ANTICOOL: Simulating positron cooling and annihilation in atomic gases

The Fortran program ANTICOOL, developed to simulate positron cooling and annihilation in atomic gases 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 $\bar{Z}_{\rm eff}(t)$, 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.