Sometime after World War II, extremely sensitive radiation detection equipment became available. A tiny, even microscopic, amount of material could be placed in one of these devices and a complete qualitative and quantitative record of every single radio-isotope present in the sample would be assayed.

The only problem with this was the material used to construct these devices was itself contaminated by fallout from the nuclear weapons tests of the postwar era. You simply could not find metal ores that were not already saturated with fission products from nuclear testing. The radiation emitted by this residual fallout would overwhelm the radiation from the test samples and it was impossible to get a good reading. In other words, an additional level of "background" radiation was superimposed on the radiation from natural sources and it often totally obscured the radiation from the sample being tested.

The problem was solved by building the sample chambers for this equipment out of steel recovered from the thick armor plating of pre-1945 mothballed battleships. The armor plating was removed, the outer layers were milled off, and the resulting uncontaminated steel was not only free from weapons test debris, it also provided shielding from any other radiation present in the environment. Any radioactivity present in this metal was strictly from natural sources, it had always been there, and could be subtracted as "background".