PSR-0226 PRECO.

PRECO-D2.

PRECO-2000.

The code PRECO-D2 uses the exciton model for preequilibrium nuclear reactions to describe the emission of particles with mass numbers of 1 to 4 from an equilibrating composite nucleus. A distinction is made between open  and closed configurations in this system and between the multi-step  direct (MSD) and multi-step compound (MSC) components of the preequilibrium cross section. Additional MSD components are calculated semi-empirically to account for direct nucleon transfer reactions and direct knockout processes involving cluster degrees of freedom. Evaporation from the equilibrated composite nucleus is included in the full MSC cross section. Output of energy differential and double differential cross sections is provided for  the first particle emitted from the composite system. Multiple particle emission is not considered. This report describes the reaction models used in writing PRECO-D2 and explains the organization and utilization of the code.

PRECO-2000, also known as PRECOM (M for Millenium), 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; but the preequilibrium calculations are valid up to at least around 100 MeV.

The code uses simple, relatively phenomenological statistical models. The main calculations involve a closed form version of the exciton preequilibrium model to follow the evolution of the fused target projectile composite nucleus as the energy brought in by the incident particle gets gradually redistributed by the creation of new particle-hole pairs. 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.

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.

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.

- C. Kalbach:
  PRECO-D2: Program for Calculating Preequilibrium and Direct
  Reaction Double Differential Cross Sections.
  LA-10248-MS  (February 1985)

- C. Kalbach,
  "PRECO-D2: Program for Calculating Pre-equilibrium and Direct
  Reaction Double Differential Cross Sections,"
  LA-10248-MS (February 1985).
- C. K. Walker,
"Users Manual for PRECO-2000 Exciton Model Preequilibrium Code with Direct
Reactions
Triangle Universities Nuclear Laboratory Report (unnumbered) (March 2001).

PRECO-2000 was developed on PC. It also runs on Sun and IBM workstations.

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 WindowsNT. The code was also tested at RSICC on PC with Lahey F95 and Digital Visual Fortran 6.0, on IBM RS/6000 under AIX 4.3.3 with XL Fortran 7.1, and on Sun under Solaris 2.6 with f77 5.0.

          C. Kalbach
          Department of Physics
          Duke Univ.
          Durham, NC27706

Contributed by:
                    Radiation Safety Information
                    Computational Center
                    Oak Ridge National Laboratory
                    Oak Ridge, Tennessee, U. S. A.

Developed by:       Triangle Universities Nuclear Laboratory,
                    Duke University, Durham, North Carolina
                    U.S.A.

precom.dat Data file
precom.exe Microsoft-compiled exe dir for PC
precom.for  Source code
precom2.for Source code
precom3.for Source code
precom4.for Source code
precom_pc.out    PC output
precom_rsk6.out  IBM RS/6000 output
precom_sun.out   Sun output
preco_doc.pdf    User Manual
Readme.txt       Installation info

File name	File description	Records
PSR0226_01.001	Information file	46
PSR0226_01.002	JCL and control information	16
PSR0226_01.003	PRECO-D2 FORTRAN source	1900
PSR0226_01.004	Sample problem input	78
PSR0226_01.005	Sample problem output	1112
PSR0226_01.006	Logfile sample problem	63