加速器質量分析法による歴史時代資料の¹⁴C年代測定 : 和紙資料の測定を中心に

14C年代測定というと，縄文時代・弥生時代の資料が対象という印象が強いが，加速器質量分析法（AMS）の登場と較正曲線の整備とにより，古文書や古経典など歴史時代の和紙資料についても，14C年代測定を行うことが原理的に可能なものとなるに至った。しかしながら，古文書に限らず，考古学資料や歴史学資料について14C年代測定を行う本来の目的は，その資料が何らかの役割を持った道具として歴史の中に登場した年代を探究するところにあるはずである。14C年代測定によって得られる結果は，歴史学的に意味のある年代そのものではない。この自然科学的年代が，歴史学的年代を明らかにするための情報となりうるかが問題なのである。そこで本研究においては，まずは，書風や奥書・記述内容などから書写年代が判明している古文書・古経典・版本などについて14C年代測定を行った。奈良時代から江戸時代にかけての年代既知資料の測定結果から，和紙はいわゆるold wood effectによる年代のずれが小さく，古文書・古経典の書写年代を判定する上でAMS14C年代が有益な情報の一つとなることが示された。その上で，書写年代の明らかにされていない和紙資料についても14C年代測定を行った。特に古筆切とよばれる古写本の断簡についての測定である。平安・鎌倉時代に書写された物語や家集の写本で，完本の形で現存しているものは極めて稀であるが，こうした断簡の形ではかなりの量が現在まで伝わっている。古筆切は，稀少な写本の内容や筆跡を一部分ながらも伝えるものであり，大変高い史料的価値を有するものである。しかし，古筆切の中には，その美しい筆跡を手本とした後世の臨書や，掛け軸などにするために作製された偽物なども多く含まれている。それゆえ，こうした問題を有する古筆切に焦点をあて，書風・字形・筆勢など書跡史学的な視点に，AMS14C年代測定法という自然科学的視点を加え，書写年代の吟味を行った。When one hears the term carbon-14 dating there is a strong tendency to associate it with materials from the Jomon and Yayoi periods. However, the arrival of the AMS (accelerator mass spectrometry) technique and the establishment of calibration curves has led to the possibility in principle of applying carbon-14 dating to Japanese paper such as old documents and sutras from the historical period. However, the primary objective of carbon-14 dating old documents as well as archaeological materials and historical materials is to uncover the dates when these materials which served as some tool or other appeared in history. Results obtained from carbon-14 dating are not historically significant dates in themselves. The question is whether or not these scientific dates can provide information that will lead to the identification of historical dates.The research detailed here involved the carbon-14 dating of old documents, sutras and woodblock prints for which we know the dates for when they were copied from the style of writing, date inscriptions and contents. The results obtained from taking measurements of materials with known dates ranging from the Nara period through the Edo period revealed that in the case of paper there is minimal discrepancy between dates caused by the so-called old wood effect. Thus, it showed that AMS carbon-14 dating provides a useful source of information for determining the dates for when old documents and sutras were copied. We also took carbon-14 measurements of Japanese paper for which the dates of when they were copied are unknown. In particular, we took measurements of fragments of old copies. These are copies of tales and private poetry anthologies from the Heian and Kamakura periods for which survival of the originals to the present day is extremely scarce, although considerable quantities of them as pieces of manuscript have been passed down to the present day. As pieces of manuscripts with parts of rare content and handwriting they have extremely high historical value. However, these old pieces of manuscript include many later copies made by copying beautiful handwriting and fakes produced for making hanging scrolls. It is for this reason that we investigated the dates for when they were copied focusing on such problematic pieces of manuscripts by adding the scientific method of AMS carbon-14 dating to the method of studying the history of handwriting that considers aspects such as writing styles, character formation and brushstroke pressure