Sensitivity of Orthopositronium Annihilation Rates to Density Fluctuations in Ethane Gas

Abstract

In this Letter we present results from a continuing series of experiments whereby positron annihilation techniques are used to investigate the influence of density fluctuations on the annihilation of orthopositronium (o-Ps) atoms formed in ethane gas. We present new results that are the first to show a complex dependence of orthopositronium annihilation rates (x o -Ps ) on the density of the gas over a wide range of densities at a temperature that is only about 1 K above the critical temperature of the gas. These results support the sensitivity of A 0 _ Ps to density fluctuations in ethane gas and allow us to study the application of a simple density fluctuation model to X 0 . Ps at sufficiently high densities of the gas that density fluctuations are expected to be large and highly correlated. The behavior of o-Ps annihilation rates has been reported recently as a function of density and temperature in methane 1 and ethane 2 gases. However, these measurements were made only for limited ranges of densities and temperatures of the gases. Nevertheless, they have indicated that the annihilation rates of o-Ps atoms in methane and ethane gases are sensitive to density fluctuations. Generally at low densities, o-Ps annihilation rates increase linearly with the density of the gas up to certain temperature-dependent values of gas density Orthopositronium annihilation rates have been measured in ethane gas for densities in the range 1.8 to 286 amagats at 306.4 K. The behavior of the measured annihilation rates at densities up to about 70 amagats can be explained in terms of a simple density fluctuation model. New features are observed at higher densities of ethane at 306.4 K.

Localization of a quantum-mechanical particle in classical simple fluids

“…(15) Omitting f (r) at the first step of iteration, a nonlinear Schrodinger equation is obtained, since u0(r) is given in terms of the wave function g(r) which satisfies the necessary boundary and normalization conditions. This nonlinear Schrodinger equation can be solved with the Runge-Kutta method or the Adams-Bashfourth-Moulton schemes [19].…”

“…McNutt [15] have suggested a semiempirical model which explains the reduction of the annihilation rate in terms of fluid density fluctuations. This model fails in higher density region, where the localization effects are expected to be predominant.…”

A multi-state model for the density dependence of ortho-positronium annihilation rate in gases

“…The problem of the transition region from delocalised to localised behaviour is probably associated with spontaneous density fluctuations in the fluid. A simple model based on macroscopic thermodynamical arguments has been proposed and applied to several gases (McNutt and Sharma 1978, Sharma et al 1982, Tuomisaari et a1 1986, 1988b, Kawaratani et a1 1985. The model seems to be in accord with the experimental results at the transition region, where the fluctuations are expected to be most important.…”