1. NAME AND TITLE
PICA: Monte Carlo Medium-Energy Photon-Induced Intranuclear Cascade Analysis Code System.
AUXILIARY ROUTINES
CON: Data Conversion (BCD to binary) Code.
PIC: Cascade Data Generator.
MECCAN: Interaction Data Analysis Code.
EVAP: Evaporation Data Generator.
NUC: Nuclear Configuration Code.
FLRAN, FLOTR, FLTRN: Random Number Generators.
DATA LIBRARIES
CS: Cross Sections and Nuclear Configuration Data.
ET: Evaporation Tables for EVAP.
2. CONTRIBUTOR
Oak Ridge National Laboratory, Oak Ridge, Tennessee.
3. CODING LANGUAGE AND COMPUTER
FORTRAN IV; IBM 360/75/91 (C00160I036000)
Fortran 77; VAX (C00160D0VAX00)
Random number generators are written in Assembly language for the IBM 360.
4. NATURE OF PROBLEM SOLVED
PIC calculates the results of nuclear reactions caused by the collision of medium-energy photons with nuclei. The photon energy range in which the calculations are applicable is 30 < E < 400 MeV. All target nuclei with mass numbers > 4 are possible. The program PIC can accommodate incident monoenergetic photons as well as thin-target bremsstrahlung spectra, thin-target bremsstrahlung difference spectra and thick-target bremsstrahlung spectra. For the last type of spectra the user must furnish the photon spectral data. PIC writes a history tape containing data on the properties of the particles (protons, neutrons, or pions) escaping from the nucleus. The data consists of the types of escaping particles and their energies and angles of emission. MECCAN utilizes the data on the PIC history tape to calculate cross sections such as the nonelastic cross section or the doubly differential cross section for energy-angle correlated distributions. EVAP then carries the nuclear reaction through an additional phase, that of evaporation, and calculates the energy spectra of particles (protons, neutrons, deuterons, tritons, 3He, and alpha particles) "boiled off" from the nucleus after the cascade has stopped, evaporation particle multiplicities, and evaporation residual nuclei (radio-chemical) cross sections.
5. METHOD OF SOLUTION
The interaction of high-energy photons with nuclei is described by using the intranuclear-cascade and evaporation models. Monte Carlo methods are employed to provide a detailed description of each interaction. The initial interaction of the photon with the nucleus is obtained from the quasi-deuteron model of Levinger, that is, photon absorption by a neutron-proton pair moving within the nucleus or from one of the four pion-nucleon states formed in the photon-nucleon interaction. The effect of secondary nucleon-nucleus and/or pion-nucleus interactions following the photon absorption is accounted for by utilizing the intranuclear-cascade concept of high-energy particle-nucleus reactions. Each particle involved in a collision is traced through the nucleus using the appropriate particle-particle cross sections until the particle escapes from the nucleus or is captured by the nucleus. In all parts of the calculation, the Fermi momentum of the struck particle, the exclusion principle, and the nonuniform density distribution are taken into account. Following the cascade phase, the nucleus is usually in a state of high excitation. This excitation energy can be dissipated through particle emission. This de-excitation is handled by the evaporation model.
NUC creates modified nuclear configuration data input for PIC. In PIC three nuclear regions are used to approximate a continuous nucleon-density distribution in the nucleus, and the radii of these regions can be changed by using NUC. PIC uses an exact sampling technique to determine the collision site and the types of particles in the reaction.
6. RESTRICTIONS OR LIMITATIONS
The range of validity of PIC is from 30 to 400 MeV for the energy of the incident photon.
7. TYPICAL RUNNING TIMES
The approximate machine time to obtain reasonable statistical accuracy is 30 to 60 minutes on the IBM 360/75 computer.
Estimated running times of the packaged sample problem: CON, one minute; PIC, 2 minutes; MECCAN, one second; EVAP, 5 seconds; and NUC, one second.
The run time for PIC on a VAX 6000-420 using 40000 incident particles is 34 seconds.
8. COMPUTER HARDWARE REQUIREMENTS
The codes were designed for the IBM 360/75/91 computer configuration, requiring a maximum of 3 tape units or direct access devices in addition to I-O. Storage (GO STEP) required: CON, 15K; PIC, 300K; MECCAN, 40K; EVAP, 250K; and NUC, 160K. In February 1994 the VAX package was released. It is a conversion of the February 1971 IBM version.
9. COMPUTER SOFTWARE REQUIREMENTS
The codes packaged are operable on the IBM 360/75/91 Operating System using OS-360 Level 18 FORTRAN H Compiler and on DEC VAX computers using VMS and the VAX Fortran compiler.
10. REFERENCES
T. A. Gabriel, M. P. Guthrie, and O. W. Hermann, "Instructions for the Operation of the Program Package PICA, An Intranuclear-Cascade Calculation for High-Energy (30 to 400 MeV) Photon-Induced Nuclear Reactions," ORNL-4687 (September 1971).
T. A. Gabriel and R. G. Alsmiller, Jr., "Photonuclear Disintegration at High (< 350 MeV) Energies," (Thesis), ORNL-TM-2481 (February 1969).
H. W. Bertini, "Intranuclear Cascade Calculation of the Secondary Nucleon Spectra from Nucleon-Nucleus Interactions in the Energy Range 340 to 2900 MeV and Comparisons with Experiment," Phys. Rev. 188, 1711-1730 (1969).
11. CONTENTS OF CODE PACKAGE
Included are the referenced documents and one (1.2MB) DOS diskette which contains the source codes, data libraries, and sample problem input and output.
12. DATE OF ABSTRACT
June 1972; revised December 1984; revised January 1994.
KEYWORD: INTRANUCLEAR CASCADE