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

本研究利用阿高雅大学年代测定与材料研究中心的Tandetron加速器质谱仪，研究了利用铁作催化剂、氢气作还原剂，以CO2为原料制备石墨的高精度放射性碳测年方法中的一些基本问题。当使用石墨化样品时，一次测量所需的碳量减少到1毫克，^&lt；14&gt；C的一西格玛误差为&lt；正负&gt；40年。这证明了样品石墨化对于文化财产的定年是不可或缺的，而可用的样本量相当有限。作为第二步，我们建立了一套程序，通过校正碳样品碳同位素分馏的影响，获得更准确的~(14)C测年。对从每个古代培养样品制备的几种石墨材料进行了重现性测试。试验表明，为了获得高度可靠的结果，14&gt；C测量应重复3次以上。此外，利用主要生长在北美和欧洲的木材样品的树状年代学开发的从14年到历年的校准程序已经成功地应用于日本样品。对一些日本文化财产样品进行了放射性碳测年，如旧纸质文件、文件容器盒、木制雕像、古代铁剑、铁雕像、丝布样品、古代船舶碎片、旧骨骼样品等。通过校准用Tandetron AMS测量的14年和14年，这些样品的日历年与历史估计值一致。放射性碳测年也被证明对辨别仿制品很有用。

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.