"Enhancement Factor" for Positrons in Sodium

Donaghy, J. J.; Stewart, Andrew

doi:10.1103/physrev.164.396

Cited by 48 publications

(6 citation statements)

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“…It is also convenient in that more experimental evidence relevant to the present study is available than for other alkali metals. For example, Fermi-surface measurements (Grimes & Kip, 1963;Shoenberg & Stiles, 1964), positron annihilation experiments (Donaghy & Stewart 1967) outer-electron momentum-density distribution experiments (Phillips & Weiss, 1968) and many other pieces of physical information indicate that sodium has the most nearly-free-electron-like character of all the alkali metals. On the other hand, sodium elastically is an highly anisotropic solid and it has a relatively low melting point and Debye temperature.…”

Section: Introductionmentioning

confidence: 99%

An X-ray study of thermal vibrations in sodium

Field¹,

Medlin²

1974

Acta Cryst Sect A

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A room-temperature X-ray study of Bragg reflexions from sodium metal crystals has been made. Six sets of integrated relative intensities were recorded photographically from two single crystals. Considerable anisotropy in the intensities has been found and it is suggested that this is due to anharmonic vibrations of the atoms. The data has been analysed in terms of a fourth-order atomic-potential expansion and values of an isotropic Debye parameter and an anharmonic anisotropic vibration parameter are given. The observed values of the available structure factors are presented. The accuracy claimed is 2 %.

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Section: Introductionmentioning

confidence: 99%

An X-ray study of thermal vibrations in sodium

Field¹,

Medlin²

1974

Acta Cryst Sect A

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“…3 6 In a typical experiment, incident x rays with fre-quency&&, wavevectork&, andpolarization &, are scattered into a small solid angle. The scattered x ray is described by the corresponding quantities z, k2, and e2 (see (2) where is the Thompson cross section. The momentum density N-is defined by, N;= (aa;), -…”

Section: Introductionmentioning

confidence: 99%

“…Equation (2) is valid as long as the energy of the x ray is small compared to mc but large enough which are, respectively, the energy and momentum transferred to the medium. In the so-called impulse approximation, ' the cross section is given so that the recoil energy 5 k /2m is much greater than the characteristic energies of the system being studied.…”

Section: Introductionmentioning

confidence: 99%

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X-Ray Compton Profiles of Li and Na: Theory and Experiments

Eisenberger¹,

Lam²,

Platzman³

et al. 1972

Phys. Rev. B

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A general discussion is presented of x-ray Compton profiles for conduction electrons in metals. A formalism that includes both the interelectron Coulomb interaction and the electronion interaction is then introduced. X-ray-scattering measurements of the Compton profiles of single-crystal Li and polycrystalline Na were carried out at room temperature. There is substantial agreement bebveen our experimental data and the theoretical predictions.

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“…In spite of the success in improving these features of Kahana's approximation, the form of the enhancement factor E ( P ) has not received much attention lately. The reason for this may be that the subsequent measurements of alkali metals (Melngailis and De Benedetti 1966. Donaghy and Stewart 1967, Kim and Stewart 1975 seemed to have confirmed Kahana's prediction for the dependence on r, of the ratios b/a, cja.…”

Section: Ro(p) = [Ro1(2)l2 @(Pf -P)mentioning

confidence: 74%

Hyperbolic Limit Sets of Evolutionary Equations and the Galerkin Method

Kamaev¹

1980

Russ. Math. Surv.

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The angular correlation of the two gamma quanta emitted when a thermalised positron annihilates with metallic conduction electrons is investigated by applying the newly developed theory in which an electron gas is considered as a system of interacting collective excitations. The conduction electrons are treated in a jellium model. The method leads in a natural way to the appearance of high-momentum components (i.e. pair momentum P > pF) in the annihilation radiation. The amount of these components is significant ( 2 lo",) in a dilute electron gas (such as in alkali metals), but fairly irrelevant for higher densities. The dependence on momentum of the enhancement factor for a dense system (wzith r, = 2 ) agrees well both with the earlier theories given b) Kahana and others, and also with recent accurate experimental observations. As r, increases into the alkali-metal region. the enhancement factor for P c. pF becomes relatively more and more constant, in contrast with the trend in the Kahana theory. In this density regime the experimental results vary widely. although most of them disagree with the present prediction. The additional effects due to core annihilation and lattice periodicity are studied and reviewed.

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"Enhancement Factor" for Positrons in Sodium

Abstract: Experimental data from positron annihilation in sodium single crystals show (a) that the Fermi surface is spherical and (b) that the momentum dependence of the "enhancement factor" of the polarization of the electron sea by the positron agrees with calculations.

Cited by 48 publications

References 8 publications

An X-ray study of thermal vibrations in sodium

An X-ray study of thermal vibrations in sodium

X-Ray Compton Profiles of Li and Na: Theory and Experiments

Hyperbolic Limit Sets of Evolutionary Equations and the Galerkin Method

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