Determination of stable isotope ratios using nuclear reaction analysis coupled with a particle–gamma coincidence method

Abstract

A non-destructive standard-free analytical method of obtaining stable isotope ratios in materials using nuclear reactions excited by an 11.75 MeV proton beam is demonstrated for a special ⁶³Cu/⁶⁵Cu target characterized traceably by Rutherford backscattering spectrometry (using 2.2 MeV protons). The method is general and is capable of being a useful alternative to standard ICP-MS methods. Relatively high energy proton beams are required to excite multiple isotopes of most elements of interest, and the many resulting nuclear reaction products are filtered by coincidence methods to characterize the desired isotope ratios. Specifically: the use of particle–gamma coincidences permits identification of specific channels populated in the nuclear reaction and avoids or minimizes typical drawbacks of this method including high backgrounds and interfering reactions. The test Cu target was a sandwich of a natural Cu and an enriched ⁶⁵Cu foil, and particle–gamma coincidences were measured for the reactions ⁶³Cu(p,πγ){⁶³Cu,⁶⁰Ni} and the corresponding reactions for ⁶⁵Cu (where “π” represents the energetic charged particle reaction product: proton or alpha). Limitations of the method, and applications in cultural heritage and other fields are discussed.