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Manuscript Title: Monte Carlo simulation of fluctuations of the ionization losses of heavy charged particles.
Authors: A.D. Bukin, N.A. Grozina
Program title: FLION
Catalogue identifier: ACPN_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 78(1994)287
Programming language: Fortran.
Computer: IBM-370.
Operating system: VM/CMS, VMS.
RAM: 9K words
Word size: 32
Keywords: Particle physics, Elementary, Detector design, Monte carlo simulation, Ionization losses, Interaction of Particles with matter, Particle detectors, Vavilov, Landau.
Classification: 11.7.

Nature of problem:
Detailed Monte Carlo simulation of interaction of particles with a detector is necessary both for preparing an experiment (optimization of the detector, choosing cuts etc.) and for the processing of experimental results (calculation of detection efficiencies). Ionization losses of charged particles are an essential part of this interaction. In a realistic simulation not only the average ionization losses but also their fluctuations should be taken into account.

Solution method:
Ionization loss fluctuations are described by the modified Vavilov distribution [1]. The inverse function to the integrated probability distribution is approximated using splines that allows the fast calculation.

The distance travelled by the particle should not be too large so that the energy loss must be much smaller than the particle kinetic energy. On the other hand, this distance should not be too small (especially in gases) so that the number of collisions with atoms with the energy transfer of order of the ionization energy must be much larger than unity.

Running time:
About 1 msec per call on the VAX-3600 computer.

[1] P.V. Vavilov. JETP 32(1957)920.