Magnetic Compton scattering study of the magnetocaloric material Gd(7)Pd(3).

The spin-dependent momentum density of Gd(7)Pd(3) was probed by the magnetic Compton scattering technique with elliptically polarized synchrotron radiation. A contribution to the spin moment from Pd 4d electrons was observed, at 2 and 280 K, alongside a large Gd 4f moment and a smaller Gd 5d moment. The total spin moment, at 2 K, was determined as 50.8 ± 0.7 µ(B) (f.u.)(-1). The Gd 4f contribution to the spin moment was determined as 43.4 ± 1.8 µ(B) (f.u.)(-1), the Gd 5d moment as 4.4 ± 0.7 µ(B) (f.u.)(-1) and the Pd 4d spin moment contribution as 2.9 ± 1.1 µ(B) (f.u.)(-1), where f.u. represents a formula unit. At 280 K the total spin moment was 27.3 ± 0.9 µ(B) (f.u.)(-1) with individual contributions determined as a Gd 4f spin moment of 23.8 ± 1.1 µ(B) (f.u.)(-1), a Gd 5d contribution of 2.2 ± 0.5 µ(B) (f.u.)(-1) and a Pd 5d spin moment of 1.2 ± 0.6 µ(B) (f.u.)(-1).

In situ measurements of the sub-surface gamma dose from Chernobyl fallout.

Methods of estimating external radiation exposure of soil-dwelling organisms are currently of much research and regulatory interest. In this paper, we report the first in situ measurements of the sub-surface gamma dose rate for 137Cs contaminated land that quantify variation in dose rate with depth. Two contrasting sites have been investigated. The first site comprised a mineral type soil with a low percentage of organic matter and the second site chosen was in a peat-bog. The different soil compositions afford different 137Cs mobility and this results in variations in the measured gamma dose-rate with soil depth. For each site the paper reports the measured dose rates, the 137Cs activity depth profile, the 137Cs inventory and a description of the soil-characteristics. It is suggested that these data can be used to produce estimates of the sub-surface gamma dose rate in other sites of 137Cs contamination.

A new method to account for the depth distribution of 137Cs in soils in the calculation of external radiation dose-rate.

This work reports a new method for calculating the external dose-rate as a function of height above land that has been contaminated with a surface deposition of (137)Cs. Unlike previous work this method accounts for vertical migration of (137)Cs using the Advection Dispersion Equation (ADE) with appropriate parameters. The results have been successfully verified with field measurements from the (137)Cs contaminated regions within the Republic of Belarus. The method also correctly predicts the observed variation of dose-rate with elevation above the soil surface and it is shown how this method can be used to predict the reduction in surface dose-rate after remediation measures such as deep ploughing have taken place.

High-energy magnetic compton scattering from iron.

The magnetic Compton profile of Fe [111] was measured using circularly polarized synchrotron radiation at incident energies of 84.4, 167.2 and 256.0 keV on the high-energy beamline at the European Synchrotron Radiation Facility. It was found that the momentum resolution of these experiments, which use semiconductor detectors, improves by almost a factor of two over what was previously possible by this technique at photon energies of approximately (1/10)mc(2). It was also observed that all three spectra reduced to the magnetic Compton profile, describing the spin-dependent ground-state momentum density, and that within the experimental error the integrated intensity of the magnetic effect scaled as predicted by the cross section derived in the limit of energies much less than the rest energy of the electron. The magnetic Compton profile of Fe [111], measured using 167.2 keV incident energy and with momentum resolution of 0.42 a.u., was compared with the prediction from a full-potential linearized augmented-plane-wave model profile. The fine structure predicted by theory was confirmed by the experimental profile at this improved resolution.

The spin dependent momentum density of hexagonal close packed cobalt.

Directional-spin-dependent Compton profiles of ferromagnetic hexagonal close packed cobalt metal have been measured with 117 keV and 167 keV circularly polarized synchrotron radiation at the new ESRF high energy beamline. Significantly improved resolution was achieved at the higher energy. The results have been compared with the profile predicted from an augmented plane wave (APW) calculation of the electron momentum density in the hexagonal phase. No significant difference was found between the c-axis and the basal plane magnetic profiles. The experiments show that there is substantially more 3d spin density at high momentum than in the model calculation. After correcting for this deficiency we find that the 4s-p component of the momentum density remains significantly different than predicted.

Final-state effects in neutron Compton scattering measurements on zirconium deuteride and beryllium.

We report inelastic neutron scattering measurements of the neutron Compton profile, J(y), for Be and for D in polycrystalline [Formula: see text] over a range of momentum transfers, q between 27 and [Formula: see text]. The measurements were performed using the inverse geometry spectrometer eVS which is situated at the UK pulsed spallation neutron source ISIS. We have investigated deviations from impulse approximation (IA) scattering which are generically referred to as final-state effects (FSEs) using a method described by Sears. This method allows both the magnitude and the q dependence of the FSE to be studied. Analysis of the measured data was compared with analysis of numerical simulations based on the harmonic approximation and good agreement was found for both [Formula: see text] and Be. Finally we have shown how [Formula: see text], where V is the interatomic potential, can be extracted from the antisymmetric component of J(y).