Shielding from solar particle event exposures in deep space John W. Wilson a, *, F.A. Cucinotta a , J.L. Shinn a , L.C. Simonsen a , R.R. Dubey b , W.R. Jordan b , T.D. Jones c , C.K. Chang d , M.Y. Kim e a NASA Langley Research Center, Hampton, VA 23681-0001, USA b Old Dominion University, Norfolk, VA 23508, USA c Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA d Christopher Newport University, Newport News, VA 23601, USA e National Research Council, Washington, DC 20418, USA Received 6 July 1998; received in revised form 4 January 1999 Abstract The physical composition and intensities of solar particle event exposures of sensitive astronaut tissues are examined under conditions approximating an astronaut in deep space. Response functions for conversion of particle ¯uence into dose and dose equivalent averaged over organ tissues are used to establish signi®cant ¯uence levels and the expected dose and dose rates of the most important events from past observations. The BRYNTRN transport code is used to evaluate the local environment experienced by sensitive tissues and used to evaluate bioresponse models developed for use in tactical nuclear warfare. The present results will help to clarify the biophysical aspects of such exposure in the assessment of RBE and dose rate eects and their impact on design of protection systems for the astronauts. The use of polymers as shielding material in place of an equal mass of aluminum would provide a large safety factor without increasing the vehicle mass. This safety factor is sucient to provide adequate protection if a factor of two larger event than has ever been observed in fact occurs during the mission. Published by Elsevier Science Ltd. Keywords: Solar particle events; Shielding; Biological response; Mortality; Tissue environments 1. Introduction Solar cosmic radiation has long been recognized as a serious potential hazard in space operations (Schaefer, 1957). Also it was recognized that the provision of suf- ®cient shielding to keep exposures at low levels increased the complexity of spacecraft with associated increased risks of mechanical failure and tradeo of radiation health risks with the other mission risk became the rule in early space activity. As a result of the national importance of the Apollo mission to land men on the moon, rather high levels of exposure were allowed in the design process as other risks within those missions were also high and a balance of radi- ation risks and the other mission risks were assumed (Billingsham et al., 1965). The exposure limits allowed in the design of the Apollo mission are given in Table 1. With the development of Skylab, Shuttle, and now International Space Station (ISS) the routine nature of space operations has led to a more conservative view of risk acceptability in space exposures (NAS, 1970). Indeed, the NCRP (NCRPM, 1989) has recommended Radiation Measurements 30 (1999) 361±382 1350-4487/99/$ - see front matter Published by Elsevier Science Ltd. PII: S1350-4487(99)00063-3 www.elsevier.com/locate/radmeas * Corresponding author. Tel.: +1-757-864-1414; fax: +1- 757-864-8094. E-mail address: john.w.wilson@larc.nasa.gov (J.W. Wilson)