ANTICOOL: Simulating positron cooling and annihilation in atomic gases

Abstract

The Fortran program ANTICOOL, developed to simulate positron cooling and annihilation in atomic gases for positron energies below the positronium-formation threshold, is presented. Given positron–atom elastic scattering phase shifts, normalised annihilation rates Zeff, and γ spectra as a function of momentum k, ANTICOOL enables the calculation of the positron momentum distribution f(k,t) as a function of time t, the time-varying normalised annihilation rate Z̄eff(t), the lifetime spectrum and time-varying annihilation γ spectra. The capability and functionality of the program is demonstrated via a tutorial-style example for positron cooling and annihilation in room temperature helium gas, using accurate scattering and annihilation cross sections and γ spectra calculated using many-body theory as input. Program summaryProgram title:ANTICOOLProgram Files doi:http://dx.doi.org/10.17632/kjstc6xskg.1Licensing provisions: GPLv3Programming language: Fortran 90Nature of problem: Calculation of dynamics of antiparticle cooling and annihilating in atomic gases. Developed for positron cooling and annihilation in atomic gases, but easily modifiable and applicable to other binary elastic-collision cooling processes governed by quantum-mechanical cross sections.Solution method: Monte Carlo simulation.Restrictions: Elastic scattering and annihilation only: positron energies must be below the positronium-formation threshold. It is a single particle program, i.e., positron–positron interactions are not included and binary collisions with the gas atoms are assumed.