Since the sample container represents one of the earliest and potentially one of the largest sources of sample contamination, much of the analytical accuracy will depend upon the choice of container materials and the method of cleaning containers. Twelve different plastics have been examined by gravimetry, isotope dilution mass spectrometry, and neutron activation analysis. The present study examines the levels of impurities present in the various plastics as well as the quantities of impurities leached from the plastics by acid cleaning. A suggested method of cleaning containers is presented.

137Cesium and other contaminants have leaked from single-shell storage tanks (SSTs) into coarse-textured, relatively unweathered unconsolidated sediments. Contaminated sediments were retrieved from beneath a leaky SST to investigate the distribution of adsorbed 137Cs+ across different sediment size fractions. All fractions contained mica (biotite, muscovite, vermiculatized biotite), quartz, and plagioclase along with smectite and kaolinite in the clay-size fraction. A phosphor-plate autoradiograph method was used to identify particular sediment particles responsible for retaining 137Cs+. The Cs-bearing particles were found to be individual mica flakes or agglomerated smectite, mica, quartz, and plagioclase. Of these, only the micaceous component was capable of sorbing Cs+ strongly. Sorbed 137Cs+ could not be significantly removed from sediments by leaching with dithionite citrate buffer or KOH, but a fraction of the sorbed 137Cs+ (5-22%) was desorbable with solutions containing an excess of Rb+. The small amount of 137Cs+ that might be mobilized by migrating fluids in the future would likely sorb to nearby micaceous clasts in downgradient sediments.

On the morning of July 16, 1945, the first atomic bomb was exploded in New Mexico on the White Sands Proving Ground. The device was a plutonium implosion device similar to the device that destroyed Nagasaki, Japan, on August 9 of that same year. Recently, with the enactment of US public law 111-140, the “Nuclear Forensics and Attribution Act,” scientists in the government and academia have been able, in earnest, to consider what type of forensic-style information may be obtained after a nuclear detonation. To conduct a robust attribution process for an exploded device placed by a nonstate actor, forensic analysis must yield information about not only the nuclear material in the device but about other materials that went into its construction. We have performed an investigation of glassed ground debris from the first nuclear test showing correlations among multiple analytical techniques. Surprisingly, there is strong evidence, obtainable only through microanalysis, that secondary materials used in the device can be identified and positively associated with the nuclear material.

No abstract

Coherent quasielastic neutron scattering has been used to investigate the character of the rotational dynamics in the high-temperature solid phase of C6o. The observed scattering can be described by a model in which each molecule undergoes rotational diffusion which is uncorrelated with the motions of adjacent molecules. The rotational diffusion constant DR is (I.4±0.4)x I0'^ s~' at 260 K and (2.8 ±0.8)X 10'^ s~' at 520 K. The temperature dependence of DR is consistent with a thermally activated process having an activation energy of 35 ± 15 meV. 36.90.+f, 82.80.Jp C60 (buckminsterfullerene) forms a mostly orientationally ordered [1] simple cubic phase belonging to the space group Fa2> [2] below -255 K. Near this temperature it undergoes a transition [3] to a face-centered-cubic phase which is an excellent example of a broad class of molecular solids, sometimes termed "plastic crystals," which exhibit rapid molecular reorientations [4,5]. Quasielastic neutron scattering is capable of determining both the time scale of reorientations and, more importantly, the detailed nature of the reorientations [6]. Here we present such a study of the rotational dynamics of C6o in the orientationally disordered, high-temperature phase and show that the observed scattering is well described by a model in which there are no intermolecular correlations, and each molecule reorients completely randomly, as opposed to jump rotations between a specific set of sites.The sample consisted of -2.5 g of powdered Ceo of which 1.5 g were prepared at the University of Pennsylvania and 1.0 g at Exxon, using standard methods [7,8]. After the chromatographic separation of Ceo from the Ceo-Cyo extract, great care was taken to remove the solvent, since neutrons are -15 times more sensitive to hydrogen than to carbon. Prompt gamma activation analysis [9] showed a hydrogen content of 0.008 ± 0.002 atom per C atom for the Exxon sample and 0.0057 ±0.0011 atom per C atom for the Penn sample. Scattering from the H in the residual solvent was observed in our experiments, but does not affect our conclusions.The neutron scattering results were obtained using triple-axis spectrometers at the Neutron Beam Split-Core Reactor (NBSR) at NIST. For scattering vectors, g, below about 4.0 A~\ the neutrons were monochromated and analyzed using the (002) reflection of pyrolytic graphite. Collimators having angular spreads of 10'-20'-20'-20' were placed before and after both crystals, resulting in a measured energy resolution of 0.50 meV full width at half maximum (FWHM) at the elastic position. To reach larger values of g a shorter wavelength was necessary. In order to maintain a relatively good energy resolution, the Cu (220) reflection was chosen to monochromate the beam and the graphite (004) reflection was used to analyze the energy of the scattered neutrons. Combined with collimations of 40'-40'-40'-40' , this resulted in a measured resolution of 1.2 meV FWHM. For measurements in the fixed final energy configuration, the data were corrected for the separately m...

A permanent, full-time instrument for prompt-gamma activation analysis is nearing completion as part of the Cold Neutron Research Facility (CNRF). The design of the analytical system has been optimized for high gamma detection efficiency and low background, particularly for hydrogen. Because of the purity of the neutron beam, shielding requirements are modest and the scatter-capture background is low. As a result of a compact sample-detector geometry, the sensitivity (counting rate per gram of analyte) is a factor of four better than the existing Maryland-NIST thermal-neutron instrument at this reactor. Hydrogen backgrounds of a few micrograms have already been achieved, which promises to be of value in numerous applications where quantitative nondestructive analysis of small quantities of hydrogen in materials is necessary.

Gamma-ray spectra were taken up to 11 MeV from a wide range of samples and elemental standards while under neutron Irradiation to determine the elements whose prompt y rays are observable and can be used for analytlcal measurements.Up to 17 elements from among the set H,

No abstract