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Experimental data describing the equilibrium temperature dependence of positron annihilation in Cu, Ag, Au, Zn, Cd, Al and Pb are considered in terms of the simple trapping model. The results show that there is a correlation between a temperature, Tv, associated with the onset of measurable positron trapping at vacancies and the absolute temperature of melting, Tm, of the metal; Tv approximately 0.6Tm. The correlation may be shown to imply that the product of the specific trapping rate of positrons at vacancies, mu , and the mean positron lifetime, tau , characteristic of the bulk metal, is similar for each of these elements. Values of mu are then extracted from the data using vacancy concentrations based on a present assessment of parameters describing the temperature dependence of the equilibrium vacancy populations of these metals. It is found that values of the product, mu tau , are indeed similar, as indicated by the Tv/Tm correlation. The result can be qualitatively understood in terms of a theory of positron-vacancy interactions which suggests that changes in mu tend to be cancelled by opposite changes in tau .

Doppler-broadening measurements of positron annihilation in quenched single-crystal Al-1.5*10-2at%Si show a reversible temperature dependence of the annihilation characteristics which varies according to the defect state of the crystal. This effect seems to be largely able to account for an apparent discrepancy between data for quenched samples measured at 78K and at higher temperatures.

Measurements of the annihilation lineshape parameter between 100 and 300K in deformed nickel specimens of high purity reveal small positive temperature dependences for both the saturation trapping lineshape St and the trapping rate per unit defect concentration nu . The results disagree with recent predictions of a constant nu (T) for electron-hole-mediated trapping (MacKenzie et al., 1975).

Doppler broadening studies have been conducted on the gamma rays following annihilation of positrons in deformed copper samples. The trapping rate has been found to be independent of temperature.

The solution to a model problem representing positron trapping at defects in metals in the presence of positron-phonon scattering is presented. The model uses a separable form of the trapping interaction to allow the series expansion in the interaction to be summed exactly. This form of the trapping interaction is most suitable for well localised trapped states. A position representation is used, so that motion of the positron from point to point appears explicitly in the theory. In contrast to the predictions of classical theory, the aspects of positron motion that influence the trapping probability are relatively insensitive to positron-phonon scattering.

High precision measurements of positron lifetimes in indium have been carried out at five temperatures in the range 83K to 405K. Constraint free analyses of the results clearly establish the multicomponent nature of the lifetime spectra and the fitness of the 'no escape' models of positron defect trapping phenomena. The implications for positron studies of vacancy formation energy are discussed.

Theoretical calculations of the positron-vacancy binding energies in the BCC refractory metals Nb, Ta and W have been carried out using the authors' previously-developed supercell method (1977). The results indicate that the positron is sufficiently tightly bound to the vacancy in these metals that significant thermal detrapping is highly unlikely. Positron annihilation characteristics in the Bloch and vacancy-trapped states of the positron were also calculated for W. The general shapes of the core-electron contributions to the angular correlation curves in the two states were found to be different.

As the vacancy migration rate becomes higher than the positron annihilation rate at sufficiently high temperatures, the effect of vacancy migrations must be taken into account. The modified positron trapping model, with this included, yield values of 0.9 eV for vacancy movement activation energy, and 0.2 eV for divacancy binding energy in Cu.

A fully quantum mechanical theory is developed. The theory is applicable to strong as well as to weak trapping, and includes the effect of trapping on the positron distribution in the vicinity of the trap. Nonequilibrium many-body theory is used to formulate the problem in order to include positron annihilation in a natural way. It is concluded that for weak trapping the golden rule is applicable if an initial distribution of thermalised positrons including the positron-phonon interaction is used. For stronger trapping the lowest-order correction to the golden rule is calculated and the corresponding positron density is examined. The positron density around the trap is altered by the trapping process as time progresses, and this is illustrated by calculations of the time evolution of the positron density near a monovacancy.

Positron trapping at vacancies and precipitates in copper-indium alloys (3.3 at.% and 7.1 at.% indium) has been studied by positron annihilation measurements using the Doppler-broadening technique. The temperature dependence of the lineshape parameter F shows a strong deviation from the usual S-shaped curves. Difficulties in deducing vacancy formation enthalpies from the data are discussed. Isothermal annealing experiments allow the determination of the positron-precipitate binding energy Ee+b=0.16+or-0.05 eV as well as the migration energy for interdiffusion Em=0.62+or-0.08 eV during the precipitate growth.

The Doppler-broadened lineshape for electron-irradiated nickel shows a small positive temperature dependence between 100 and 300K. No such dependence has been observed in similar work by others.

The recovery of Cd deformed at 77 K has been studied by means of positron lifetime measurements. The results are interpreted on the basis of positron trapping and annihilation at jogs.