Realisation and characterisation of Cu-based references for neutron imaging calibration purposes and first results

The long-term purpose of this study is to assess the capabilities of the new Neutron Imaging beamline developed at the LENA facility of Pavia (Italy) for the characterisation of bronze artefacts. In this preliminary work, a set of Cu-based reference alloys has been produced and analysed in order to test and calibrate the facility. The first step involved the production of Cu-based alloys with chemical composition and microstructure similar to ancient artefacts. The chemical composition of the reference alloys was analysed by Optical Emission Spectroscopy. Secondly, some samples were artificially patinated with different chemical treatments obtaining an artificial corrosion products layer comparable to natural corrosion. X-Ray Diffraction, Scanning Electron Microscopy and Raman Spectroscopy have been used to characterise the corrosion patina. The main corrosion products on sulphate-induced patina are cuprite and brochantite, whereas atacamite and clinoatacamite were detected on chloride-induced patinas. Finally, preliminary Neutron Imaging measurements were performed on a first set of coated and uncoated specimens in order to try to correlate the neutrons attenuation coefficients with the chemical compositions with promising results.