Radiation Hazard in Space from Solar Particles.

@article{Freier1963RadiationHI,
  title={Radiation Hazard in Space from Solar Particles.},
  author={P Freier and William R. Webber},
  journal={Science},
  year={1963},
  volume={142 3599},
  pages={1587-92}
}
There were about six solar flare events during the last solar cycle which would have exposed a space traveler to serious radiation from solar particles. The radiation from two of these events was intense enough to necessitate extra precautions being taken to protect space travelers.