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 Z eff , 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 Z eff ( 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 summary Program title: ANTICOOL Program Files doi: http://dx.doi.org/10.17632/kjstc6xskg.1 Licensing provisions: GPLv3 Programming language: Fortran 90 Nature 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.