Simulation of positronium: Toward more realistic models of void spaces in materials

Abstract

An exact treatment of the positron and electron in a two-chain, Path Integral Monte Carlo (PIMC) simulation is used to calculate both self-annihilation and pickoff rates at finite temperature. It has already been demonstrated that this technique can reproduce and extend results of simple theories of positrons and positronium (Ps) in spherical voids. Here, we include the effect of the linear dielectric response of a homogeneous material on the annihilation rate of positrons and Ps. In addition, we find lifetimes and structural information for Ps in cylindrical channels, both with and without adsorbed fluid atoms.

Local Free‐Volume Distribution from PALS and Dynamics of Polymers

“…The diameter of the Ps atom is 0.106η Ps −1/3 nm. The value of η Ps is not well known but is probably near 1 [Dupasquier, 1985;Bug et al, 2007].…”

“…Extension of the Tao-Eldrup model to other hole shapes (cubes, cuboids, cylinders) and large holes (here at finite temperatures, not only the ground state is occupied) is described in the literature [Jasińska et al, 1996;Goworek et al, 1997Goworek et al, , 1998Gidley et al, 1999] and discussed in Chapter 10. Modified models that consider different potential shapes have also been discussed [Dauwe et al, 2000;Bug et al, 2007].…”

Analytical evidence for quantum states in aqueous vanadium pentoxide with positron lifetime spectroscopy

“…Applying the model of fluid-filled pores [23], [24] as the self-annihilation rate kΓ 0 and pick-off annihilation rates from fluid Γ p.o.f luid and pore walls Γ p.o.wall , we can consider the summary annihilation rate as…”

Competitive positron and positronium trapping in porous media

“…By all those models, the radius (R) of the free volumes (whether spherical, cylindrical or cuboid) is related to the resulting lifetime of the o-Ps, thus providing one with a unique method to determine nanoscale-size Ps trapping sites (i.e., intrinsic or extrastructural free volumes) in a range of 0.1-10 nm. It is a positive development that ab initio calculations have already been started to calculate the free volumes (Bug et al, 2004) and estimation of lifetimes is being targeted also for cases when liquids are present in the voids (Bug et al, 2005).…”