John Swinton King

Phonon dispersion and phonon densities of states for ZnS and ZnTe

Neutron scattering data are reported for II–VI zincblende crystals, which are believed to be of sufficient precision to refine earlier ZnS ambiguities and to provide a basis for model fitting comparable to existing III‐V results. Valence shell models, including 9–12 parameters (VSM) and a variable shell charge extension (VCM), were fit to the data and used to generate phonon density of states and Debye temperatures. Very good fits to the neutron data were obtained, but no model was found that also predicts an accurate set of electric and mechanical constants. It is concluded that an unambiguous ionic charge Z cannot be assigned from the neutron results in either case.

SANS measurements of deuterium-dislocation trapping in deformed single crystal Pd

Abstract Small-angle neutron scattering (SANS) measurements have been made on deformed, single crystal Pd at room temperature. Low concentrations of deuterium were introduced to observe dislocation-deuteron interactions. Two different deformation procedures (cold working by rolling and hydride cycling) were used in an attempt to compare dislocations with different substructures. The data appear to fall naturally into an intermediate Q and a Q region. The intermediate Q region is well described by a 1 Q model, which yields effective trapping radius, Ro, and trapping efficiency, ρD/ρd (the number of deuterons per A of dislocation line). The trapping radii for both sample types are approximately 11 A but the efficiencies differ by a factor of 2 or more. The conclusion is that in both cases the majority of trapped deuterons lie within a few Burgers vectors of the dislocation cores, but the trapping efficiency is significantly larger for the relatively uniform hydride cycled substructure than for the cold worked substructure. This we attribute to stress compensation from neighbouring dislocations in a cell-wall environment characteristic of the cold worked substructure. In the lowest Q region, the cross section for the cycled samples diverges from that of the cold worked sample, indicating a long rang trapping in the stress field of the former which is absent in the latter. In both Q regions, therefore, trapping is enhanced for the cycled dislocation substructure.

Lattice dynamics of cubic zinc sulfide

Abstract Dispersion curves for the acoustic phonons have been measured in the [100], [111], and [110] directions by neutron scattering. The zone boundary frequencies have been used to reassign multi-phonon events previously reported from infrared and Raman spectra. The data are compared with a preliminary six-parameter valence force model.

Neutron Scattering in Normal and Deuterated Polyethylene

The one‐ and two‐phonon amplitude‐weighted directional frequency functions are calculated for normal and deuterated crystalline polyethylene. These results are compared to previously measured frequency spectra for stretch‐oriented normal polyethylene and to new measurements on deuterated polyethylene. In addition, the Debye‐Waller factors are calculated for oriented polyethylene and compared with elastic‐scattering data.

Rapid inverting of the polarization of a neutron beam using large amplitude oscillating magnetic fields

Abstract During the course of designing and constructing a pulsed-neutron-polarization-inverter (PNPI) to be used in the study of magnetic excitations in solids, it was necessary to re-examine the oscillating field method of magnetic resonance in the region where the amplitude of the rf field B1 is comparable to the dc field B0. It is found that the phase of the rf field at the instant the neutron enters the spatial region of the field becomes an increasingly important considerations as B 1 B 0 becomes comparable to 1. Analog and digital computer solutions are given for the equations of motion of the neutrons magnetic moment in the presence of various field configurations important in the construction of a PNPI.

Improvements in the design and analysis of the segmented expanding mandrel test

Abstract The segmented expanding mandrel test is modified and improved to yield more quantitative information on the local stress and strain concentrations in Zircaloy tubing samples. The experimental apparatus has undergone changes in segment design, end restraint fixture design and the method of sample heating. These changes result in localization of stress and strain concentrations to known locations in the tubing, the introduction of a small degree of biaxiality and a more uniform sample temperature, respectively. A chamfered specimen design has been introduced for the purpose of producing a near plane-strain condition. Finite-element analysis has been added to provide information on the magnitude of localized stresses and strains given the sample geometry, test procedure and measured diametral strains. The resulting test represents a significant increase in the quantitative information produced in the segmented expanding mandrel technique.

Multiple scattering in small-angle neutron scattering measurements on polymers☆

Abstract Multiple scattering corrections in small-angle neutron scattering experiments on polymers have been examined. Numerical calculations show that, for typical experimental conditions, the second-order scattering is less than 2% of the first-order scattering for QR g up to 10.0. An approximate expression is also given for obtaining a rough estimate of the second-order scattering without numerical calculation.

SANS measurements of deuteride (hydride) formation in single crystal Pd

Abstract In situ small-angle neutron scattering (SANS) measurements of deuteride precipitation in well-annealed, undeformed single crystal Pd have been performed at room temperature to observe the morphology of the precipitate as the deuterium fraction was increased over a range of 0.005 to 0.097 [D]/[Pd]. Supporting measurements were made of the room temperature deuterium solubility isotherm in the single crystal material and of the progressive lattice mosaic broadening by gamma-ray diffraction analysis. The use of single crystal material eliminated the effect of grain boundaries on the precipitation process and allowed the orientation of the deuteride precipitates relative to the host Pd lattice to be established. The SANS data for deuterium loading beyond the solid solution phase are dominated by a d Σ /d Ω ∼ Q −2 scattering response well fit by a model cross section of small plate-like precipitates with a thickness of 25–30 A. This response showed little indication of a preferred habit plane and the plate thickness was independent of the total deuterium loading. The volume fraction of these small plates grew uniformly with increased deuterium loading, but was surprisingly small, reaching only 8×10 −5 at 0.060 [D]/[Pd]. This means that almost all of the deuterium resides in some other precipitate structure. The SANS data in the lowest Q region showed a second, anisotropic scattering component that can be interpreted as the Porod tail from plate-like particles of grossly larger dimensions. These plates favor a (001) α habit plane, normal to the elastically soft [001] α direction. Post-measurement visual inspection of the sample surfaces showed the presence of an oriented, quasi-periodic one-dimensional array of plates with thicknesses of approximately 0.1 to 0.2 mm and with an orientation in agreement with the anisotropy of the SANS data. We conclude that most of the deuteride phase precipitates in these large structures.

The influence of localized stresses and strains on the iodine scc behavior of Zircaloy-2 tubing

Abstract The segmented expanding mandrel test is modified to provide additional information on the localized stresses and strains during ramp-hold tests. A chamfered specimen is designed with four flats on the outer diameter for the purpose of creating sectors of variable wall thickness which establishes a more nearly plane strain state in the thinnest-gauge sections. Ramp-hold tests conducted in 40 MPa of iodine at 325°C show that at a measured diametral strain of 0.8%, chamfered specimens fail while regular tubing specimens require diametral strains of 2% or greater for failure. Calculations made with a two-dimensional, finite elements code show that at a measured diametral strain of 0.8%, the local strains in the clad ID over the segment interfaces are nearly identical for the regular and chamfered samples while the local stress in the chamfered sample is 15% greater. Results suggest that the smaller diametral failure strain of the chamfered specimen at low measured diametral strains is mainly due to its near plane strain condition and the higher hoop stresses resulting therefrom.

Nuclear fusion from crack-generated particle acceleration

SummaryIn summary, the high-voltages necessary to accelerate deuterons to energies sufficient to produce modest numbers (104–105/sec) of d-d neutrons appears to be possible as a result of cracking or “fracture” of the metal lattice in the “cold” fusion experiments.This mechanism requires neither “massive” electrons nor “exotic” nuclear reactions to explain the apparent “cold” fusion d-d neutron production results. Instead, it is possible that high voltage electrostatic fields, known to be associated with cracking, can reside across a crack gap long enough for the deuterons to be accelerated to sufficiently high energy to produce the d-d reactions. Interestingly, the electrostatic acceleration is quite similar to that of laboratory accelerators except for its submicron scale. Clearly, much work is still required to determine whether such a crack-generated acceleration mechanism, a “quasi-particle” mechanism, some combination of these, or some other, as yet unidentified mechanism is responsible for the nuclear effects seen in “cold” fusion experiments.