The Canadian Nuclear Safety Commission sets upper limits on the amounts of radiation allowable in the workplace. The maximum permissible dose for radiation workers is 5 rem (50 mSv) per year. Cobalt-60 is a radioisotope whose gamma rays are sometimes used in radiation treatment. What is the safe working distance from an unshielded 60Co source that produces 0.800 rad per hour at a distance of 1m? Quote your answer in metres. Assume a 40 hour week, with a three-week holiday period per year. You will need to think about how the intensity falls off with distance; you may assume that the 60Co is a point source, and that the radiation is emitted isotropically. I'm totally stumped with this question. I have no idea how to approach it. I know that I have to get the units to match: 1 rad = 0.01 Gy The equivalent dose of 50mSv per year would be 50mGy per year (assuming that the weight factor equals 1). A friend of mine told me that the intensity is proportional to the 1/ (distance squared)... but how do I get the intensity? Any help would be greatly appreciated!