1. NAME AND TITLE

GASS: Monte Carlo Calculation of Self Shielding by Encapsulated Gamma-Ray Sources.

This code package originated in Office of Civil Defense programs in 1966; is retained by RSIC to preserve the technology.

2. CONTRIBUTOR

University of Illinois, Civil Engineering and Nuclear Engineering Program, Urbana, Illinois.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 7090 and 7094.

4. NATURE OF PROBLEM SOLVED

GASS was designed to calculate the energy and angular distributions of photons emitted from a cylindrical or spherical encapsulated source.

5. METHOD OF SOLUTION

GASS represents an approximate solution by Monte Carlo methods to the steady state transport equation.

A time-saving procedure utilizing a "do-nothing" cross section allows ray tracing to proceed without many cross section look-ups and partial path length calculations. A choice is then made where the collision occurs between scattering, absorption, or the straight-ahead "do-nothing" reaction.

6. RESTRICTIONS OR LIMITATIONS

There are no known restrictions implied by storage allocation.

7. TYPICAL RUNNING TIME

Processing of 20,000 histories in the sample problem required 3 minutes on the IBM 7090 and 1.3 minutes on the 7094.

8. COMPUTER HARDWARE REQUIREMENTS

The code was designed for the 32 K IBM 7094 computer with 3 tape units.

9. COMPUTER SOFTWARE REQUIREMENTS

The code may be compiled and executed on the IBM FORTRAN IV IBJOB Monitor and other compatible systems. Standard I-O and systems tape assignments are made.

10. REFERENCE

K. Preiss, "Monte Carlo Calculation of Self Shielding by Encapsulated Gamma Ray Sources," UI-NRSS-3 (August 1966).

11. CONTENTS OF CODE PACKAGE

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

12. DATE OF ABSTRACT

January 1968; updated July 1981, February 1985.