[en] An 8-MeV ⁷Li⁺⁺ beam was used to implant 7.4 x 10¹⁵ atoms/cm² of lithium in each of a number of annealed, rolled niobium foils. After implantation the foils were individually heated at temperatures ranging from 250⁰C to 1730⁰C. The foils were then bombarded by a nanosecond-pulsed proton beam and lithium concentration profiles were deduced from measured time-of-flight spectra of neutrons produced by ⁷Li(p,n) reactions within the foils. Lithium distributions are not significantly affected by heating for several hours at temperatures up to 1400⁰C and, with 10 atomic parts per million, all lithium is confined to the implantation peaks. At about 1500⁰C the lithium begins to migrate preferentially toward the surface of the foil through which the lithium beam entered. Heating at 1710⁰C for one hour results in an average lithium concentration of roughly 20 ppM which is uniform to +- 20 ppM

[en] Lithium concentration as a function of depth below the surface of a solid of otherwise-known composition is determined by measuring neutron spectra from the ⁷Li(p,n)⁷Be reaction. Depths of the order of 50 μm are probed nondestructively in a single measurement with a depth resolution of a few microns or better depending on host materials and operating parameters. Sensitivity in the absence of background-producing materials can reach several atomic parts per million at 10% accuracy. Since at high concentrations measurements may be made in a few minutes, changes in lithium concentration caused by beam heating may be followed in real time

[en] Pulsed-beam, time-of-flight techniques are used to measure the energy dependence of a collimated, fast-neutron continuum transmitted through an object. By comparing results to similar measurements on pure elements, number densities of elements projected along the neutron beam path are deduced. The method is applied to a translate-rotate scan of an object ∝15 cm in diameter containing hydrogen, carbon, nitrogen, oxygen, phosphorus, and calcium. Techniques of computed tomography are then used to determine the spatial distribution of the various elements in a plane slice of the object. Several factors affecting precision and accuracy are discussed. (orig.)

[en] Several bulk samples ranging from chemical compounds to cereal grains have been nondestructively analyzed through neutron-attenuation measurements. A fast-neutron continuum was produced by an accelerator. Attenuations were measured by pulsed-beam, time-of-flight techniques. Average hydrogen, carbon, nitrogen, and oxygen contents were deduced by comparing attenuations to those measured for pure elements. Statistical precisions of 0.3-0.7 atomic percent were achieved for each element in about 10 min. Comparisons with results of other analysis techniques indicate that similar levels of accuracy are possible, even in the presence of small amounts of heavier elements. (author)

[en] Analyzing powers have been measured for the ⁶Li(n Vector, t)⁴He reaction for neutron energies between 0.2 and 1.4 MeV. An energy continuum of neutrons was produced by bombarding a thick lithium metal target with a 3.5-MeV, nanosecond-pulsed proton beam. The partially polarized neutrons emitted at 50⁰ were incident on an evaporated ⁶Li metal target. A silicon surface barrier detector was used to measure triton and α-particle yields as a function of particle energy. Tritons were distinguished from α particles with time-of-flight techniques. Yield asymmetries were determined at laboratory angles of 35⁰, 60⁰ and 80⁰ with angular resolutions of +- 5⁰. The α-particle yield asymmetries were converted to backward angle triton asymmetries, providing data at six angles. Analyzing powers as a function of angle were deduced. Although results are tentative, analyzing powers near 90⁰ and 250 keV are negative (approximately -0.3) while above 700 keV they are large and positive (approximately +0.9) and vary slowly with neutron energy. 4 figures

[en] Neutrons and X-rays are mathematically equivalent as probes in computed tomography. However, structure in the energy dependence of neutron total cross sections and the feasibility of using time-of-flight techniques for energy sensitivity in neutron detection suggest that spatial distributions of specific substances can be determined from neutron transmission data. We demonstrate that this is possible by tomographically reconstructing from such data a phantom containing several different structural materials

No abstract available

[en] Neon ions were accelerated to energies between 1.5 and 3.0 MeV. Pulse height distributions were measured with a silicon surface barrier detector both for directly incident ions and for ions transmitted through carbon foils. Detector line shapes are skewed with widths of about 100 keV (fwhm) and are not strongly dependent on energy or energy loss. The impact of line shapes on thickness resolution in energy-loss radiography is discussed. Information is developed for detector pulse height defect for neon ions and for neon ion stopping powers in carbon. (orig.)

[en] Differential cross sections for neutrons scattered from natural Pb and 99.9% isotopically pure ²³⁸U have been measured at 0.5⁰, 1.0⁰ and 1.5⁰. A neutron energy continuum was produced by bombarding a thick natural lithium target with a 4 MeV, nanosecond-pulsed proton beam. Neutron energies were determined by time-of-flight techniques. Flight paths from the neutron source to the scatterer and from the scatterer to the detector were each about 5 m. For the 0.5⁰ measurements an annular detector geometry with an angular resolution of +-0.1⁰ was developed to maximize detection solid angle. Data were averaged over 100 keV intervals from 0.6 to 2.2 MeV and were corrected for backgrounds, multiple scattering and inelastic scattering. Measured cross sections were compared to optical-model calculations which included electromagnetic interactions of neutrons with the nuclear Coulomb field. Inclusion of an induced neutron electric dipole moment interaction was not warranted by the data. The angular dependence of the cross section was fitted with a function A+B cot²1/2-theta at each energy. Mean values of B for ²³⁸U are in agreement with theoretical predictions. Values of B for Pb are apparently 15% too low. (Auth.)

[en] The branching fraction for the isospin-symmetry-hindered positron decay of ⁴²Sc to ⁴²Ca (1.837 MeV) was measured to be (6.3+-2.6)x10⁵ by observation of delayed γ-rays. This branch alone corresponds to a reduction of the superallowed ground-state Fermi strength by (0.043+-0.018)%. The ⁴²Sc sources were produced by the ⁴²Ca(p,n)⁴²Sc reaction at 7.7 MeV. The measured branching agrees with Coulomb-mixing calculations by Rappleyea and Kunz and by Towner, but is smaller than other calculations. This result is of interest in connection with the intercomparison of the superallowed 0⁺ → 0⁺ pure Fermi decays, which determine the effective vector coupling constant of nuclear β-decay. (Auth.)