Transmission of X and γ-rays to differentiate tumbaga from gold and gilded copper

•Attenuation measurements of monoenergetic X and γ-rays, in addition to energy-dispersive X-ray fluorescence analysis, can help to differentiate a gold-alloy from gilded copper or tumbaga created by the Moche, a population from the North of Peru (1st to 6th century C.E.). Tumbaga indicates a poor gold alloy subject to surface depletion gilding. Monoenergetic X-rays of 25 keV were produced by irradiating a Sn-secondary target, while γ-rays of 60 keV were generated by an Am-241 radioactive source. In many cases, the differentiation between an artefact on gold alloy, or on tumbaga (the last being a poor gold alloy subject to depletion gilding), and, sometimes, on gilded copper, is not easy. Their aspect is often similar, and energy-dispersive X-ray fluorescence analysis, which is one of the few non-destructive and non-invasive technique suited to analyze gold sheets, is sometimes not able to solve the question on the basis of altered Au-L, Cu-K, Cu-K/Au-L- ratios, as in other similar cases. For that reason, X-rays from a Sn secondary target, and 26.4 and 59.6 keV γ-rays emitted by an Am-241 radioactive source were employed in transmission mode as an additional differentiation method.