1. NAME AND TITLE

AIRDIF: A Two-Dimensional Atmospheric Radiation Diffusion Code.

2. CONTRIBUTOR

U.S. Air Force Weapons Laboratory, Kirtland Air Force Base, New Mexico.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; CDC 6600/7600.

4. NATURE OF PROBLEM SOLVED

AIRDIF computes free field radiation environments from atmospheric nuclear detonations. It may be run in either homogeneous air or 2-D variable-density air. In addition to environments, AIRDIF can also compute K-Factors (ratio of 2-D to 1-D doses) for a particular source, dose response function, and at a number of mass ranges.

5. METHOD OF SOLUTION

AIRDIF employs a special form of diffusion theory which separates collided and uncollided multigroup fluences. An analytical first-collided source is used so that diffusion theory is only applied to the solution of the collided fluences. Solutions are thus obtained separately for the collided and uncollided fluences over each energy group throughout the region of interest. The total group fluences are then obtained by simple addition of the collided and uncollided particle fluences everywhere. Doses are computed by summing over all groups the product of the fluence and the dose response function in each group.

6. RESTRICTIONS OR LIMITATIONS

None noted.

7. TYPICAL RUNNING TIME

Execution times vary depending on the problem. The major factors causing variation in the time are the number of mesh points, the number of energy groups, and the rate of convergence of the iterative solution.

Typical times for execution on the CDC 7600 are approximately 60 seconds for 1500 mesh points and 58 energy groups. Execution on the CDC 6600 typically takes 4 to 5 times longer than on the CDC 7600.

8. COMPUTER HARDWARE REQUIREMENTS

AIRDIF is operable on the CDC 6600/7600 computers. The memory requirement for the CDC 6600 is approximately 200 K OCTAL. This provides adequate storage for 1500 mesh points and 61 particle energy groups. A maximum of 40 neutron groups and 21 gamma-ray groups can be used.

The CDC 7600 requires 220 K OCTAL LCM AND 33 K OCTAL SCM for 5000 mesh points and 61 particle energy groups.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran IV compiler is required.

10. REFERENCE

R. A. Shulstad and E. L. Wolf, "AIRDIF: A Two-Dimensional Atmospheric Radiation Diffusion Computer Code," AFWL-TR-77-29 (June 1977).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains the source codes.

12. DATE OF ABSTRACT

January 1982.