COMPOSITE SHIELDS FOR SPACE POWER SYSTEMS-

RECENTLY CONCEIVED RADIATION TRANSPORT ANALYSIS TECHNIQUES WILL BE STUDIED TO ASSESS THEIR USE IN SPACE NUCLEAR POWER SHIELD DESIGN OPTIMIZATION. THE ULTIMATE AIM IS TO DETERMINE OPTIMAL COMPOSITIONS AND CONFIGURATIONS OF SHIELD COMPONENTS FOR THE PRO- TECTION OF SPACE SYSTEMS AGAINST MIXED RADIATION FIELDS FROM INTERNAL AND EXTERNAL SOURCES. PARTICULAR ATTENTION WILL BE PAID TO USING COMPOSITE AND LAYERED SHIELD ELEMENTS AND TO INCORPORATING STREAMING PATHS IN THE SHIELD TO DIVERT RADIATION AWAY FROM CRITICAL AREAS SUCH AS MICROELECTRONIC COMPONENTS. SIGNIFICANT POTENTIAL SAVINGS (REDUCED MASS FOR A SPECIFIED TARGET DOSE) ARE POSSIBLE. THE TECHNIQUES TO BE STUDIED ARE THE INVERSE MONTE CARLO METHOD AND THE BACK-PROJECTION ANGULAR FLUX ESTIMATOR. THESE ARE POWERFUL METHODS THAT HAVE BEEN RECENTLY DEVELOPED AND APPLIED TO SIMPLE PRO- BLEMS IN OTHER FIELDS. INVERSE MONTE CARLO IS A NON- ITERATIVE METHOD FOR SOLVING INVERSE AND OPTIMIZA- TION PROBLEMS, AND THE BACK-PROJECTION ESTIMATOR IS A DIRECT WAY TO OBTAIN ANGULAR FLUX IN A UNIQUE DIREC- TION AT A POINT, WITHOUT THE USE OF FINITE SPATIAL AND ANGULAR INTERVALS. THE INTENT OF THIS PROJECT IS TO DE- TERMINE IF THE METHODS ARE CAPABLE OF BEING USED TO FIND OPTIMUM COMPOSITION AND PLACEMENT OF SHIELD ELEMENTS FOR MIXED-FIELD SHIELDING IN COMPLEX GEOM- ETRIES. THE MAIN ADVANTAGES OF THE METHODS ARE EFFI- CIENCY AND ABILITY TO HANDLE COMPLEX PROCESSES AND THREE-DIMENSIONAL GEOMETRIES. IF PHASE I IS SUC- CESSFUL, THE TECHNIQUES WILL BE APPLIED IN PHASE II TO THE DESIGN OPTIMIZATION OF SHIELDS FOR SPACE NUCLEAR POWER SYSTEMS. IN PARTICULAR, OPTIMUM MATERIAL COMPOSITIONS TO SHIELD AGAINST MIXED RADIATION FIELDS, INCLUDING THE COMPLICATING EFFECTS OF SECONDARY (N,Y)RADIATION, AND OPTIMUM "GOOD-GEOMETRY" CON- CEPTS WILL BE IDENTIFIED.