1. NAME AND TITLE

HAM: Monte Carlo Multigroup Neutron and Photon High Altitude Transport Code System.

HAM (High Altitude MORSE) is the result of incorporating a continuous model of the air density variation at high altitudes into the MORSE Code package (CCC-127).

2. CONTRIBUTORS

Science Applications, Inc., La Jolla, California.

U.S. Army Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; UNIVAC 1108.

4. NATURE OF PROBLEM SOLVED

HAM is an extension of the MORSE Monte Carlo code system adapted for calculating neutron, secondary photon, and prompt photon fluxes from high altitude sources. All MORSE capabilities, to include time, angular, and energy dependent fluxes, and dose responses for forward and adjoint coupled transport, are retained.

Several special functions and subroutines were incorporated into the code to calculate curved earth mass penetration (PMASS), atmospheric density (RHOS), boundary scan (SEARCH), and curved earth collision site (SVAL).

5. METHOD OF SOLUTION

Monte Carlo methods are used to solve the transport equations as discussed in descriptive literature available on MORSE. In addition, variation in air density is treated as continuous for problems involving the non-homogeneous atmosphere. An amount of air mass penetrated from one collision site to the next is always computed.

The atmospheric model contains a curved earth treatment for high altitudes and long flight paths where significant differences exist in mass penetration between flat earth and curved earth calculations. Geometry routines treat the curved earth variation of air density in an analytical fashion rather than utilizing a conventional brute force approach of incorporating many constant density shells.

An analytical determination of particle position reduces time-consuming calculations of particle interactions with geometrical boundaries.

Problems are specified in terms of an earth-centered coordinate system with radial boundaries extending from earth surface upward, and angular boundaries displaced from a symmetry axis extending from earth center through the source.

Standard MORSE multigroup cross sections for air are used.

6. RESTRICTIONS OR LIMITATIONS

None noted. The code reverts to the conventional MORSE upon setting an input parameter.

7. TYPICAL RUNNING TIME

No study has been made by RSIC of typical running times for HAM.

8. COMPUTER HARDWARE REQUIREMENTS

HAM is operable on the UNIVAC 1108 computer and requires approximately 60 K decimal words. It may be run on the CDC or IBM machines with minimal modification. System clock is sampled. Standard system I/O hardware is adequate.

9. COMPUTER SOFTWARE REQUIREMENTS

A FORTRAN IV compiler is required. Clock routines are in combined Assembly and FORTRAN languages; other routines require standard computer software support.

10. REFERENCES

a. Included in package:

D. A. Sargis and W. A. Woolson, "HAM, A Version of the MORSE Code for High Altitude Transport," BRL-CR-228 (SAI-74-646-LJ) (May 1975).

b. Background information:

E. A. Straker, P. N. Stevens, D. C. Irving, and V. R. Cain, "The MORSE Code - A Multigroup Neutron and Gamma-Ray Monte Carlo Transport Code," ORNL-4585 (September 1970).

M. B. Emmett, "The MORSE Monte Carlo Radiation Transport Code System," ORNL-4972 (February 1975).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document (10.a) and one (1.2MB) DOS diskette which contains the source code and sample problem input and output.

12. DATE OF ABSTRACT

October 1978; revised March 1982, January 1983, January 1985.