RSICC CODE PACKAGE PSR-226
1. NAME AND TITLE
PRECO-2006: Exciton Model Preequilibrium Nuclear Reaction Code with Direct Reactions.
2. CONTRIBUTOR
Triangle Universities Nuclear Laboratory, Duke University, Durham, North Carolina.
3. CODING LANGUAGE AND COMPUTER
Fortran 77; PC and IBM RS/6000 (P00226MNYCP02).
4. NATURE OF PROBLEM SOLVED
preco-2006 is a two-component exciton model code for the calculation of double differential cross sections of light particle nuclear reactions. PRECO calculates the emission of light particles (A = 1 to 4) from nuclear reactions induced by light particles on a wide variety of target nuclei. Their distribution in both energy and angle is calculated. Since it currently only considers the emission of up to two particles in any given reaction, it is most useful for incident energies of 14 to 30 MeV when used as a stand-alone code. However, the preequilibrium calculations are valid up to at least around 100 MeV, and these can be used as input for more complete evaporation calculations, such as are performed in a Hauser-Feshbach model code. Finally, the production cross sections for specific product nuclides can be obtained
5. METHOD OF SOLUTION
The code uses simple, relatively phenomenological statistical models. The main calculations employ a closed form version of the exciton preequilibrium model to follow the evolution of the fused target-plus-projectile composite nucleus as the energy brought in by the incident particle gets gradually redistributed due to the creation of new particle and hole degrees of freedom. Once statistical equilibrium is reached, traditional compound nucleus evaporation calculations are used. Additional subroutines calculate direct reaction mechanisms whose contributions are not included in the main preequilibrium calculations. These mechanisms include nucleon transfer processes, knockout, and inelastic scattering involving complex particles and collective state excitation. Shell structure, pairing interactions and isospin conservation are all considered in approximate ways in the two-component particle-hole state densities used in the preequilibrium calculations. Emission of a second nucleon at either the preequilibrium or equilibrium phase of the reaction is allowed following neutron or proton emission.
6. RESTRICTIONS OR LIMITATIONS
The restriction to only two emitted particles simply means that the evaporation peak in the spectrum may be underestimated for incident energies above about 30 MeV. Because the approach is statistical, detailed information on individual nuclear states is not considered except for a few strong collective states, and even there, only the smooth trends of their angular distributions are given. In addition the contributions from neutrons emitted during fission are not currently calculated. The preequilibrium parts of PRECO can be (and earlier versions have been) used in larger Hauser-Feshbach model, thus expanding its usefulness. Additional work needs to be done for reactions induced by complex projectiles (deuterons, tritons, He-3 and alpha-particles), since projectile breakup reactions, which can be quite important, are not yet included in the code.
7. TYPICAL RUNNING TIME
The running time depends on the size of the nucleus (heavier nuclei take longer), the number of emission energies being calculated (i.e. the fineness of the emission energy mesh), and somewhat on the incident energy. Calculations with only one emitted particle also run very much faster than those where secondary emission is also calculated. Typical running times on a 233 MHz PC are less than 1 second to around 10 seconds for a single problem. On a 1.86 GHz PC, the longest reactions typically run in about 1-1.5 seconds.
8. COMPUTER HARDWARE REQUIREMENTS
PRECO-2006 was developed on an IBM / Lenovo Thinkpad T43 running under Windows XP Professional. It also runs on Sun and IBM workstations.
9. COMPUTER SOFTWARE REQUIREMENTS
The Microsoft FORTRAN compiler version 5.0 (copyright 1987‑1989) was used to build the executable included in the package. This executable was tested at RSICC in a DOS window of WindowsXP and Windows Vista. The code was also tested at RSICC on:
Pentium PC running Windows XP and with Lahey-Fujitsu lf95 v7.1
Pentium PC running Windows VISTA with Compaq Digital Visual Fortran 6.6C
PC running Red Hat Enterprise Linux 4 and Ubuntu 7.04 with 32-bit g77 3.4.6
IBM RS/6000 running AIX 5.1 with IBM XL Fortran for AIX Version 8.01.
10. REFERENCE
a. included in documentation:
Constance Kalbach Walker, “Users Manual for PRECO-2006: Exciton Model Preequilibrium Nuclear Reaction Code with Direct Reactions,” Triangle Universities Nuclear Laboratory report (unnumbered) (February 2007).
b. background reference:
C. K. Walker, “Users Manual for PRECO-2000 Exciton Model Preequilibrium Code with Direct Reactions,” Triangle Universities Nuclear Laboratory Report (unnumbered) (March 2001).
C. Kalbach, “PRECO-D2: Program for Calculating Pre-equilibrium and Direct Reaction Double Differential Cross Sections,” LA-10248-MS (February 1985).
11. CONTENTS OF CODE PACKAGE
Included are the referenced document in 10.a, the source code, Windows executable and sample problem. The package is distributed on a CD in both WinZIP and Unix tar files.
12. DATE OF ABSTRACT
June 1986, revised June 2001, revised June 2007.
KEYWORDS: CROSS SECTIONS; ENERGY SPECTRA; NUCLEAR MODELS