Positron Annihilation Angular Correlation Research Articles

Positron annihilation angular correlation measurements in disordered systems: α brass

We performed angular correlation measurements of positrons annihilating in αCuZn single crystals. The orientation of the specimens was parallel to the (100), (110) and (111) directions. The results are compared with a model calculation for the Fermi surface of this alloy, assuming that every Zn atom adds two electrons to the total number of conduction electrons. The cross-sectional areas normal to the (100), (110) and (111) axes of the Fermi surface constructed in this way are compared with the experimental data. According to the evidence and conclusions in Ref. [1], we interpret the experimental results in terms of the topology of the Fermi surface. For a 77·7% Cu 22·3% Zn concentration alloy we find a radius for the necks along the (111) directions of 0·27±0·02 in units of the Fermi momentum.

Influence of electron irradiation on the narrow component in the angular correlation of positron annihilation in a quartz crystal

A narrow component in the angular correlation annihilation quanta in quartz crystals is indicative of a new process of positron annihilation. The intensity of that component decreases when color centers are created in the crystal by electron irradiation and is restored after bleaching.

Positrons annihilating in hexane and decane

In a previous paper (1), we calculated the momentum distributions of electrons in the C-C and C-H bonds using SCF valence bond electron wave functions. When these calculations were compared with experimental distributions of hexane and decane obtained from positron annihilation angular-correlation experiments, good fits were obtained for all but the high-momentum region. This discrepancy may be a t t r ibuted to the use of a constant positron wave function in the calculation. In this paper, we present the calculated momentum distr ibutions of photon pairs due to positrons annihilating with electrons in hexano and decane employing a positron wave function, which takes into account the interaction between a positron and the effective atomic nuclei, introduced by us (3) in calculations for positrons annihilat ing in solid and liquid methane. The calculation of the momentum distr ibution of the annihilating positron-electron pairs in the C-H bond, N(C-H), has been carried out in detail by CHUA~G et al. (2). The calculation of the momentum distr ibution of the annihilating pairs in the C-C bond, N(C-C), is similar to tha t of the iV(C-H), and the result is presented as follows:

MOMENTUM DISTRIBUTIONS OF TWO PHOTON ANNIHILATING POSITRON–ELECTRON PAIRS IN HEXANE AND DECANE

Momentum distributions are calculated for electrons in the C–C and C–H bonds in hydrocarbons, using analytic SCF functions for atomic carbon orbitals and Heitler–London-type functions for the two paired electrons in the C–C and C–H bonds. The positron wave function is assumed to be a constant. The computed momentum distributions are then compared with high-precision experimental distributions obtained from positron-annihilation angular correlation experiments.

Angular Correlation of Positron Annihilation in Teflon

The angular correlation of the 2-quantum decay of positrons annihilating in a Teflon absorber has been measured at room temperature and at 490\ifmmode^\circ\else\textdegree\fi{}K, in each case with a magnetic field of 10 kilogauss and in the absence of the field. The results are consistent with prediction based on the assumption of conversion between triplet and singlet states of positronium.