A RADIATION SHIELDING CODE FOR SPACECRAFT AND ITS VALIDATION zyxw J. L Shinn', F. A. Cucinotta2, R. C. Singleterry', J. W. Wilson', F. F. Badavi3, G. D. Badhwa?, J. Miller4,C. Zeitlin4,and zyxwvu L. Heilbronn4,R. K. Tri~athi'.~, M. S. Clowdsley6, and J. H. Heinbocke16 'NASA Langley Research Center, Hampton, VA 2NASAJohnson Space Center, Houston, TX 3ChristopherNewport University, Newport News, VA 4LawrenceBerkeley National Laboratory, Berkeley, CA 5NationalResearch Council, Washington, DC 601d Dominion University, Norfolk, VA ABSTRACT KEY WORDS: Spacecraft Design; Space Radiation; Radiation Shielding The HZETRN code, which uses a deterministic approach pioneered at NASA Langley Research Center, has been developed over the past decade to evaluate the local radiation fields within sensitive materials (electronic devices and human tissue) on spacecraft in the space environment. The code describes the interactions of shield materials with the incident galactic cosmic rays, trapped protons, or energetic protons from solar particle events in free space and low Earth orbit. The content of incident radiations is modified by atomic and nuclear reactions with the spacecraft and radiation shield materials. High-energy heavy ions are fragmented into less massive reaction products, and reaction products zyxwvu are produced by direct knockout of shield constituents or from de-excitation products. An overview of the computational procedures and database which describe these interactions is given. Validation of the code with recent Monte Carlo benchmarks, and laboratory and flight measurement is also included. 1. INTRODUCTION There are three sources of naturally occurring ionizing radiations which concern spacecraft designers. They are galactic cosmic rays (GCR) composed of mainly protons with ten percent