**1. NAME AND TITLE**

SPARES: Space Radiation Environment and Shielding Code System.

**AUXILIARY ROUTINES**

(A) ELMC: Electron Monte Carlo Code.

(B) EPEN: Electron Penetration Code.

(C) BREMS: Bremsstrahlung Code.

(D) HEVPART: Heavy Particle Penetration Code.

(E) SECPRO: Secondary Proton Penetration Code.

(F) TANDE: Trajectory and Environment Code.

**2. CONTRIBUTOR**

Aerospace Group, The Boeing Company, Seattle, Washington.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/75/91.

Random Number Generator in ELMC is in Assembly Language.

**4. NATURE OF PROBLEM SOLVED**

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

(B) Data from ELMC is 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 in BREMS. Either one-dimensional, multilayer slab geometries 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.

**5. 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 x, where x can be adjusted by input data and made proportional to particle energy if desired.

(B) EPEN 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 in BREMS. 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.

(D) 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 a description of a vehicle trajectory and radiation-environment data. TANDE calculates electron or proton flux rate and time-integrated flux along the trajectory. The general procedure is to give as input or calculate trajectory points and 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,lambda).

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.

TANDE 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:
calculation of the spacecraft trajectory in B, L, and t coordinates; devising a mathematical
representation of the space-radiation environment, including geomagnetically trapped radiation
(Van Allen belts), solar particle event radiation, and galactic cosmic radiation; and determination of
the radiation flux and energy spectra encountered in a given space mission.

**6. RESTRICTIONS OR LIMITATIONS**

(A) Validity of the results in ELMC is dependent on the choice of 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 approximation.

(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.

**7. TYPICAL RUNNING TIME**

No statistics are available to determine typical running time. Estimated running time in seconds
for the sample problems and core size for each calculation is: ELMC, (246 K) 49.54 sec.; EPEN,
(162 K) 0.96 sec.; BREMS, (184 K) 0.72 sec.; HEVPART, (186 K) 0.82 sec.; SECPRO, (296 K)
3.11 sec.; and TANDE, (314 K) 5.09 sec.

**8. COMPUTER HARDWARE REQUIREMENTS**

The SPARES codes were designed to run on the IBM 360 with standard I-O and a maximum of
3 tape units or direct access devices.

**9. COMPUTER SOFTWARE REQUIREMENTS**

SPARES is operable on the IBM 360/75/91 Operating System using OS-360 FORTRAN H compiler.

The random number generator required in ELMC is included on the master tape.

**10. REFERENCES**

a. Included in package:

P. G. Hahn, "Space Radiation Environment System," AS 2807 (1969).

b. Background information:

J. 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 Codes for Space Radiation Environment and Shielding," Volume I and II (August 1964).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document (10.a) and one (1.2MB) DOS diskette which contains the
source codes and sample problem input and output.

**12. DATE OF ABSTRACT**

February 1972; revised December 1984.

**KEYWORDS:** SPACE RADIATION; ELECTRON; BREMSSTRAHLUNG; PROTON; TRAJECTORY