Copyright 1999 American Society for Microbiology. All rights reserved. X-rays are safe, but these precautions give you some sense of how careful we have to be around even relatively harmless levels of radiation. The problem is that unsafe levels of radiation can mess with the cells and molecules in our body, warping them and even breaking them apart. It does the same thing to microbial cells.
Radiation is measured in units called rads.
A dose of 500 to 1,000 rads is enough to kill a person. The Guinness Book of World Records dubbed it the world's toughest bacterium. Actually no, it's not a spore-former. Anyway, while bacterial spores can endure radiation, none can take nearly as much as D. radiodurans can. Let's first take a quick look at what radiation does to a living thing.