1. NAME AND TITLE

CASIM: Monte Carlo Simulation of Transport of Hadron Cascades in Bulk Matter.

2. CONTRIBUTOR

Fermi National Accelerator Laboratory, Batavia, Illinois.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 370.

4. NATURE OF PROBLEM SOLVED

From the particle production model (in the form of a set of inclusive distributions) and a few other inputs (range-momentum relationship, inelastic interaction lengths, etc.) plus a geometry subroutine (generally supplied by the user) CASIM computes star densities (i.e., nuclear interaction densities) as a function of location and particle type throughout the target. From these star densities, estimates of a number of quantities of radiobiological interest, e.g., dose equivalent due to direct irradiation, CASIM also calculates momentum spectra of interacting particles, also as a function of location in the shield and of particle type. The particles considered are: protons, neutrons, and charged pions. A further option is the calculation of energy deposited by the cascade. This quantity is a useful measure of target heating and can be related to light output of a plastic scintillator embedded in the target (ionization calorimeters).

As presently designed, CASIM only yields the average energy deposited as a function of location.

Alternative to the energy deposition option is an option which calculates a relative error of the average (total) number of stars as a function of location.

CASIM contains a condensed version of SPUKJ (developed by J. Ranft at CERN, Geneva, Switzerland) for the calculation of inclusive production cross sections of protons and pions due to protons interacting with nuclei.

5. METHOD OF SOLUTION

CASIM is a Monte Carlo code system which studies the average development of internuclear cascades when high energy particles are incident on large targets (shields) of arbitrary geometry and composition. It is aimed at problems for incident particles in the range 20-1000 GeV/c and does not study the transport of low energy particles (0.3 GeV/c). In contrast to similar code systems, CASIM uses directly inclusive distributions, i.e., particle yields as a function of angle and momentum (or other equivalent variables) from inelastic particle-nucleus interactions. The use of weighting techniques avoids difficulties of random selection encountered in sampling complicated distributions and allows the user to introduce bias in the sampling.

To save computing time, coding and storage all particles of an entire generation are represented by two weighted Monte Carlo particles. One is chosen to propagate the cascade to the next generation, the other to record the contribution of the present generation.

6. RESTRICTIONS OR LIMITATIONS

Momenta of particles included in the calculation should not be less than 0.1 GeV/C. A low momentum cut-off above 0.3 GeV/c is recommended.

7. TYPICAL RUNNING TIME

1.5 minutes to prime the Monte Carlo plus about 1.0 minute per 5000 ``stars.'' Actual running time depends strongly on the problem and on statistical accuracy desired. Typically this is in the range of 20,000 to 200,000 stars.

8. COMPUTER HARDWARE REQUIREMENTS

CASIM was designed to run on an IBM 370/195 computer with approximately 400 K storage.

9. COMPUTER SOFTWARE REQUIREMENTS

A FORTRAN IV compiler is required.

10. REFERENCE

A. Van Ginneken, "CASIM: Program to Simulate Transport of Hadronic Cascades in Bulk Matter," FN-272, (January 1975).

11. CONTENTS OF CODE PACKAGE

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

12. DATE OF ABSTRACT

August 1979; revised March 1982, updated January 1983, reviewed January 1985.