NESC0171 NEARREX.

1. NAME OR DESIGNATION OF PROGRAM:  NEARREX.

3. NATURE OF PHYSICAL PROBLEM SOLVED

NEARREX computes neutron- induced, average fluctuation (or compound nucleus) cross sections. Provision is made for the computation of compound elastic and inelastic neutron cross sections, radiative capture and fission cross sections, as well as other processes, such as proton emission. It can also be used to compute proton-induced average cross sections.

4. METHOD OF SOLUTION

At each incident neutron energy E, a neutron partial wave channel is specified by its orbital angular-momentum quantum number, L, by the total neutron angular momentum, jay= L+(or-)1/2, by the total angular momentum, J, and by the residual state of the target nucleus. These residual states can be any one of the ground or excited states of the target nucleus, for which excitation energies, spins, and parities (Pi) must be specified. The average resonance parameters for each of these neutron channels are  computed as a function of the compound transmission coefficients, specified as input. The latter will usually be obtained from an optical model calculation. The average resonance parameters for radiation channels are computed using various approximations. The parameter sigma can be given the values 2, 4, 6, 8, or 10. Setting sigma equals 0 or 12 results in F identically equal to 1, or F identically equal to 2J+1, respectively. The lumped resonance parameters for each J,Pi are assumed to be independent of the resonance indices.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

The statistical parameter, Q(alpha), must be specified to have the same value for all channels in this program. For This reason, it is in general only safe to specify q values between 0 and 1. Each neutron partial wave  is assumed to be distributed according to the chi-square distribution with one degree of freedom (Porter-Thomas).

6. TYPICAL RUNNING TIME

0.04NE(NMAX+1)(2LMAX+1) minutes for the IBM704. CDC3600 should be about 8 to 10 times faster for large problems. NE=number of incident neutron energies. NMAX=number of excited levels of target nucleus. LMAX=maximum L-value used for transmission coefficients.

7. UNUSUAL FEATURES OF THE PROGRAM

The input format for the elastic and inelastic T(alpha,comp) is the same as the format of the transmission coefficients that can be punched from the ABACUS2 optical mode code. However, the number of transmission coefficients  punched by ABACUS 2 will usually not coincide with the number required in the input of NEARREX.

8. RELATED AND AUXILIARY PROGRAMS

ABACUS2 produces transmission coefficients that can be used by NEARREX.

- P. A. Moldauer, C. A. Engelbrecht, and G. J. Duffy,
  NEARREX, A Computer Code for Nuclear Reaction Calculations,
  ANL-6978, December 1964.
- A. Prince, G. Reffo, E. Sartori:
  "Report on the International Nuclear Model Code Intercomparison,
   Spherical Optical and Statistical Model Study", October 1983
  NEANDC/INDC(NEA)4

11. HARDWARE REQUIREMENTS: MACHINE REQUIREMENTS

13. OPERATING SYSTEM OR MONITOR UNDER WHICH PROGRAM IS EXECUTED: SCOPE (CDC3600).

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

ANY OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

15. NAME AND ESTABLISHMENT OF AUTHOR

                 P. A. Moldauer, Reactor Physics Division
                 G. J. Duffy, Applied Mathematics Division
                 Argonne National Laboratory
                 9700 South Cass Avenue
                 Argonne, Illinois  60439

                 C. A. Engelbrecht
                 South African Atomic Energy Board
                 Private Bag 256
                 Pelindaba, Pretoria, South Africa

File name	File description	Records
NESC0171_02.001	SOURCE & DATA 360/65	1201
NESC0171_02.002	OUTPUT	83