I have searched high and mighty on google and it is hard to find a comparison chart of different materials and their effectiveness to stop radiation from fallout. I am assuming the fallout source is of a standard thermonuclear weapon of 2 megatons at a distance of 10 miles.
So let us say I would like to compare lead to 8 inches of concrete or 3 feet of earth how much thickness of lead would it take to stop the same amount of gamma rays emanating from the fallout particles suspended in the air at their maximum emission time.
A trained physicist may have come across this question.
Best Answer
Lead and concrete affect radiation in different ways: There's not a simple ratio between their effectiveness. For example, I've attached below a table of thicknesses for gamma ray "half value layers": the amount of material needed to reduce gamma's from a particular source by 50%. Note that lead is from 4 to 10 times better (thinner) than concrete. (The table is from a nice presentation of how to do basic shielding calculations)
But generally, about a factor of 5-6 over concrete would be about right. So your 8 inches of concrete would be the equivalent of about 1.5 or 2 inches of lead.