1 Rad is considered dangerous to human life, and 20 Rad/400 Sieverts is considered lethal, when absorbed over the same length of time.
Enjoy!
I met a former NASA employee a few years ago on an airline flight. He was the manager for NASA grant money to various colleges and universities. He was a retired USAF Lt Cl that had served in Vietnam and an alternative Space Shuttle Astronaut.
He was coming back from Dartmouth where he was reviewing the progress on research how zero gravity effects all humans eyeballs that have gone on the international space station.
Every astronaut that went up to the space station becomes near sited. The radiation is also why no human stays there for more than one year.
He stated the biggest problem in sending humans to Mars is the radiation they would absorb and other effects on the human body in the trip getting there. They could build the rocket. Send it to Mars, but the humans might be crippled by the time they got there.

