Companies are loyal to the bottom line, not to you. Don't sacrifice living your life trying to prove yourself trying to be the best employee ever by doing nothing but work. Companies love for you to make extra effort all the time, but if they can make a million dollars by firing you, it doesn't matter how good of an employee you are. Work hard, do your job, but be ready to leave at a moment's notice when something better is around - you REALLY don't owe them anything.
Besides, when he was a little older and more aware of appropriateness, we had a better discussion about which words are appropriate to say in public. It was a much better way to handle it.
NOTE: While it's not VERY radioactive is still IS radioactive. Don't plan a long camping trip there, or decide carry a piece of it around in your pocket. Ummm... I guess unless you like having tumors.