Originally posted by Raskolnikov
Simple slabs of lead can sheild radiation quite effectively and make such measures meaningless.

Measures are never going to be meaningless , no matter how much lead you use for shielding there will always be a significant reading difference in the measurements.

And for the Mahatten project , that was more than half a century ago beside it was the first nuke in history ... No one could have guessed what it was.
But now , you can easily measure any site's radiation for nuclear activity confirmation.