RSIC COMPUTER CODE PSR-023

1. NAME AND TITLE

SPECTER: Calculation of Energy Distribution of Nuclear Reaction Products.

2. CONTRIBUTOR

Brown Engineering Company, Inc., Huntsville, Alabama.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; IBM 360/65/75/91.

4. NATURE OF PROBLEM SOLVED

SPECTER calculates the energy spectra of particles emerging from reactions of the types (y,n), (y,p), (y,alpha), (y,2n), (y,np), (y,pn), and (y,2p) where the incident particle y may be either n, p, or alpha. In addition, the code calculates the cross section for each of these reactions.

5. METHOD OF SOLUTION

SPECTER is an outgrowth of PSR-6/EDISN. Whereas EDISN is capable of handling only (n,n') and (n,2n) reactions, SPECTER can treat all the reactions specified above. SPECTER makes use of the Weisskopf-Ewing formula to calculate the energy distributions and reaction cross sections. The cross sections for compound-nucleus formation that are needed in evaluating this formula are calculated by the continuum theory of nuclear reactions. Data required as input are the bombarding energy, the masses of all nuclear species taking part in the reaction, and certain parameters that specify the level density of participating nuclei.

For completeness, a subroutine for calculating the nuclear level density has been included. This subroutine makes use of the commonly adopted level density formula

derived from the Fermi gas model. U is obtained by adjusting the excitation energy to account for the pairing energy. The user may wish to employ some other analytic expression for rho or a table of values. In this event, the subroutine may be suitably modified or replaced.

A table of cross sections for compound nucleus formation as a function of bombarding energy and target mass number is generated during the first run and written on magnetic tape for use in all subsequent runs. These cross sections are calculated by the continuum theory. Optionally, the user could perform a more sophisticated treatment by replacing this table with a similar one generated from optical model calculations.

6. RESTRICTIONS OR LIMITATIONS

Ideally, the code is suited to reactions which proceed through the formation of a compound nucleus (CN). In cases, however, in which the direct interaction mechanism (DI) is also operative, the code is useful in estimating the relative contribution from direct effects, provided the entire cross section for the process, sigma_CN+DI, be known, e.g., from experiment. In addition, it is required that the level structures for all residual nuclei be adequately described by continuous level densities.

7. TYPICAL RUNNING TIME

Running time is highly dependent upon the number of energy increments used in the numerical integrations. The maximum degree of accuracy is attained with 50 increments. In this case, a typical calculation on ⁵⁶Fe at 14 MeV which takes into consideration the reactions (n,n'), (n,2n), and (n,p) takes about three minutes on the IBM 7094 computer.

8. COMPUTER HARDWARE REQUIREMENTS

SPECTER is operable on the IBM 360/65/75/91 computer. 29 K of memory is required. However, with some sacrifice in accuracy, this requirement may be relaxed considerably by the reduction of certain array dimensions.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran H-level compiler is required. The Standard Monitor system is used.

10. REFERENCE

R. Snow and M. C. George, "A Computer Code for Calculating the Energy Distribution of Nuclear Reaction Products," SMSD-SSL-1100 (February 1970).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains the source code and data input and output.

12. DATE OF ABSTRACT

November 1972; revised November 1983.