1. NAME AND TITLE

NUGAM 2&3: Monte Carlo Prediction of Photon Transport Distributions.

2. CONTRIBUTORS

NUS Corporation, Rockville, Maryland.

NASA Goddard Space Flight Center, Greenbelt, Maryland.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

NUGAM2 predicts the forward and backward angular-energy distributions of gamma-ray photons and fluorescent radiation emerging from finite transport media of single or laminar composition. NUGAM3 predicts the pulse height response of inorganic scintillation crystals exposed to gamma-ray photon radiation. This crystal model may be encased in a cladding material and mounted on a hypothetical photomultiplier.

5. METHOD OF SOLUTION

NUGAM2 and NUGAM3 employ the Monte Carlo technique of following and categorizing a large number of photons from "birth to death." They use random number and probability theory combined with known interaction distributions to determine source and collision site spatial locations, as well as trajectory, energy and direction throughout each history.

NUGAM2 handles Monte Carlo gamma-ray photon transport in finite laminar media. NUGAM3 does Monte Carlo prediction of the response of clad scintillation detectors exposed to gamma-ray photons in the energy range to 4.5 MeV.

6. RESTRICTIONS OR LIMITATIONS

For NUGAM2, the number of transport material laminations is limited to nine or less.

7. TYPICAL RUNNING TIME

In the IBM 360/91 computer, running times are primarily a function of transport medium size and atomic number, and source photon energy. For example, NUGAM2 executes at ~ 4500 photon histories per minute for an iron transport medium when E = 1.0 MeV, length of the cylindrical medium = 32 and radius = 52. NUGAM3 executes at ~ 8,000 photon histories per minute for E = 0.662 or 2.754 MeV and 3] x 3] NaI(Tl) clad detector The times required for test runs were:

NUGAM2: greater than 5.50 minutes on the IBM 360/91 computer;

NUGAM3: approximately 1.5 minutes on the IBM 360/75 computer.

8. COMPUTER HARDWARE REQUIREMENTS

NUGAM 2&3 are operable on the IBM 360/370 computers. On an IBM 360/91, NUGAM2 requires 330 K bytes of storage and NUGAM3 requires 180 K bytes.

9. COMPUTER SOFTWARE REQUIREMENTS

A FORTRAN IV compiler is required.

10. REFERENCE

J. J. Steyn, R. Huang, and H. Firstenberg, "Final Report for Modification of Codes Nualgam and Bremrad," NUS-786/1, Volumes 1-3 (May 1971).

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 and output.

12. DATE OF ABSTRACT

May 1975.

KEYWORDS: MONTE CARLO; GAMMA-RAY; CYLINDRICAL GEOMETRY; SLAB; SCINTILLATION DETECTOR; SODIUM IODIDE