NAME OR DESIGNATION OF PROGRAM, COMPUTER, NATURE OF PHYSICAL PROBLEM SOLVED, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, FEATURES, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM, OTHER RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES

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Program name | Package id | Status | Status date |
---|---|---|---|

AIRTRANS | CCC-0110/01 | Tested | 01-MAR-1979 |

Machines used:

Package ID | Orig. computer | Test computer |
---|---|---|

CCC-0110/01 | IBM 360 series | IBM 360 series |

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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.

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.

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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.

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.

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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.

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.

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CCC-0110/01, included references:

- 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).

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CCC-0110/01

File name | File description | Records |
---|---|---|

CCC0110_01.001 | INFORMATION | 6 |

CCC0110_01.002 | 81 PTS. NEUTRON CROSS SECTIONS (BCD) | 8307 |

CCC0110_01.003 | 81 PTS. GAMMA CROSS SECTIONS (BCD) | 2642 |

CCC0110_01.004 | DATORG --- SOURCE PROGRAM (F4,EBCDIC) | 365 |

CCC0110_01.005 | DATORG1 --- DD CARDS | 8 |

CCC0110_01.006 | DATORG1 --- SAMPLE PROB. INPUT DATA | 238 |

CCC0110_01.007 | DATORG1 --- SAMPLE PROB. PRINTED OUTPUT | 536 |

CCC0110_01.008 | DATORG2 --- DD CARDS | 8 |

CCC0110_01.009 | DATORG2 --- SAMPLE PROB. INPUT DATA | 238 |

CCC0110_01.010 | DATORG2 --- SAMPLE PROB. PRINTED OUTPUT | 415 |

CCC0110_01.011 | VANGEN --- SOURCE PROGRAM (F4,EBCDIC) | 365 |

CCC0110_01.012 | VANGEN --- DD CARDS | 5 |

CCC0110_01.013 | VANGEN --- SAMPLE PROB. INPUT DATA | 6 |

CCC0110_01.014 | VANGEN --- SAMPLE PROB. PRINTED OUTPUT | 608 |

CCC0110_01.015 | ASP --- SOURCE PROGRAM (F4,EBCDIC) | 615 |

CCC0110_01.016 | ASP --- DD CARDS | 8 |

CCC0110_01.017 | ASP --- SAMPLE PROB. INPUT DATA | 8 |

CCC0110_01.018 | ASP --- SAMPLE PROB. PRINTED OUTPUT | 1493 |

CCC0110_01.019 | AIRSCA --- SOURCE PROGRAM (F4,EBCDIC) | 2407 |

CCC0110_01.020 | AIRSCA1 --- DD CARDS | 11 |

CCC0110_01.021 | AIRSCA1 --- SAMPLE PROB. INPUT DATA | 17 |

CCC0110_01.022 | AIRSCA1 --- SAMPLE PROB. PRINTED OUTPUT | 1196 |

CCC0110_01.023 | AIRSCA2 --- DD CARDS | 10 |

CCC0110_01.024 | AIRSCA2 --- SAMPLE PROB. INPUT DATA | 17 |

CCC0110_01.025 | AIRSCA2 --- SAMPLE PROB. PRINTED OUTPUT | 294 |

CCC0110_01.026 | AIRSCA3 --- DD CARDS | 10 |

CCC0110_01.027 | AIRSCA3 --- SAMPLE PROB. INPUT DATA | 17 |

CCC0110_01.028 | AIRSCA3 --- SAMPLE PROB. PRINTED OUTPUT | 291 |

CCC0110_01.029 | ASP --- SOURCE PROGRAM (F4) | 330 |

CCC0110_01.030 | AIRTRANS -- SOURCE PROGRAM (F4) | 4082 |

CCC0110_01.031 | AIR DENSITY TABLE (BCD) | 233 |

Keywords: Monte Carlo method, absorption, collisions, doses, elastic scattering, gamma radiation, inelastic scattering, neutron transport theory, radiation effects, secondary emission, time dependence.