On the use of neutron tomography for morphological analysis of highly corroded Kofun-period iron weapon fragments supported by quantitative neutron diffraction analysis and X-ray-based techniques

During the Kofun period (mid-3rd through early 7th century AD) of Japan, earthen mounded tombs were equipped with various burial goods, including numerous iron weapons and tools. While such iron artifacts are sometimes well-preserved, many of them are recovered as heavily mineralized fragments. In these samples it is difficult to derive useful information concerning their original morphology and chemical composition. To acquire meaningful insights into the technological capabilities and manufacturing practices of specific historical periods and regions, archaeometallurgical research must be grounded in the comprehensive statistical analysis of a substantial number of artifacts. It is therefore important to conduct analysis of as many artifacts as possible. Concerning iron sword blade fragments from Kofun-period mounded tombs, it is often the case that almost no metal survives, then it is usually impossible to obtain detailed compositional or microstructural information. It is nevertheless possible to obtain morphological details provided a technique exists to visualize and spatially map the contrast between the iron-rich minerals derived from the blade corrosion and the surrounding non-metal areas. We performed a test experiment to verify the potential of Neutron Tomography to provide such a contrast within heavily mineralized Kofun-period iron sword fragments from Okayama Prefecture, Japan, with excellent results. Moreover, the combination with Neutron Diffraction and X-ray-based techniques has successfully advanced our interpretation of these archaeological finds in a completely non-invasive way.