They pop a few coins in a nuke reactor... (neutrons get added in proportion to each element's propensity to absorb neutrons) ... in a "safe" place... and then take 'em out... and they can determine % element composition of each coin by the amount of neutrons emitted over a period of time ...emitted by each element's propensity to "let go" of an absorbed neutron. https://www3.nd.edu/~nsl/Lectures/phys178/pdf/chap2_6.pdf
Oak Ridge National Laboratory made 'em. American Museum of Atomic Energy made 'em. and "Mid-south Fair's Atomic Energy Exhibit Neutron Irradiated" This site (third article down) has mucho info. (par example: UCNC Union Carbide Nuclear Corporation) http://www.chicagocoinclub.org/chatter/2012/Apr/ www.cointalk.com/threads/irradiated-mercury-dime.36411/
"The H Denarius" by Richard Witschonke in Numismatic Chronicle 2008 actually mentions a coin being tested by neutron activation analysis. The denarius in question was in the BNF in Paris and with a weight of 3.17g was far below the theoretical weight of an official coin of circa 4.2g. Crawford in Roman Republican Coinage had rejected this example, apparently assuming it to be an ancient plated forgery, and with it this denarius variety altogether but neutron activation analysis revealed a purity of approximately 97% silver, proving once and for all that it wasn't plated. Additionally, a specific gravity test showed that another example from the same dies was almost certainly solid silver.
