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Manuscript Title: Codes for the combinatorial calculation of few quasiparticle state densities in spherical and deformed nuclei.
Authors: M. Herman, G. Reffo
Program title: ICAR AND CONV
Catalogue identifier: AAXS_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 47(1987)103
Programming language: Fortran.
Computer: IBM 3090/180.
Operating system: MVS/XA.
RAM: 348K words
Word size: 32
Peripherals: disc.
Keywords: Nuclear physics, Level density, Shell-model, Bcs model, Spin distribution, Preequilibrium model, Parity distribution, Multistep compound model, Theoretical methods.
Classification: 17.16, 17.19.

Nature of problem:
The codes calculate combinatorially state and, for spherical nuclei also, level densities characterized by a fixed number of quasiparticles in terms of the shell-model and the BCS theory. The spin and parity distributions are provided. The calculations can be done with or without pairing interaction taken into account and they can be restricted to bound states only to obtain the densities used in the statistical multi step compound model. An option for the calculation of the pairing strength parameter G from the experimental mass differences is provided. ICAR can be used also only for the determination of the BCS properties of the ground state and of the first excited state.

Solution method:
The code ICAR generate all possible configurations for selected number of quasiparticles (excitons) of a given nucleon type within a set of shell-model orbitals. For each configuration the energy, spin projection M and parity is determined. The configurations generated are sorted according to the excitation energy to obtain state densities. Results of ICAR for neutron and proton gas are convoluted by CONV code to obtain mixed configurations containing neutron and proton type of excitons. Performing this convolution no interaction between neutrons and protons is assumed.

Actual dimensions allow for the treatment of up to 5 particle type and 5 hole type excitons. Maximum number of the shell-model orbitals is restricted to 286 for photons and to 315 for neutrons. The considered energy range is limited to 40 MeV and 30 angular momentum units are taken into account.

Running time:
The calculation time of ICAR depends very strongly on the number of excitons considered and on the number of orbitals taken into account. Dependence on the mass number of the nucleus is less pronounced. Typical running times for 114 orbitals with pairing interaction accounted for are: 7 sec. for 2 excitons, 200 sec. for 3 excitons and around 3000 sec. for 4 excitons, when a spherical nucleus is considered. For deformed nuclei these values are to be increased approximately by a factor of 4. Neglecting the pairing interaction reduces the running time roughly by an order of magnitude. The calculation time of CONV is of the order of few seconds for all cases.