Answer to Question #3210 Submitted to "Ask the Experts"

To my knowledge, the only World's Fair at which dimes were irradiated with neutrons was the 1964 World's Fair in New York. Nevertheless, the irradiation of dimes (over one million were done) was a common practice at the American Museum of Atomic Energy in Oak Ridge,Tennessee, during the 1950s and 1960s. Dimes were also irradiated at Oak Ridge National Laboratory, but I am unsure of when this was done, but it was probably in the late 1940s and/or the early 1950s.

Today, any induced activity in the dimes has decayed to the point that it cannot be detected without a great deal of effort. This is because the key radionuclide produced in the dimes, ¹¹⁰Ag (silver-110), has a half-life of 25 seconds. A little ¹⁰⁸Ag was produced, but it also has a very short half-life: 2.39 minutes. In other words, the coins are not "hot."

It is impossible to say exactly what the activities would have been at the time that the dimes were irradiated since I have not seen the results of any analyses that were done then. But it is possible to hazard a guess, and I did some back-of-the-envelope type calculations. While the results suggest that the maximum induced activity would have been on the order of 20 microcuries (and this would decay away quickly), it is probable that the actual activities were quite a bit lower. Keep in mind that I had to make wild guesses as to what the irradiation times and the neutron fluence rates were.

For what it is worth, the dimes that were irradiated at Oak Ridge National Laboratory and the American Museum of Atomic Energy were sealed inside a plastic and metal case as a keepsake. The dimes irradiated at the New York World's Fair were put in blue plastic holders with the Atomic Energy Commission logo on the back. Some additional information and photographs can be seen at a Web site that I manage.

Paul Frame, CHP, PhD