Positron diffusion in solid and liquid metals

Abstract

We made a systematic study of the diffusion of positrons in several liquid and solid metals with a vertical positron beam. Several interesting effects have been observed by studying the line shape parameter S, the fraction of positronium formed at the surface, and the diffusion length of positrons in liquids. The S parameter and the fraction of positronium created and released at the surface ͑F parameter͒ were measured as a function of temperature in the solid and liquid phases of Ga, Bi, Na, Sn, In, and Pb. An appreciable change just below or across the melting point in the S parameter was measured in metals where positron trapping has not been observed ͑Ga, Bi, and Sn͒. In metals where positron trapping occurs in the solid phase, there is a small change or none in the S parameter ͑Pb and In͒, which indicates that there is only a small change in the nature of the traps. Positron trapping was seen in all the liquid metals, indicating that they have a high density of defectlike sites that trap positrons. The diffusion length of positrons in the liquid was extracted from the experimental data. In Ga, Bi, and Sn, there is a large drop in the diffusion length upon melting; in Pb and In, only a small change or none is seen. In all liquid metals the diffusion length increases as the temperature increases, suggesting that diffusion is related to trapping in temporary fluctuations in the liquid's structure. The positron moves from fluctuation to fluctuation. The size of the traps strongly depends on temperature, and so when it increases, the positron's hopping motion increases. We also measured the reemitted energy spectra of positrons from liquid and solid surfaces. No appreciable change was seen with increasing temperature or when the metals melted.

Positron and Ion Migrations and the Attractive Interactions between like Ion Pairs in the Liquids: Based on Studies with Slow Positron Beam

“…From Fig.2, it is seen that eq. (5) is consistent with experimental results [15]. Now, we recall that the electro-hydrodynamic stress tenser S el .…”

“…The divergence of electical stress S el defines a local force density f which we write as Positron diffusion length versus temperature in the solid and liquid In and Pb metals. Open circles and solid circles correspond to experimental data points of In and Pb metals [15]. A dotted line is fitted one [23].…”

“…The sensitivity of positrons to changes induced by melting has already been reported by the positron annihilation angular correlation [9][10][11] and lifetime [12,13] studies for liquids. Gramsh et al [14,15] have observed very different behavior of the diffusion length L + of positrons in liquid and solid metals. That is, on melting, L + decreases remarkably, and in the liquid phase, L + increases with temperature.…”

Positron diffusion in the liquid metal phase

“…Based on an important idea of Kleman and Sadoc [6], it has been proposed that the parameter ρ(r,u) in two-dimensional and three-dimensional metallic liquids and glasses is specified by rigid-body rotation, which are related to gauge fields of SO(3) symmetry for S 2 and SO(4) symmetry for S 3 , respectively [6,7], one(I,K) of the present authors [8][9][10][11][12][13] has introduced the effective Lagrangian in the gauge-invariant formula with spontaneous symmetry breaking for two dimensional and three dimensional metallic liquids and glasses, and has discussed the origin of the boson peak, the glass transition, and the viscosity of the supercooled metallic liquids. Gramsh et al [14,15] have observed very different behaviours of the diffusion length L + of positrons in liquid and solid metals. That is, on melting L + decreases remarkably, and in the liquid phase, L + increases with temperature.…”

“…One(I.K) of the present authors [17,18] proposed a qualitative explanation for the increase with temperature of the positron diffusion length in liquid metals. In this study, we will analyze the positron diffusion length date in the liquid phase of In metal of Gramsch et al [15] from the view point of the restoration of the spontaneously broken density around the positron [17,18].…”