Re: HAS ANY BODY TRIED THIS?
Isotope Money? If this is what I think it will be, it will not be radioactive. Instead, what they would do is to take some component of the money--the ink, say, or maybe just one small patch of ink--and make the ink from feedstock in which the ratio of the stable isotopes of carbon, C12 and C13, had been deliberately altered from the naturally occuring ratio. This is so difficult to do that counterfeiters would be defeated. However, it would also be so expensive that it would not be worthwhile doing it with ordinary money. They might, however, use it on a controlled delivery of money to criminal gangs. About 20 years ago, when I was on the other side, I suggested this technique for use in controlled deliveries of untaxed diesel to gangs who were removing the chemical markers and selling it for road use. It was rejected, not because they said it would not work, but because they said it would require a change in the law.
One bit of good news though: gold has only one stable isotope.