X-RAY FLUORESCENCE SPECTROSCOPY FOR DETERMINING COIN COMPOSITION

X-ray fluorescence spectroscopy (XRF) is a well-established analytical technique for the determination of the elemental composition of solid materials in bulk or thin film form. Its speed, reliability and accuracy make it extremely useful for determining the composition of coins from a surface analysis perspective.

In XRF a sample is irradiated by an X-ray beam, which results in ejection of inner shell electrons from the sample atoms. Outer shell electrons take their place and the difference in energy level results in the emission of X-rays (secondary radiation). The wavelength of these X-rays is characteristic for each element present, and the intensity of the emission is related to the concentrations of the elements. The accuracy of metal compositions can be taken down to 0.001%. The penetration of the X-ray into the coin depends on the alloy composition with gold its ~10 micrometers (um) and for copper and silver its higher around 50-100 um.

Currently I have used it in research on the composition of contemporary counterfeit Portrait 8 Reales which is a book currently being written for the American Numismatic Society which is planned for 2013/2014 and William Anton's Anniversary (20th) Forgotten Book. The study of Canadian Blacksmith Tokens and Kleeberg Contemporary Counterfeit 2 Reales, World Contemporary Counterfeits, Off-Metal Errors and other series have been currently looked at to help explain questions on compositions and possible origins of these issues.

I am offering a service for people doing research on coins and my fees are minimal as the important thing is to get good data out to projects currently in progress to better help and understand some of the questions we have studying coins of questionable origins and/or production methods.

Any person undertaking a research project can contact me at johnmenc@optonline.net with the details of their project and coins. People are welcome to see a current project recently done for Mike Diamond in Coin World in the October 15 issue of Collectors Clearinghouse on the 1941 brassy cent in which its mystery has been now unraveled with the help of XRF analysis.

Wayne Homren, Editor

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