So my question is, how long can you be exposed to a gamma radiation for? Specifically, I've been working with a sealed cobalt-60 source for a final presentation. Now my professor noted to me that these sources we're using aren't radioactive enough to cause us any harm. However, I've been working with this source for approximately 3-4 hours at a time for approximately 4 different days now. Its a cobalt-60 source labelled at 0.1microcuries. Can someone provide inside into what the difference between all the units of radiation are including rad,rem,curie,roentgen, becquerel, etc. I've found so many units its hard to differentiate and make sense of them all. I also want to make sure I'm not overstepping my bounds when it comes to the amount of time I'm being exposed to this source for. Also whether or not the headaches i get aren't just a placebo effect and worrying too much about it. Thanks!