NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROBLEM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, UNUSUAL FEATURES OF THE PROGRAM, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES

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Program name | Package id | Status | Status date |
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SPARES | CCC-0148/01 | Tested | 01-OCT-1977 |

Machines used:

Package ID | Orig. computer | Test computer |
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CCC-0148/01 | IBM 370 series | IBM 370 series |

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3. DESCRIPTION OF PROBLEM OR FUNCTION

(A). The ELMC Code calculates the electron number, energy, and angular fluence resulting from the penetration of a specified initial spectrum on a multilayered one-dimensional shield.

(B). Data from the ELMC Electron Monte Carlo Code have been used in EPEN to formulate analytic expressions to describe electron number penetration and the penetrating energy spectrum. Dose and spectral data are obtained for a set of initial energies, and the results are then weighted by the incident spectra of interest and summed for the final solution.

(C). The bremsstrahlung dose resulting from electrons incident on a shield is calculated. Either one-dimensional, multilayer slab geometrie or three-dimensional geometries can be treated.

(D). HEVPART calculates the penetrating energy spectrum, LET spectrum, and absorbed dose in multilayered slabs resulting from a fluence of protons, He, or heavy ions. Results for three-dimensional geometries can also be obtained to describe space vehicle structures.

(E). The penetrating proton energy spectrum and the resulting secondary protons, neutrons, and gamma rays are calculated in SECPRO for multilayered shields. Dose and LET spectral data are also given. The recoiling nuclei dose resulting from the penetrating proton and neutron spectra are also given.

(F). TANDE was designed to calculate the Van Allen belt electron and proton fluxes and fluences, encountered in or near earth trajectories.

(A). The ELMC Code calculates the electron number, energy, and angular fluence resulting from the penetration of a specified initial spectrum on a multilayered one-dimensional shield.

(B). Data from the ELMC Electron Monte Carlo Code have been used in EPEN to formulate analytic expressions to describe electron number penetration and the penetrating energy spectrum. Dose and spectral data are obtained for a set of initial energies, and the results are then weighted by the incident spectra of interest and summed for the final solution.

(C). The bremsstrahlung dose resulting from electrons incident on a shield is calculated. Either one-dimensional, multilayer slab geometrie or three-dimensional geometries can be treated.

(D). HEVPART calculates the penetrating energy spectrum, LET spectrum, and absorbed dose in multilayered slabs resulting from a fluence of protons, He, or heavy ions. Results for three-dimensional geometries can also be obtained to describe space vehicle structures.

(E). The penetrating proton energy spectrum and the resulting secondary protons, neutrons, and gamma rays are calculated in SECPRO for multilayered shields. Dose and LET spectral data are also given. The recoiling nuclei dose resulting from the penetrating proton and neutron spectra are also given.

(F). TANDE was designed to calculate the Van Allen belt electron and proton fluxes and fluences, encountered in or near earth trajectories.

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4. METHOD OF SOLUTION

(A). ELMC employs the Monte Carlo method with angular scattering treated by the method of Leiss, Penner, and Robinson. Energy loss is treated by the continuous slowing down approximation, and energy straggling is not treated. The energy dose and angular deflections are calculated in path length segments of delta x, where delta x can be adjusted by input data and made proportional to particle energy if desired.

(B). The EPEN code calculates the absorbed dose at a point of interest caused by electrons penetrating a shielding system. The penetrating electron energy spectrum is also calculated. Multilayer shields can be treated.

(C). The bremsstrahlung differential energy spectrum produced in a material is estimated by an expression given by Wyard.

The photon energy spectrum is then transported through the remaining shielding material by the use of ray theory plus buildup factors.

Two basic calculational modes are available. In the surface production option, the bremsstrahlung is all produced at the surface of the shield. In the volume production option, the attenuation of the electron spectrum is considered, and the bremsstrahlung source is volume distributed. (BREMS).

(D). The straight ahead approximation is used in HEVPART and nuclear interactions are neglected to provide a rapid solution of the heavy ion transport problem. The range-energy and stopping power tables of Barkas and Berger are used. Low energy correction factors are employed to describe the changes in stopping power resulting from electron capture.

(E). The first collision approximation and the straight ahead approximation are employed in SECPRO to simplify the cascade transport problem. Neutron induced protons are also calculated to refine the neutron dose estimate. The code employs the tabulated Barkas and Berger range energy data and the secondary particle production data of Bertini for numerical integration of the primary and secondary particle fluxes.

(F). The user supplies to TANDE description of a vehicle trajectory and radiation-environment data. The program calculates electron or proton flux rate and time-integrated flux along the trajectory.

The general then compute radiation flux at these points.

Given a description of the orbit and the point of injection, subject trajectory points are calculated as a function of time, using orbital flight equations. The trajectory points are converted to McIlwain's geomagnetic coordinates (B,L, and R, lamda).

Proton or electron flux at each point is determined by a table lookup and interpolation. Numerical integration (in conjunction with an interpolation scheme on B and L) gives a time-integrated flux for each point. A table lookup and interpolation on an array of spectral coefficients determines the spectral coefficients for the point. The flux at the point, dose-conversion factors, and the spectral coefficients are then used to determine dose rate and total dose at the point.

Angular distribution is determined for each trajectory point by solution of a pitch angle distribution function.

The code is designed so that new experimental data on the radiation environment and on the interaction of radiation with matter can be accepted.

The following general methods are followed:

1. calculation of the spacecraft trajectory in B, L, and t coordinates,

2. devising a mathematical representation of the space-radiation environment, including geomagnetically trapped radiation (Van Allen belts), solar particle event radiation, and galactic cosmic radiation;

3. determination of the radiation flux and energy spectra encountered in a given space mission.

(A). ELMC employs the Monte Carlo method with angular scattering treated by the method of Leiss, Penner, and Robinson. Energy loss is treated by the continuous slowing down approximation, and energy straggling is not treated. The energy dose and angular deflections are calculated in path length segments of delta x, where delta x can be adjusted by input data and made proportional to particle energy if desired.

(B). The EPEN code calculates the absorbed dose at a point of interest caused by electrons penetrating a shielding system. The penetrating electron energy spectrum is also calculated. Multilayer shields can be treated.

(C). The bremsstrahlung differential energy spectrum produced in a material is estimated by an expression given by Wyard.

The photon energy spectrum is then transported through the remaining shielding material by the use of ray theory plus buildup factors.

Two basic calculational modes are available. In the surface production option, the bremsstrahlung is all produced at the surface of the shield. In the volume production option, the attenuation of the electron spectrum is considered, and the bremsstrahlung source is volume distributed. (BREMS).

(D). The straight ahead approximation is used in HEVPART and nuclear interactions are neglected to provide a rapid solution of the heavy ion transport problem. The range-energy and stopping power tables of Barkas and Berger are used. Low energy correction factors are employed to describe the changes in stopping power resulting from electron capture.

(E). The first collision approximation and the straight ahead approximation are employed in SECPRO to simplify the cascade transport problem. Neutron induced protons are also calculated to refine the neutron dose estimate. The code employs the tabulated Barkas and Berger range energy data and the secondary particle production data of Bertini for numerical integration of the primary and secondary particle fluxes.

(F). The user supplies to TANDE description of a vehicle trajectory and radiation-environment data. The program calculates electron or proton flux rate and time-integrated flux along the trajectory.

The general then compute radiation flux at these points.

Given a description of the orbit and the point of injection, subject trajectory points are calculated as a function of time, using orbital flight equations. The trajectory points are converted to McIlwain's geomagnetic coordinates (B,L, and R, lamda).

Proton or electron flux at each point is determined by a table lookup and interpolation. Numerical integration (in conjunction with an interpolation scheme on B and L) gives a time-integrated flux for each point. A table lookup and interpolation on an array of spectral coefficients determines the spectral coefficients for the point. The flux at the point, dose-conversion factors, and the spectral coefficients are then used to determine dose rate and total dose at the point.

Angular distribution is determined for each trajectory point by solution of a pitch angle distribution function.

The code is designed so that new experimental data on the radiation environment and on the interaction of radiation with matter can be accepted.

The following general methods are followed:

1. calculation of the spacecraft trajectory in B, L, and t coordinates,

2. devising a mathematical representation of the space-radiation environment, including geomagnetically trapped radiation (Van Allen belts), solar particle event radiation, and galactic cosmic radiation;

3. determination of the radiation flux and energy spectra encountered in a given space mission.

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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

(A). Validity of results in ELMC is dependent on the choice of delta x, and the number of histories.

(B). The basic accuracy of EPEN is determined by the Monte Carlo data. In addition, the analytic fits developed have ranges of validity.

(C). The volume source options in BREMS must be carefully chosen to match the electron energy and shield configuration.

(D). As secondary interactions are neglected in HEVPART, the shield should then be compared to the mean free path of the ion.

(E). In SECPRO secondary data is provided only for aluminum and H2O. The shield thickness must be smaller than a proton mean free path to remain within the valid range of the first collision appro- ximation.

(F). The principle restriction in the use of TANDE is that the trajectories selected for analysis can only be evaluated at B,L points described by the flux maps.

(A). Validity of results in ELMC is dependent on the choice of delta x, and the number of histories.

(B). The basic accuracy of EPEN is determined by the Monte Carlo data. In addition, the analytic fits developed have ranges of validity.

(C). The volume source options in BREMS must be carefully chosen to match the electron energy and shield configuration.

(D). As secondary interactions are neglected in HEVPART, the shield should then be compared to the mean free path of the ion.

(E). In SECPRO secondary data is provided only for aluminum and H2O. The shield thickness must be smaller than a proton mean free path to remain within the valid range of the first collision appro- ximation.

(F). The principle restriction in the use of TANDE is that the trajectories selected for analysis can only be evaluated at B,L points described by the flux maps.

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6. TYPICAL RUNNING TIME

No statistics are available to determine typical running time. Estimated running time for the sample problems are tabulated below.

CODE CORE SIZE(GO STEP) RUNNING TIME(Sec)

IBM 360/91

----------------------------------------------

(A). ELMC 246K 49.54

(B). EPEN 162K 0.96

(C). BREMS 184K 0.72

(D). HEVPART 186K 0.82

(E). SECPRO 296K 3.11

(F). TANDE 314K 5.09

No statistics are available to determine typical running time. Estimated running time for the sample problems are tabulated below.

CODE CORE SIZE(GO STEP) RUNNING TIME(Sec)

IBM 360/91

----------------------------------------------

(A). ELMC 246K 49.54

(B). EPEN 162K 0.96

(C). BREMS 184K 0.72

(D). HEVPART 186K 0.82

(E). SECPRO 296K 3.11

(F). TANDE 314K 5.09

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10. REFERENCES

- John A. Barton, B.W. Mar, G.L. Keister, W.R. Doherty, J.R.

Benbrook, W.R. Sheldon, J.R. Thomas, K. Moriyasu, and M.C.

Wilkinson:

"Computer Code for Space Radiation Environment and Shielding"

Volume I and II (August 1964).

- John A. Barton, B.W. Mar, G.L. Keister, W.R. Doherty, J.R.

Benbrook, W.R. Sheldon, J.R. Thomas, K. Moriyasu, and M.C.

Wilkinson:

"Computer Code for Space Radiation Environment and Shielding"

Volume I and II (August 1964).

CCC-0148/01, included references:

- Paul G. Hahn:"Space Radiation Environment and Shielding System"

AS 2807 (1969).

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CCC-0148/01

File name | File description | Records |
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CCC0148_01.002 | ELMC SOURCE - F4 EBCDIC | 1491 |

CCC0148_01.003 | RANDM SUBROUTINE - F4 EBCDIC | 39 |

CCC0148_01.004 | ELMC JOB CONTROL | 2 |

CCC0148_01.005 | ELMC SAMPLE PROBLEM INPUT | 195 |

CCC0148_01.006 | ELMC SAMPLE PROBLEM OUTPUT | 1462 |

CCC0148_01.007 | EPEN SOURCE - F4 EBCDIC | 1313 |

CCC0148_01.008 | EPEN JOB CONTROL | 4 |

CCC0148_01.009 | EPEN SAMPLE PROBLEM INPUT | 99 |

CCC0148_01.010 | EPEN SAMPLE PROBLEM OUTPUT | 140 |

CCC0148_01.011 | BREMS SOURCE - F4 EBCDIC | 1563 |

CCC0148_01.012 | BREMS JOB CONTROL | 4 |

CCC0148_01.013 | BREMS SAMPLE PROBLEM INPUT | 64 |

CCC0148_01.014 | BREMS SAMPLE PROBLEM OUTPUT | 83 |

CCC0148_01.015 | HEVPART SOURCE - F4 EBCDIC | 1375 |

CCC0148_01.016 | HEVPART JOB CONTROL | 4 |

CCC0148_01.017 | HEVPART SAMPLE PROBLEM INPUT | 80 |

CCC0148_01.018 | HEVPART SAMPLE PROBLEM OUTPUT | 178 |

CCC0148_01.019 | SECPRO SOURCE - F4 EBCDIC | 2005 |

CCC0148_01.020 | SECPRO JOB CONTROL | 4 |

CCC0148_01.021 | SECPRO SAMPLE PROBLEM INPUT | 353 |

CCC0148_01.022 | SECPRO SAMPLE PROBLEM OUTPUT | 762 |

CCC0148_01.023 | TANDE SOURCE - F4 EBCDIC | 3503 |

CCC0148_01.024 | TANDE JOB CONTROL | 5 |

CCC0148_01.025 | TANDE SAMPLE PROBLEM INPUT | 491 |

CCC0148_01.026 | TANDE SAMPLE PROBLEM OUTPUT | 407 |

Keywords: Monte Carlo method, electron spectra, electrons, shields.