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Space Radiation Health Research: Narrowing the Uncertainties in Exploration Risk.  Paul Todd, Techshot, Inc., Greenville, IN 47124. 

   For fifty years we have known three broad categories of ionizing radiations in space. Galactic cosmic radiation (GCR) consists of nuclei of atoms of all species traveling at high energy and having similar elemental distribution to that of the universe and includes biologically damaging iron nuclei at a significant fraction of the dose.  Solar protons and electrons constantly diffuse away from the sun forming the solar wind and radiation belts; these radiations are similar to x rays in their biological effect.  Solar proton events (SPE’s) episodically release protons of high energy (10-300 MeV) and intensity into the solar system in directions and at times that are difficult to predict.  Dose rates and physical spectra of these three radiations have been extensively characterized, but their risks to space travelers are only understood with great uncertainties. For more than three decades scientists have pointed out that one great unknown risk is the combination of space flight factors and radiation exposure.  Flight crews are known to exhibit such symptoms as anemia, immunodeficiency, bone and muscle loss and intellectual impairment.   The three broad radiation effects under study in U. S. ground-based research are: risk of cancer due to GCR, risk of neurological and behavioral decrements due to continuous GCR exposure, and risk of acute whole-body effects due to SPE’s.  Each speaker in this session will present research concerning each of these risks.   Research in the U. S. is being performed on the biological effects of GCR by more than 100 investigators in groups that utilize the radiations produced at the NASA Space Radiation Laboratory (NSRL), a sophisticated facility installed at Brookhaven National Laboratory.  Protons and heavy ions found in the GCR (C, Ne, Si, Ti, Fe) are accelerated to energies of several GeV, spread into wide (20 cm) beams and used to expose cells, molecules and organisms to simulated GCR particles.  Research on the biological effects of SPE’s is performed at medical proton accelerators, such as those at Loma Linda University and Indiana University, which provide medical dosimetry systems.  Speakers in this session will describe results of research performed at these facilities. Support: NASA Contracts NNJ07JA10C and NNJ06HE95A.