CCC-0110: AIRTRANS, Time-Dependent, Energy Dependent 3-D Neutron Transport, Gamma Transport in Air by Monte-Carlo

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CCC-0110 AIRTRANS. (Abstract last modified 23-MAR-1988)

AIRTRANS, Time-Dependent, Energy Dependent 3-D Neutron Transport, Gamma Transport in Air by Monte-Carlo

Abstract Table of Contents:

1. NAME OR DESIGNATION OF PROGRAM - AIRTRANS.

2. COMPUTER FOR WHICH PROGRAM IS DESIGNED AND OTHER MACHINE VERSION PACKAGES AVAILABLE -

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Explanation of the status codes.

Program-name Package-ID Status AIRTRANS CCC-0110/01 Tested AIRTRANS CCC-0110/02 Obsolete AIRTRANS CCC-0110/03 Obsolete

Machines used: Package-ID Orig.Computer Test Computer CCC-0110/01 IBM 360 series IBM 360 series

3. NATURE OF PHYSICAL PROBLEM SOLVED - The function of the AIRTRANS system is to calculate by Monte Carlo methods the radiation field produced by neutron and/or gamma-ray sources which are located in the atmosphere. The radiation field is expressed as the time - and energy-dependent flux at a maximum of 50 point detectors in the atmosphere. The system calculates uncollided fluxes analytically and collided fluxes by the "once-more collided" flux-at-a-point technique. Energy-dependent response functions can be applied to the fluxes to obtain desired flux functionals, such as doses, at the detector point. AIRTRANS also can be employed to generate sources of secondary gamma radiation.

4. METHOD OF SOLUTION - Neutron interactions treated in the calculational scheme include elastic (isotropic and anisotropic) scattering, inelastic (discrete level and continuum) scattering, and absorption. Charged particle reactions, e.g, (n,p) are treated as absorptions. A built-in kernel option can be employed to take neutrons from the 150 kev to thermal energy, thus eliminating the need for particle tracking in this energy range. Another option used in conjunction with the neutron transport problem creates an "interaction tape" which describes all the collision events that can lead to the production of secondary gamma-rays. This interaction tape subsequently can be used to generate a source of secondary gamma rays.
The gamma-ray interactions considered include Compton scattering, pair production, and the photoelectric effect; the latter two processes are treated as absorption events.
Incorporated in the system is an option to use a simple importance sampling technique for detectors that are many mean free paths from the source. In essence, particles which fly far from the source are split into fragments, the degree of fragmentation being proportional to the penetration distance from the source. Each fragment is tracked separately, thus increasing the percentage of computer time spent following particles at the deep penetrations. Each fragment is assigned a "weight" which is inversely proportional to the degree of fragmentation suffered by original source particle.
All estimates of flux contributions by such a fragment are then multiplied by its assigned weight.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM -
ND = number of detectors less than or equal to 50*
NE = number of energy bins less than or equal to 50*
NT = number of time bins less than or equal to 50*
*subject to 3 ND x NE x NT + 2 NT x NE less than or equal to 1500- ited, where ited = 1464 for neutrons and 1054 for gammas.

6. TYPICAL RUNNING TIME - Estimated running time of the sample problem on the CDC 1604: AIRSCA, 3 minutes; DATORG, 3 minutes. Sample problem does not use VANGEN or ASP. Typical running time on the UNIVAC 1108 varies from 1/4 to 1/2 sec/history/detector.

7. UNUSUAL FEATURES OF THE PROGRAM -

9. STATUS
CCC-0110/01: 01-MAR-1979 Tested at NEADB
CCC-0110/02: 25-MAY-2001 Obsolete
CCC-0110/03: 23-MAR-1988 Obsolete

10. REFERENCES  -
- G.L. Case:
  Utilization Manual AIRTRANS
  LMSC-5234 (February 1968).
CCC-0110/01:
- M.O. Cohen:
  "AIRTRANS - A Time-Dependent Monte Carlo System for Radiation
   Transport in a Variable Density Atmosphere and the Ground"
  UNC-5179 (June 1967).

11. MACHINE REQUIREMENTS - The programme was originally designed for the CDC 1604 using standard I-O and a maximum of 4 tape units. It was converted for use on the UNIVAC 1108 by Lockheed Missile and Space Company.

12. PROGRAMMING LANGUAGE(S) USED -
CCC-0110/01: FORTRAN-IV

13. OPERATING SYSTEM OR MONITOR UNDER WHICH PROGRAM IS EXECUTED -

14. ANY OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS -

15. NAME AND ESTABLISHMENT OF AUTHOR -
United Nuclear Corporation
Elmsford, New York, U. S. A.
Lockheed Missile and Space Company Sunnyvale, California, U. S. A.

17. CATEGORIES -

- G. Radiological Safety, Hazard and Accident Analysis

Keywords: ABSORPTION, COLLISIONS, DOSES, ELASTIC SCATTERING, GAMMA RADIATION, INELASTIC SCATTERING, MONTE CARLO METHOD, NEUTRON TRANSPORT THEORY, RADIATION EFFECTS, SECONDARY EMISSION, TIME DEPENDENCE