Radiocarbon dating of historical iron products with accelerator mass spectrometry

Dr Toshio Nakamura1, Mr Koichi Eto2, Mr Takao  Fujimoto3, Mr Tetsuya Yamada4, Prof Tsutomu Saito5, Prof Masayo Minami1

1Nagoya University, Nagoya, Japan, 2Eto Sword Refreshing, Fukuoka, Japan, 3Sword Judgment Expert, Pieter Lodewijk Takstraat, The Neterlands, 4Gangoji Institute for Research of Japanese Property, Minami Hijitsuka, Japan, 5National Institute of Japanese History, Sakura, Japan

The age of ancient iron artifacts can be measured by using carbon component contained in metal iron that was included during the iron producing or iron reprocessing stages. To extract carbon from iron artifacts in a form of CO2, a quartz tube has been used for metal iron combustion at the temperature of 1000°C for about 15 hours. We tested the quartz tube combustion method successfully of metal iron in a fine flake condition of almost 1mm in size. Almost 87 % recovery in average for 24 standard iron material was attained when metal iron weight is about 25% of CuO used as an oxidizer. The CO2 of about 1mg carbon was changed to graphite and 14C dated with the HVE 14C-AMS system at Nagoya University.

One of the famous iron artifacts in Japan is Japanese sword, owned traditionally by samurai, a Japanese warrior, and used during battles. At the present time, Japanese swords are one of excellent art collections, and many fake swords exist in the market. Traditionally, Japanese sword has been authenticated by experts based on visual outlook of them and judged real ones out of fakes. A more scientific method was required for judging the original sword. We have analyzed several iron flakes of about 1mm in size collected from Japanese swords in the course of grinding and re-sharpening them. The analyzed swords were believed to have produced in the 2nd century and after, by the name of the manufacturer inscribed on the surface of the sword, and/or by the traditional judgment by experts. The obtained 14C dates for the sword samples were calibrated with IntCal20 and compared with the authorized production dates by visual analysis. The 14C ages were almost consistent with the judgments. We consider that 14C dating is a useful tool to certificate the visual judgment of the swords by experts and to accept existing historical documents about them.

In addition, iron rust samples are commonly excavated from archeological sites in Japan and in foreign countries. We have tested four rust nail samples form archeological sites in India, to collect carbon component successfully by the quartz tube in the same way as pure metal iron. The nail samples were covered by rust on the surface, but the samples should contain metal portion, because they were attracted by the magnetic filed. The carbon content of the rust nails was from 0.2 to 0.5 % in weight ratio. We are going to get their 14C ages soon.


A Physicist who had been responsible for a Tandetron AMS system from HVEE, at Nagoya University, Japan, for last twenty years.

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Nov 08 - 19 2021