A.C. Lawson

Absence of magnetic moments in plutonium

Many theories published in the last decade propose that either ordered or disordered local moments are present in elemental plutonium at low temperatures. We present new experimental data and review previous experimental results. None of the experiments provide any evidence for ordered or disordered magnetic moments (either static or dynamic) in plutonium at low temperatures, in either the

Neutron powder diffraction refinement of boron carbides nature of intericosahedral chains

\ensuremath{\alpha}

The influence of oxygen content on the α to ω phase transformation and shock hardening of titanium

or

Melting of the light actinides

\ensuremath{\delta}

Structure and valence from complementary anomalous X-ray and neutron powder diffraction

phases. The experiments presented and discussed are magnetic susceptibility, electrical resistivity, nuclear magnetic resonance, specific heat, and both elastic and inelastic neutron scattering. Many recent calculations correctly predict experimentally observed atomic volumes, including that of

Magnetic neutron diffraction study of UGA3 and UGA2

\ensuremath{\delta}

Low temperature magnetic structures of UPdSn

-Pu. These calculations achieve observed densities by the localization of electrons, which then give rise to magnetic moments. However, localized magnetic moments have never been observed experimentally in Pu. A theory is needed that is in agreement with all the experimental observations. Two theories are discussed that might provide understanding of the ensemble of unusual properties of Pu, including the absence of experimental evidence for localized magnetic moments; an issue that has persisted for over 50 years.

Magnetic and crystallographic order in α‐manganese

Abstract Our Rietveld structure refinements of neutron powder diffraction data of boron carbides with 10, 13, 16, and 20 at.% carbon indicate 15–25% vacancies at the central position of the intericosahedral chains. In addition, we find a comparable number of interstitials residing off the intericosahedral chains. However, X-ray diffraction studies on unirradiated boron carbide single crystals do not generally find these defects. This discrepancy may indicate that the observed defects are the remnants of defect cascades created by the energetic fission products of 10 B during the neutron diffraction measurements. The tendency to form vacancies in the center of the intericosahedral chain is consistent with the weak and soft binding of chain-center atoms that we previously inferred from other measurements.

Invar model for δ-phase Pu: thermal expansion, elastic and magnetic properties

In this study the influence of alloy chemistry on the propensity of omega phase formation in two titanium alloys during shock loading is examined. The effect of peak shock stress on the phase stability and substructural evolution of high purity and A-70 (3700ppm oxygen) titanium was probed utilizing velocity interferometer system for any reflector and post shock substructural analysis. While in the high purity titanium the alpha to omega phase transformation was found to occur at 10.4GPa, no transformation was observed in the A-70 material for stresses up to 35GPa. Transmission electron microscopy analysis and neutron diffraction of shock-recovered samples confirmed these results and probed the details of twin and dislocation structures. Debye temperature data are also presented and the Debye-Waller temperatures for the alpha and omega phases in the high purity titanium are calculated. Finally, the compressive, quasistatic reload behaviors of both high purity and A-70 titanium are compared to the as-annea...

Thermal expansion and atomic vibrations of zirconium carbide to 1600 K

Abstract In this paper, we apply the Lindemann melting rule to the analysis of Debye-Waller factor data obtained by neutron powder diffraction for several light actinide phases. The anomalous melting points of the light actinides can be understood in terms of the temperature dependences of their elastic properties. We have extended the Lindemann rule to include temperature-induced elastic softening.