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Manuscript Title: POSDIF: a program to compute positron diffusion and annihilation in rare gases.
Authors: R.I. Campeanu
Program title: POSDIF
Catalogue identifier: AAHN_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 25(1982)433
Programming language: Fortran.
Computer: IBM-360.
RAM: 26K words
Word size: 32
Keywords: Atomic physics, Experiment, Positron, Diffusion equation, Lifetime spectrum, Crank-nicolson method, Finite differences, Momentum transfer, Effective charge.
Classification: 2.3.

Nature of problem:
Calculates positron lifetime spectrum in a gas being given the gas pressure and temperature, the value of the external electric field strength and the fits to momentum dependence of the positron-atom momentum transfer cross section and of the effective charge number.

Solution method:
The parabolic equation, representing positron diffusion and annihilation in the gas, is solved using Crank-Nicholson method and other standard finite difference methods. At each timestep the velocity distribution is used to calculate the averaged effective charge number and the averaged positron momentum.

Running time:
About 300 s CPU time on the IBM-360.