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RSIC CODE PACKAGE CCC-093

1. NAME AND TITLE

MCFLARE: Monte Carlo Code to Simulate Solar Flare Events and Estimate Probable Doses Encountered on Interplanetary Missions.

This code package is retained by RSIC to preserve space technology developed in the 1960s.

2. CONTRIBUTOR

NASA Lewis Research Center, Shielding Analysis Section, Nuclear Systems Division, Cleveland Ohio.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 7090 and 7094.

4. NATURE OF PROBLEM SOLVED

The program estimates probability of exceeding dose from solar flares encountered on an interplanetary mission for various (input) shields.

5. METHOD OF SOLUTION

MCFLARE uses Monte Carlo methods to simulate solar flare occurrences during an interplanetary space voyage. The total biological dose inside a shielded crew compartment due to the flares encountered is determined. MCFLARE evaluates the doses obtained on a large number of trips having identical trajectories. From these results, a dose DP having a probability p of not being exceeded during the voyage can be determined as a function of p for any shield configuration.

The user of the code selects any number of solar flares considered to be representative of the ones that will occur during future solar active periods. The flares are assumed to occur randomly during these periods. The dose at a distance of l AU (astronomical unit = 1.496 x 108 km.) from the sun from each of these flares behind any shield configuration investigated is input to MCFLARE. MCFLARE accounts for the dependence of the dose received from a flare on the distance from the sun according to a (1/r) variation, where r is the distance from the sun and the exponent alpha is assigned any integral value including zero. From trajectory parameters, which are also input to the computer program, the distance from the sun as a function of time during the trip is calculated.

6. RESTRICTIONS OR LIMITATIONS

Limitations on number of bins used for scoring are:

Number of different flare events considered < 25

Number of different shields considered < 7

Number of dose bins of unit width to be used < 900

7. TYPICAL RUNNING TIME

Sample problem described in reference took 2 minutes for 13 flare events, 40000 trips. Estimated running time of packaged sample problem: 0.11 hours.

8. COMPUTER HARDWARE REQUIREMENTS

The code was designed for a 32 K IBM 7094-II using standard I-O.

9. COMPUTER SOFTWARE REQUIREMENTS

The code is operable on the IBM 7090/7094 IBSYS Operating System using IBJOB Processor. A random number generator is included in this package.

10. REFERENCE

G. P. Lahti, I. M. Karp, and B. M. Rosenbaum, "MCFLARE, A Monte Carlo Code to Simulate Solar Flare Events and Estimate Probable Doses Encountered on Interplanetary Missions," NASA TN D-4311 (February 1968).

11. CONTENTS OF CODE PACKAGE

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

12. DATE OF ABSTRACT

May 1969; updated July 1981, February 1985.

KEYWORDS: SPACE RADIATION; ENVIRONMENTAL DOSE; MONTE CARLO