The Radiation Threat to “The Martian” (PDF)

This is something that has been bugging me ever since reading the book:

While Andy Weir does a good job of representing the risks faced by Mark Watney, stranded on Mars and confronting one life-threatening challenge after another, he is silent on the threat of radiation, not just to Mark but particularly to the crew of the Hermes as they contemplate executing a daring rescue mission that more than doubles their time in deep space.

Well, this paper answers all my questions.