@article{oai:nagoya.repo.nii.ac.jp:00011652, author = {南, 雅代 and Minami, Masayo and 中村, 俊夫 and Nakamura, Toshio}, journal = {名古屋大学加速器質量分析計業績報告書}, month = {Mar}, note = {Terrestrial age of meteorites gives us important informaion to estimate the terrestrial history of the meteorites. With the advent of AMS, the required sample mass of meteorite for measurement has been reduced as small as 0.1g. As a result, many more ^<14>C measurements have been performed intensively by the Toronto AMS group, Canada, the Arizona AMS group, USA, and so on. In Japan, AMS ^<14>C measurements of meteorites have been scarcely performed, to our regret. We have constructed a system to extract carbon from meteorites using a vacuum-tight RF melting method in order to study ^<14>C activities in meteorites, in a similar method used by the Arizona group. A meteorite powder sample mixed with pure iron chips is combusted in a RF furnace (Leco HF-10) in the presence of purified carbon-free oxygen in a closed vacuum-tight glass line system. The sample gases evolved are passed through MnO_2 and Pt/CuO traps, and then the CO_2 is separated in a liq.N_2 trap, by pumping out oxygen completely. The amount of ^<14>CO_2 is determined by a pressure transducer in a certain volume and diluted with a known amount of ^<14>C-free CO_2. The total CO_2 is graphitized by reducing with hydrogen in a Fe-powder catalyst and the produced graphite is measured of its ^<14>C concentration with a Tandetron accelerator mass spectrometer at the Center for Chronological Research, Nagoya University. Terrestrial ^<14>C ages of two Antarctic meteorites, Y-75102 from the Yamato icefield, ALH-77294 and ALH-77262 from the Allan Hills icefield, were determined. The age of Y-75102 is estimated 4.0±1.0 ka, the age of ALH-77294 is 19.5±1.2 ka, and the age of ALH-77262 is 28.5±0.9 ka. The ^<14>C ages on the meteorites roughly agree with the literature value. However, the results of the small-counter method (Fireman, 1983; Fireman and Norris, 1981) tend to be oldest, the results of the AMS method by Jull et al. (1984,1989b, 1998) are youngest, and our results of the AMS method are intermediate. The difference would be caused by analytical uncertainties, contamination in samples, incomplete fusion of samples and back-ground value in the extraction system. Y-74190,Y-75097 and Y-75108,which are thought to have fallen at the same time as Y-75102,gave similar ages of 〜4 ka, though Y-74190 gave a slightly younger age of 2.8 ka. These four chondrites might have fallen at the same time. Further studies are needed to improve analytical technique : reducing back-ground value of the extraction system and complete combustion of meteorites by such as longer heating time in RF furnace and use of much more combustion accelerator. It is indispensable to measure saturated ^<14>C activity of recently fallen meteorites with our extraction system. Furthermore, shielding or depth corrections are needed for ^<14>C terrestrial age determination of a meteorite sample if the meteoroid was very large or very small. We intend to obtan the other radioisotope data such as ^<10>Be to estimate the shielding effect. By normalizing the saturated activity of ^<14>C to that of ^<10>Be in a meteorite, more correct terrestrial age for the meteorite could be obtained., 第13回名古屋大学タンデトロン加速器質量分析計シンポジウム(平成12 (2000)年度)報告 名古屋大学タンデトロン加速器質量分析計第2号機の研究成果と利用計画}, pages = {134--145}, title = {南極隕石の落下<14>^C年代測定}, volume = {12}, year = {2001} }