This is one of those things where what you don't know will harm you. Knowledge on the subject of a nuclear or dirty bomb terrorist attack can save your life. Ignorance will kill you.
First I have to tell you that you need to be worried enough, to do what you need to do to stay alive, through a dirty bomb or nuke attack. Do not be discouraged, keep reading to the part where it tells you what to do about it.
Graham Allison, director of the Belfer Center for Science and International Affairs at Harvard University and former Assistant Secretary of Defense under President Clinton, said that he is surprised that we have not already been hit with a dirty bomb by terrorists. He said it is even more surprising that Israel has not experienced one. He went on to express the opinion that this sort of attack pales into insignificance compared to the prospect of a terrorist attack using a nuclear weapon.
Allison said that the equivalent of a 15 kiloton nuclear bomb would fit inside the van that Timothy McVeigh used in Oklahoma City. He said that a nuke instead of planes in the World Trade Center would have taken out the whole Southern tip of Manhattan.
Okay. I hate all this myself, but as awful as this all sounds, Allison still thinks we need to know how to prepare for nuclear terrorist attacks because there are effective things we can do about it.
Homeland Security has a succinct 10 page guide on what to do if a nuclear disaster is imminent. They say in the guide that they expect most people to begin reading at the last minute. I certainly hope that my readers are not going to do this. You should know a lot more than the 10 page guide in order to survive and stay healthy, but it is better than nothing. It does give you a better chance.
Here is a link to the PDF of it, I hope you print it out immediately and even read it and get the supplies ready that are suggested. I am posting this stuff every day because I do not want people, including, you, dear reader, to die when you don't need to. Read it. Act on it. Stay alive and healthy.