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Manuscript Title: Subroutines for the evaluation of cross sections of one-photon radiative processes occuring in fast-electron H-atom collisions.
Authors: A. Dubois, A. Maquet
Program title: BREMSS
Catalogue identifier: ABTF_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 60(1990)271
Programming language: Fortran.
Computer: MACINTOSH II.
Operating system: DK1-6.0.2.
RAM: 10K words
Word size: 8
Peripherals: disc.
Keywords: Atomic physics, Photon, Atom-electron, Collision, Bremsstrahlung radiation, Double differential Cross section, Adaptive gauss-legendre Quadrature.
Classification: 2.5.

Nature of problem:
During a collision event, the coupling of the electron-atom system with the empty modes of the electromagnetic field can lead to the spontaneous emission of bremsstrahlung radiation. The related transistion amplitude is, apart from a multiplicative factor, identical to the free-free transition one. Using the very compact form of this latter, the present routine evaluates the twofold differential bremsstrahlung cross section, i.e. the integration of the transition amplitude over all propagation directions of the outgoing electron.

Solution method:
The numerical integration presents some difficulties due to localized sharp peaks in the integrand. To deal with such problems, we have written a very efficient adaptive Gauss-Legendre quadrature routine.

Restrictions:
Low projectile energies and emission of photons with frequency matching atomic excitation frequencies are prohibited.

Unusual features:
The adaptive quadrature routine requires full recursivity qualities from the Fortran compiler.

Running time:
The time required to evaluate a cross section is typically one minute.