production testing. Three of these targets were destructively characterized using Los Alamos National Laboratory actinide analytical chemistry capabilities. A validated conduct-of-operations protocol was followed for this characterization effort. Chemical analyses included measurements for radionuclides, uranium assay, uranium isotopic abundances, trace actinides, trace metals, and non-metals. Material scientists also examined materials for morphological and microstructural properties and individual particles were examined for trace impurities. After characterization of the targets was completed, a reactor modeling effort was undertaken to corroborate target details in historical records. Time since irradiation calculations utilized both activation and fission products. The described examination of uranium targets has a tremendous impact from a safeguards verification and nuclear forensics perspective.     

Partition layer-modified substrates for reversible surface-enhanced Raman scattering detection of polycyclic aromatic hydrocarbons

Herein, we present progress towards an analytical sensor for polycyclic aromatic hydrocarbons (PAHs) using surface-enhanced Raman scattering (SERS) on partition layer-modified nanostructured substrates. Specifically, a 1-decanethiol monolayer has been assembled on a silver film over nanospheres substrate to concentrate PAHs within the zone of SERS detection. Both anthracene and pyrene were detected with limits of detection at 300 and 700 pM, respectively. The measured SERS spectra allowed for easy distinction of the two PAH compounds, due to varying peak locations, and insight into the partitioning mechanism. Additionally, exposure to a common environmental interferant, Suwannee River fulvic acid, did not impede the measurement of the PAHs, and the sensor is reusable after a short exposure to 1-octanol. Finally, the utility of this sensing platform for PAH detection was compared to that achievable for other classes of organic pollutants such as polychlorinated biphenyls and polybrominated diphenyl ethers. Figure SERS detection of polycyclic aromatic hydrocarbons facilitated via partition layer modified substrates.

Scaling of the F2 structure function in nuclei and quark distributions at x>1

We present new data on electron scattering from a range of nuclei taken in Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the cross section for x>1, which is sensitive to short-range contributions to the nuclear wave function, and in deep inelastic scattering corresponds to probing extremely high momentum quarks. This result agrees with higher energy muon scattering measurements, but is in sharp contrast to neutrino scattering measurements which suggested a dramatic enhancement in the distribution of the "superfast" quarks probed at x>1. The falloff at x>1 is noticeably stronger in 2H and 3He, but nearly identical for all heavier nuclei.     

Lithium insertion studies on boron-doped diamond as a possible anode material for lithium batteries

Boron-doped diamond (BDD) was prepared by the hot filament chemical vapor deposition method. The prepared samples were subjected to X-ray diffraction, scanning electron microscopy, and Raman spectroscopy studies. The BDD composite electrode/Li cell has been assembled, and its cycling behavior was studied. The BDD possesses large sp² sites, which effectively participate in the lithium storage process. Furthermore, nanocrystalline tin (Sn) particles were prepared by the chemical reduction method. The addition of nanotin with the BDD-active material greatly enhances the cyclability of the cell. An erratum to this article can be found at     

Structural and optical property studies of CdSe crystalline nanorods synthesized by a solvothermal method

CdSe nanorods are synthesized via a simple solvothermal method at a moderate temperature of 180 °C. The influences of introducing hydrazine hydrate (N₂H₄·H₂O) as the reducing agent, and ammonia (NH₃·H₂O) as the complexing agent and also the reaction temperature, on the morphology and size of the obtained CdSe nanorods are investigated and reported. CdSe nanorods with a mean diameter and length of 25 and 82 nm, respectively, are synthesized and the problem of handling the stacking faults present in the long CdSe nanorods is analyzed. The use of increased quantity of hydrazine hydrate and also prolonged reaction time is found to reduce the stacking faults on the synthesized nanorods. The morphology, phase and the optical properties of CdSe nanoparticles are studied using powder X-ray diffraction, TEM and high-resolution transmission electron microscope (HRTEM), UV–visible absorption spectroscopy and photoluminescence (PL) spectroscopy. The low-resolution TEM images confirm the formation of CdSe nanorods, and also the agglomeration of nanoparticles and the presence of few spherical nanoparticles. The strong PL intensity from the CdSe nanorod at 702 nm confirms a blue shift of 14 nm, when compared with the bulk wurtzite CdSe.     

Combinatorial materials research applied to the development of new surface coatings: VIII: Overview of the high-throughput measurement systems developed for a marine coating workflow

A combinatorial workflow has been produced for the development of novel, environmental-friendly marine coatings. A particularly challenging aspect of the workflow development was the selection and development of high-throughput screening methods that allow for some degree of prediction of coating performance in the aquatic environment of interest. The high-throughput screening methods currently in place include measurements of surface energy, viscoelastic properties, pseudobarnacle adhesion, and a suite of biological assays based on various marine organisms. An experiment involving a series of fouling-release coatings was used to correlate high-throughput screening data to data obtained from ocean site immersion testing. The results of the experiment showed that both bacterial biofilm surface coverage and storage modulus at 30 °C showed a good correlation with barnacle adhesion strength and a fair correlation with fouling rating, but surface energy and pseudobarnacle adhesion did not correlate with the results from ocean site testing.     

Oxidation of thiocyanate by hydrogen peroxide - a reaction kinetic study by capillary electrophoresis

The oxidation reaction kinetics of thiocyanate by excess hydrogen peroxide has been studied by using capillary electrophoresis. The paper illustrates for the first time the use of capillary electrophoresis in studying reaction kinetics and provides a non-laborious way to determine the rate law and the rate constant for the above reaction in the pH range 6–8. Standard solutions of thiocyanate were mixed with buffer solutions of different pHs (6–8) and the reactions were initiated by adding appropriate volumes of hydrogen peroxide in capillary electrophoresis vials. Each reaction mixture was sampled at regular time intervals using an automatic injection programme to follow the progress of the reaction and identify the reaction products. The peak areas, representing the products, were integrated and their concentrations were quantified using calibration plots. The concentration profiles obtained from a series of experiments at a particular pH were then used to determine the rate law and the rate constant for the reaction. Furthermore, the rate of decomposition of hypothiocyanite formed during the reaction is determined for the first time. The rate law is zero order with respect to hypothiocyanite and first order with respect to hydrogen peroxide. The results indicate that the rate law for the oxidation reaction is zero order with respect to thiocyanate and first order with respect to hydrogen peroxide. The rate constant for the reaction at 25°C and at zero ionic strength is 3.6(±0.2)×10(⁻⁴) min⁻¹.     

Measurements of GnE/GnM from the 2H(e-->,en-->)1H Reaction to Q2=1.45 (GeV/c)2

We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G(n)(E)/G(n)(M), obtained via recoil polarimetry from the quasielastic 2H(e-->,e(')n-->)1H reaction at Q2 values of 0.45, 1.13, and 1.45 (GeV/c)(2) with relative statistical uncertainties of 7.6% and 8.4% at the two higher Q2 points, which points have never been achieved in polarization measurements.     

Phase transitions in CuS–Ag2S nanoparticle system

(Ag₂)_xCu_1?xS, x = .2, .4, .6 and .8 nanoparticles were synthesized by the solvothermal method. The as-synthesized nanoparticles were characterized by X-ray diffraction to study the crystal structure and size. The surface morphologies of the above samples were studied using scanning electron microscope. As there is continuous shift in the lower wavelength absorption edge of the UV–VIS spectrum of these samples with concentration, (Ag₂)_xCu_1?xS nanoparticles can be tuned to different band gap energies by varying the composition. The D.C. electrical resistance was measured in the temperature range 310–485 K. As Ag₂S transforms from monoclinic to bcc at around 450 K, copper sulfide nanoparticles also shows a phase transition at around 470 K, the effects of these two transitions are seen in the resistance measurements and in the UV–VIS spectra of the entire system. The electrical resistance of (Ag₂)_xCu_1?xS nanoparticles rapidly reduces as more and more copper sulfide is added.     

Normal micelle synthesis and characterization of MgAl2O4 spinel nanoparticles

Magnesium-aluminum oxide, MgAl₂O₄ spinel nanoparticles have been synthesized using normal micelle microemulsion methods. A mixed magnesium-aluminum hydroxide is initially formed which after annealing at 600°C forms nanocrystalline MgAl₂O₄ spinel. By controlling reactant concentration in the micelle solution, the particle size has been tuned over the range 4-20 nm. The reaction pathways have been determined by using the characterization methods such as X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry.