How many inches of lead would it take to stop the gamma rays equal to 8 inches of concrete ? 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. 
 A: 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.

A: Radiation shielding
1 inch lead same as:

*

*1.5 inch Stainless steel

*1.7 inch cast iron

*4.7 inch concrete

The lead cost for surface cover is
30% cheaper than concrete.
Cast iron 4 times cheaper than lead.
Cast iron 5 times cheaper than concrete.
For equal shielding \$ per ft$^2$

*

*Cast iron \$ 7.65

*Lead   \$ 31

*Concrete \$ 39.95

*Stainless steel \$
90

1 inch of gold same as
1.7 inches of lead
cost ? About 4 million dollars per ft$^2$ coverage
The shielding would be equivalent to 8 inch of concrete cover.
