A Study on Accurate Radiocarbon Dating of Ancient Cultural Properties with Accelerator Mass Spectrometry

本研究利用国立高雅大学年代测定与材料研究中心的串列加速器质谱仪，以Fe为催化剂，H_2为还原剂，从CO_2中制备石墨，对古代文化财产和文献进行高精度放射性碳年代测定的一些基本问题进行了研究。当使用石墨化的样品时，一次测量所需的碳量减少到1 mg，并且1 μ C的1 σ误差<14>可以追溯到<plus-minus>40年。证明了在样品量有限的情况下，样品石墨化是<14>进行文化遗产^ C测年不可缺少的手段。第二步，我们建立了一个<14>通过校正碳同位素分馏效应获得更精确的碳同位素年龄的方法，并对每个古文化样品中的几种石墨材料进行了还原性测试。试验结果表明，<14>为获得可靠性高的结果，应重复进行3次以上的^ C测量。此外，<14>利用北美和欧洲木材的年轮学，开发了一个从~ 1C年代到日历年的校准程序，并成功地应用于日本的一些文化财产样品，如旧纸质文件、文件容器盒、木制雕像、古代铁剑、铁雕像、丝绸样品、古船碎片、旧骨样品、通过校准Tandetron AMS测量的^ C日期估计的这些样本的日历年<14>与历史估计一致。放射性碳测年也被证明是有用的，以找出仿制品。

This study focussed on some basic problems to attain a high accuracy radiocarbon dating of ancient cultural properties and documents, by using a Tandetron accelerator mass spectrometer of the Dating and Materials Research Center, Ngaoya University.As a first step, a sample preparation method was developed to produce graphite from Co_2, using Fe as a catalyst and H_2 as a reducer. When a graphitized sample is used, carbon amount necessary for one measurement was reduce to 1 mg, and one sigma errors of ^<14>C dates to <plus-minus>40 years. It proved that the sample graphitization is indispensable for ^<14>C dating of cultural properties with rather limited sample amount available. As a second step, we have established a procedure to obtain a more accurate ^<14>C dates by correcting the effect of carbon isotopic fractionation of carbon samples.Repoducibility tests are conducted for several graphite materials prepared from each ancient cultural sample. The tests indicated that ^<14>C measurements should be repeated more than 3 times to get a highly reliable results. In addition, a program for calibration from ^<14>C date to calendar year, developed using dendrochronology of wood samples grown mainly in North America and Europe, has been applied successfully to the Japanese samples.Radiocarbon dating was conducted for some Japanese cultural-property samples, such as old paper documents, document container boxes, wooden statues, ancient iron swords, iron statues, silk cloth samples, ancient ship fragments, old bone samples, etc. The calendar years of those samples, estimated by calibrating the ^<14>C dates measured with a Tandetron AMS,are consistent with historical estimations. The radiocarbon dating is also proved to be useful to figure out imitations.