Source: Wikipedia
Y-12 National Security Complex was built as part of the Manhattan Project for the purpose of enriching uranium for the first atomic bombs.
The Chief Engineer of the Manhattan District, Colonel James C. Marshall, and his deputy, Lieutenant Colonel Kenneth D. Nichols, discovered that the electromagnetic isotope separation process would require 5,000 short tons (4,500 tonnes) of copper, which was in desperately short supply. However, they realized that silver could be substituted, in an 11:10 ratio.
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