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Manuscript Title: A C code for combining a Langevin fission dynamics of hot nuclei with a statistical model including evaporation of light particles and giant dipole gamma-quanta.
Authors: I. Gontchar, L.A. Litnevsky, P. Frobrich
Program title: DESCEND
Catalogue identifier: ADGX_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 107(1997)223
Programming language: C.
Computer: PC.
Operating system: MS-DOS, UNIX.
RAM: 8M words
Keywords: Nuclear physics, Preequilibrium decay, Nuclear fission, Langevin simulation, Statistical model, Nuclear friction.
Classification: 17.12.

Nature of problem:
The code calculates distributions of observables characterizing the deexcitation of highly excited and rotating atomic nuclei by fission and light particle and giant dipole gamma evaporation. Averages, variances and correlations of some observables are also calculated. The most important of the output parameters are: fission (respectively survival) probabilities, pre-scission neutron and charged-particle multiplicities and spectra, pre-scission gamma multiplicities and spectra, average energies of these particles, scission lifetime distributions, and excitation energies at scission. The code provides the possibility to investigate the influence of different nuclear friction form factors on the observable quantities.

Solution method:
The dynamical evolution of the compound nucleus is simulated numerically by means of a one-dimensional overdamped Langevin equation until after a certain delay time td a stationary regime is reached. Afterwards the decay is described by an adequately modified statistical model. An algorithm for light-particle evaporation (neutrons, protons, deuterons, alpha-particles, gamma-quanta) is coupled to the fission mode by a Monte Carlo procedure thus allowing for emission in discrete steps. Observables are calculated by sampling the corresponding events.

Running time:
The running time is defined mostly by the number of necessary trajectories and by the projectile energy. It also depends on the observable the user is interested in. The shortest time during which a meaningful result may be obtained for the fission probability and pre-scission neutron multiplicity is about 2 minutes (on a Pentium processor). If the interesting events are rare ones like giant dipole gamma-quantum emission, the running time can increase by 2 orders of magnitude.