Novel approach to study angular correlation of positron annihilation radiation

The momentum density of electrons and the Fermi surface are measured in metal lead by the technique of positron annihilation. The three-dimensional electron-positron momentum distribution is reconstructed from measurements of the two-dimensional angular correlation of positron annihilation radiation (2D-ACAR), followed by the image reconstruction technique based on a direct Fourier transformation. On the basis of the obtained experimental spectrum, the Fermi surface topology, the high momentum components (HMC), the enhancement effect, and the autocorrelation function are discussed. The obtained experimental results are in good agreement with theoretical calculations.

Angular correlation of positron annihilation radiation from electron-irradiated platinum and plastically deformed platinum

The electron momentum density and the Fermi surface in Cu are studied by a two‐dimensional angular correlation of positron annihilation radiation (2D‐ACAR). The three‐dimensional electron momentum density is reconstructed using the image reconstruction technique. The electron momentum density obtained in the extended zone scheme is reduced to that in the reduced zone scheme by using the Lock‐Crisp‐West (LCW) folding procedure. The Fermi surface in Cu is determined in the reduced zone scheme. The enhancement parameters and the autocorrelation function are compared with the theoretical calculations.

A general approach is outlined to predict the chemical compositions of solute nanoclusters embedded in materials with nearly free electrons. Based on the experimental results of the two-dimensional angular correlation of positron annihilation radiation and the corresponding theoretical calculations, we show that the Fermi surface (FS)--Brillouin zone interaction is a key to understand the chemical composition realized in solute nanoclusters because the presence of FS necks at zone boundaries causes a reduction in electron energy due to the band-gap effect.

A position-sensitive γ-ray detector for positron annihilation 2D-ACAR based on metal package photomultiplier tubes

Positron annihilation calculations have been performed on semiconductor alloys with the aim of studying the disorder effect on the electron momentum distribution in InAs x Sb1- x . The electron wavefunctions are calculated using the pseudopotential method within the virtual-crystal approximation with and without incorporating the disorder effect as an effective potential. The calculations of the positron wavefunctions have been made in an identical manner, employing the point-core approximation for the ionic potential. The shapes of the profiles indicate that the angular correlation of positron annihilation radiation along different crystallographic directions in InAs x Sb1- x is not sensitive to the disorder effect.

The three‐dimensional electron‐positron momentum densities in paramagnetic Cr and W are reconstructed from measurements of two‐dimensional angular correlation of positron annihilation radiations (2D‐ACAR) by the image reconstruction technique based on a direct Fourier transformation. The experimental momentum density for paramagnetic Cr and W shows the contribution of the Fermi surface sheets; the electron surface at Γ, the hole surface at H, the hole surface at N. The Fermi surface topology obtained from the present results agrees with the theory and other experiments.

Angular correlation of positron annihilation radiation is widely used in solid state physics studies (Goldanskii; Hautojärvi), in the defectoscopy of monocrystals in particular (Nielsen et al.). The interest to surface studies gave rise recently to very sophysticated and expensive method of positron beams (Goldanskii et al.). The recent study and recently published papers (Aravin et al.; Valiev et al.) demonstrate, however, that valuable information on surface properties can be obtained using the traditional angular correlation (AC) technique.

Electron-position momentum distribution measurements of high-Tc superconductors and related systems

Positron annihilation in superconductive niobium-aluminium alloys

Positronium Formation in Muscle: An Investigation of the Structure of Cell Water

A pseudopotential formalism is applied to calculate the angular correlation of positron annihilation radiations (ACPAR) along the (100), (110) and (111) directions in Ge. The results are found to agree very well with the measured data. Calculations show that the ACPAR line shapes, particularly in the low-momentum region, are very much influenced by the detailed nature of bonding. Two-photon autocorrelation functions corresponding to the above symmetry directions are also presented and some interesting conclusions are drawn regarding positron-electron many-body correlation effects.

The angular correlation of positron annihilation radiation (ACPAR) along different crystallographic directions in Si x Sn 1-x and Ge x Sn 1-x is calculated. We observe that the electron-positron momentum density increases rapidly with increasing Si and Ge content. The computational technique used here is based on the independent-particle model (IPM) coupled with the use of the electron pseudowave and the virtual crystal approximation (VCA) which incorporates compositional disorder as an effective potential. We also present the variation of the positron lifetime in these alloys.

Polarized positron annihilation in ferromagnetic gadolinium

The Fermi surface of the $A15$ compound ${\mathrm{V}}_{3}$Si has been determined by reconstruction from two-dimensional angular correlation of positron annihilation radiation. The Fermi surface is compared to the one obtained from ab initio self-consistent linear muffin-tin orbital band calculations and generally good agreement is found to within 2 mRy in the band structure. The results are compared with other experimental and theoretical data.