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Manuscript Title: Monte Carlo simulation of photons in two-layered media for density gauges.
Authors: E.R. Christensen
Program title: MCS
Catalogue identifier: AAUK_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 7(1974)185
Programming language: Fortran.
Computer: IBM 370/165.
Operating system: HASP II.
RAM: 18K words
Word size: 32
Keywords: Nuclear physics, Photon scattering, Monte carlo method, Two-layered-medium, Axial symmetry, Principle of similitude.
Classification: 17.1.

Nature of problem:
Multiple photon scattering in a two-layered medium is considered. The photons are assumed to originate from a mono-energetic point source situated at an arbitary height over the medium. The relative number of backscattered photons, weighted with a detector efficiency spectrum, is calculated in consecutive radial intervals.

Solution method:
Photons are simulated by the Monte Carlo method. Stratified sampling is applied to the isotropically emitted source photons. The scattering is determined by iteration from Klein-Nishina cross section.

Restrictions:
A maximum of 12 elements, 19 energy groups, 16 radial-, and 18 depth intervals may be considered. The perpendicular to the plane medium, through the source, is an axis of symmetry, and thus only axial symmetrical problems can be solved.

Unusual features:
Responses in different radial intervals can by the principle of simili- tude be interpreted as responses in a given interval at different densities. This presupposes a source height of zero, a semi-finite medium and similiar radial intervals.

Running time:
Simulation of 90 000 photon histories takes about 3 min of central processor time.