One-phonon coherent neutron scattering from certain polycrystalline materials

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32012/1/0000054.pd

Sans measurement of deuterium trapping at dislocations and grain boundaries in palladium

Small angle neutron scattering (SANS) measurements have been made on deformed single crystal and polycrystalline palladium with and without deuterium dissolved in the solution phase at room temperature. The net scattering cross section for the same sample with and without deuterium loading shows a behavior expected from deuterium correlation with dislocations forming rod-like scattering structures. We conclude from these scattering measurements that the trapped deuterium is within 2-3 Burgers vectors of the dislocation core. On average 1-3 deuterons per A are trapped at dislocations in the deformed samples. The measurements indicate the straight, rod-like correlation geometry extends on average 50-100 A along the dislocations. Net scattering from a well annealed polycrystalline palladium sample exhibiting a behavior expected from surfaces has been observed. This net scattering is attributed to deuterium trapped at grain boundaries in the polycrystalline sample. A value of 0.4 +/- 0.2 trapped deuterons per A2 of grain boundary area is calculated from the well annealed polycrystalline scattering measurement.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29076/1/0000111.pd

Chemical binding effects on resonant scattering of neutrons

Earlier calculations of the chemical binding effect on neutron resonance broadening do not agree with experimental results. A possible source of this difference is that the calculations have only examined the effect of chemical binding on resonant absorption and have not investigated the effect on resonant scattering. It is vital that we understand the discrepancy between the computed and measured chemical binding effect. Therefore the resonant differential scattering cross section is calculated for a harmonic crystal model to examine the chemical binding effect for resonant scattering. We show that, at high temperatures or high resonance energies, scattering can be treated using ideal gas with the same effective temperature as for absorption accounting for chemical binding effects. Although the resonance broadening is determined in terms of a four-point correlation function, it is found that this broadening can still be written in terms of the usual [psi]-function and the effect of chemical binding in both resonance absorption and scattering is not large enough to account for the large measured effect. Thus the experiments that show a substantial amount of chemical binding must be reevaluated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28844/1/0000679.pd

Méthodes quasi classiques pour particules avec spin

The key concepts of the quasi-classical theory of Wigner are reviewed. In particular, the concepts of the Wigner distribution and the Wigner equivalents for operators of position and spin are presented. Then, the Groenewold multiplication rule is applied to the Heisenberg equation of motion and to certain correlation functions. Finally, these concepts are applied to the général problem of spin corrélations and the spin position interaction.La théorie quasi classique de Wigner est passée en revue. On présente les concepts de la fonction de distribution de Wigner et des fonctions équivalentes de Wigner pour les opérateurs de position et de spin. L'emploi de la règle de multiplication de Groenewold est appliqué aux équations pour les opérateurs d'Heisenberg et les fonctions de corrélation. Finalement, ces concepts sont appliqués au problème général des corrélations des spins et à l'interaction des spins et des positions

SANS (small angle neutron scattering) measurement of deuterium-dislocation correlation in palladium

Small angle neutron scattering (SANS) measurements have been made on deformed polycrystal palladium samples with and without deuterium dissolved in the solution phase ({alpha}) at room temperature. Concentrations were held constant during SANS experiments by an equilibrium gas pressure cell. The difference scattering cross section for the same sample with and without deuterium loading has a 1/Q behavior (Q=4{pi}/{lambda} sin{theta}/2) at intermediate values of Q. At very low values of Q the dependence is much stronger than 1/Q. The 1/Q behavior is attributed to deuterium trapping close to long dislocation cores forming rod-like scattering structures

Dislocation-hydrogen correlation in metals

We present a method using SANS experiments to measure correlation between dislocations and absorbed hydrogen in metals. The technique involves sequential measurements first on a metal with dislocation networks, then two further measurements on the same sample infused with deuterium and normal hydrogen. SANS experiments on metals with dislocations networks have been performed a number of times and some results have appeared in the literature. We have computer estimates of the contribution of absorbed hydrogen and deuterium to SANS cross sections. The results show that we can expect to see the hydrogen contribution in the SANS cross section and see any possible correlations of the hydrogen positions and the dislocations. 8 refs., 2 figs., 2 tabs