This review is concerned with the utilization of the positron-electron annihilation phenomenon in studies of the physics of condensed matter. The theory of the annihilation process is outlined, the importance of the two-photon mode of decay is established, and it is described how the observable results depend on the initial positron and electron states of the system. A brief account of the principal experimental techniques is included. Discussion of the complex nature of positron behavior in molecular substances suggests the particular value of investigations directed at the two photon pick-off mode of decay of the orthopositronium atoms that are formed in these materials. The possibility of positronium formation in ionic and metallic materials is also considered. The many important electron aspects of positron annihilation in metals are dealt with. The independent particle approach to the analysis of two photon angular distributions is discussed and illustrated. A survey of electronic structure investigations includes studies of polycrystalline and single crystal specimens. The relevance of angular correlation measurements in investigations of the Fermi surfaces of metals and alloys is discussed. More recently developed applications to the study of defected and disordered systems are dealt with. A preliminary account of the interpretation of multicomponentmore » lifetime spectra in terms of varying numbers of distinguishable positron states provides the basis for a discussion of studies of positron trapping by defects, voids. and surfaces in ionic and metallic solids, liquids and powders. (auth)« less

Positron studies of condensed matter

The Sudbury Neutrino Observatory.

Reviews the investigation of monovacancies and divacancies in or near thermal equilibrium at high temperatures. The use of positron annihilation for determining vacancy formation energies is covered in considerable detail and put into perspective relative to other methods (eg thermal expansion, self diffusion, nuclear magnetic resonance). The experimental techniques for studying the trapping of positrons at vacancies and the trapping model used for analysing the experimental results are reviewed. A detailed discussion in terms of ion core size valency, and vacancy relaxation is given of the trapping criteria for different metals. It is shown that the experimental results on the existence or nonexistence of positron trapping by vacancies are well accounted for by the theoretical ideas. The formation energies of monovacancies in metals obtained by the positron annihilation techniques are presented and compared with those obtained by other methods.

https://iopscience.iop.org/article/10.1088/0305-4608/3/2/003/pdf

Investigation of point defects in equilibrium concentrations with particular reference to positron annihilation techniques

By means of the new technique of sealed–source specimens the Doppler broadening of the positron–annihilation γM line has been investigated in the refractory metals V, Kb, Ta, Mo and W between 4·2 K and the melting points. Tho ' high-temperature S ' characteristic for positrons trapped at vacancies in thermal equilibrium was observed for Mo and W. In V, Nb and Ta the high–temperature vacancy effect is less developed and no saturation of the temperature variation of the γM lineshape can be seen. It is concluded that in the latter metals detrapping of positrons from vacancies has to be taken into account. The following mono–vacancy formation enthalpies H1vF (in eV) were determined: 2·1 ± 0·2 (V), 2·6 ± 0·3 (Nb), 2·8± 0·6 (Ta, 3·0 ± 0·2 (Mo) and 4·0 ± 0·3 (W). The vacancy migration enthalpies H1vM deduced from the present results, in combination with self–diffusion data, indicate that in the b.c.c. refractory metals vacancies become mobile only above room temperature. The existing annealing data are ...

High–temperature positron annihilation and vacancy formation in refractory metals

Vacancy concentrations in metals

The equilibrium lineshape for positrons annihilating in Cd shows an anomalous temperature dependence which complicates analysis for vacancy formation energies. The phenomenon, tentatively identified as trapping by transient dilatations, probably occurs in all metals.

A new equilibrium effect in positron trapping in metals

The threshold temperatureTt at which thermally generated vacancies produce measurable positron trapping is a linear function of the energy of self-diffusionQ. SinceQ is also linearly related to the vacancy formation energyE1vf, a measurement ofTt leads directly to a determination of the latter. It is possible to make a precise determination ofE1vf without approaching the melting point—a major advantage in dealing with refractories or with metals having a high vapour pressure in the solid state.

Vacancy formation energies from positron trapping measurements

Angular correlation of gamma rays from two-quantum positron annihilation has been investigated in seven metals: zinc, cadmium, indium, lead, tin, aluminum, and bismuth, over a range of temperatures...

I. K. MacKenzie

Papers

A new equilibrium effect in positron trapping in metals

Vacancy formation energies from positron trapping measurements

Some temperature effects on positron annihilation in metals

Radionuclide emitters for positron-annihilation studies of condensed matter

A coincidence technique for study of Ge(Li) detector profiles