1. NAME AND TITLE

TRG-SGD: Calculation of Secondary Gamma-Ray Dose Rate from a Nuclear Weapon DetonationMonte Carlo Method.

2. CONTRIBUTORS

Biophysics Branch, Air Force Weapons Laboratory, Kirtland Air Force Base, New Mexico.

TRG, Incorporated, Melville New York.

The code was placed in the RSIC collection through the services of the DASA Data Center, GE-TEMPO, Santa Barbara, California. This early technology, still held by RSIC, is not generally recommended. It was used extensively in the 1960's; was distributed by RSIC to ten requestors during 1965-1970.

3. CODING LANGUAGE AND COMPUTER

FORTRAN; CDC 1604.

4. NATURE OF PROBLEM SOLVED

The TRG-SGD code calculates the time and space distribution of secondary gamma-ray dose and dose rate in the atmosphere and also in the ground near the surface of the earth. The neutron source is assumed to be given as leakage from a nuclear or thermonuclear device exploded in the air.

The effects of the blast and fireball on the transport of the neutrons and gamma rays are considered.

The following neutron reactions are considered: elastic scattering, inelastic scattering, radiative capture, and nonradiative capture. The (n,2n) reaction is treated as inelastic scattering by cross section modification. The prompt neutrons are from a degraded 14 MeV source due to fusion, a fission source, and a bomb thermal Maxwell-Boltzmann spectrum located at the burst point. The delayed neutrons are from fission source with a time-dependent volume distribution.

The only gamma-ray reactions considered are Compton scattering and absorption, the latter being the total of pair-production and photoelectric effect reactions.

5. METHOD OF SOLUTION

The Monte Carlo method is used to generate the neutron distribution, secondary gamma-ray source distribution, and secondary gamma-ray dose distribution. The effects of the air-ground interface, an inhomogeneous atmosphere, and the time-dependent hydrodynamics are taken into account. The type and yield of weapon and the detonation altitude determine the initial conditions. The geometric system is taken to be axially symmetric. In addition to statistical estimation of the gamma-ray source and dose distributions, various importance sampling techniques are used. These include Russian Roulette for low contribution particles and generalized quota sampling. In addition, all random variables are picked from a truncated exponential distribution. This procedure is controlled by input parameters.

6. RESTRICTIONS OR LIMITATIONS

The following list defines the largest number possible for the item named:

10 ground radial divisions

7 air layers

10 air radial divisions (each layer).

7. TYPICAL RUNNING TIME

No statistics are now available as to the typical running time.

8. COMPUTER HARDWARE REQUIREMENTS

The code is designed for a CDC 1604 Computer with a core memory of 32,000 words and 6+M tape units, where M (usually 2) is the number of tapes required by the system that are not available to the program.

9. COMPUTER SOFTWARE REQUIREMENTS

The code was written in FORTRAN 62 language to be compiled and executed under the CO-OP Monitor System. It may also be compiled in the FORTRAN 63 compiler.

The overlay feature is used, the program being divided into a main section and four overlays.

The main program's principal function is to call the four overlays into memory in their proper sequence. In addition, certain subroutines required by more than one overlay are included in the main section to eliminate the necessity of having them loaded separately with each overlay where they are needed.

10. REFERENCE

H. Steinberg and R. Aronson, "TRG-SGD, A Monte Carlo Program to Calculate Secondary Gamma Ray Dose from a Nuclear Weapon Detonation," WL-TDR-64-46, Vol. I and Vol II (July 1964).

11. CONTENTS OF CODE PACKAGE

The package contains the referenced document and one (1.2MB) DOS diskette on which is written in separate files: the source card decks and input and output for two sample problems.

12. DATE OF ABSTRACT

January 1966; updated July 1981; February 1984.

KEYWORDS: GAMMA RAY; ENVIRONMENTAL DOSE; MONTE CARLO; AIR TRANSPORT; WEAPONS RADIATION