第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月29日（木） 国立国語研究所 2階講

Fukuoka T.

Kusuno H.

Matsuzaki H.

Miyairi Y.

National Institute of Polar Research Repository

A New Extraction System for Extremely Low Level 14C in Meteorites.  H. Kusuno1, T. Fukuoka1, H. Matsuzaki2 and Y. Miyairi3, 1Graduate school of  Geo-environmental Science, Rissho University, 2School of Engineering, The University of Tokyo, 3Atomspher and Ocean Research Institute, The University of Tokyo.   Introduction: Terrestrial ages of Antarctic meteorites are useful tool to investigate frequency of meteorite falls, pairing of meteorites and accumulation mechanism of meteorites on Antarctic ice sheet. In the Yamato mountain region, more than 13,000 various classes of meteorites have been collected. Terrestrial ages of Yamato meteorites have been known to be concentrated less than 70 kyr compared with those of other site meteorites such as Allan Hills (ALH) meteorites [1, 2, 3]. We determined terrestrial 26Al ages of 47 Yamato HED (howardite, eucrite and diogenite) meteorites. Terrestrial ages of those meteorites distributed from recent to 380 kyr (Kusuno, unpublished data) and 70% of them were less than 70 kyr. We tried determination of 14C (half-life 5730 yr) contents of those Yamato HED meteorites to study distribution of terrestrial ages which showed younger terrestrial ages.  HED meteorites include extremely low level carbon, which is only cosmogenic 14C (saturated 14C amount: 108 atoms/g [4]) because volatile elements including carbon are absent in these meteorites. Therefore the low 14C blank system, which is less than 104 atoms 14C, is required to extract cosmogenic 14C from HED meteorites. Modern atmosphere has 108 atoms of 14C per one litter (modern carbon of 12C/14C ratio = 1.2 *10-12). Therefore the 14C need to be extracted in low pressure system, which is less than 10-1 Pa. Furthermore the extraction system needs furnace which can heat 0.1 – 1 g meteorite samples equally up to 1300 degrees C (melting temperature of Eucrites) with step wised heating, because to recover 100% 14C in HED meteorites, we need to find the release temperature of cosmogenic 14C from HED meteorite samples.  We designed and produced a new simple and compact system for extraction of extremely low level 14C in HED meteorites at Rissho University. This system is able to heat 0.1-1 g meteorite samples equally with step wised heating up to 1500 degrees in less than 10-3 Pa.  Design of the Extraction System: Previous studies extracted cosmogenic gasses from extraterrestrial samples or terrestrial rock (quartz) samples with Radio Frequency (RF) furnace [2, 5], resistance furnace [6, 7] or electrode furnace [8]. RF furnace and electrode furnace are able to be minimized the volume. For RF furnace, however, it is difficult to control temperature and is difficult to heat samples equally. The sample boat of Electrode furnace is often made of Mo or Ta which are high electric resistance. Those metals release carbon [9] and react with carbon. Resistance furnace successfully used for terrestrial quartz samples [7]. We applied resistance furnace to extraction system for extraction 14C in HED meteorites. However, resistance furnace requires large volume for cooling furnace tube. We minimized volume of furnace tubing by application of crucible furnace.  Fig. 1 shows the extraction system of Rissho University. The volume of furnace chamber with high pure alumina tubing is about 250 ml. Pressure of this system reaches less than 1*10-3 Pa at room temperature by vacuum for one hour and reaches the least to 8*10-5 Pa by vacuum for 24 hours.  In our presentation, we will present blank level of the extraction system at the Rissho University and preliminary data for 14C terrestrial ages of HED meteorites.   References: [1] Nishiizumi, K. et al. (1989) Earth Planet. Sci. Lett. 93, 299-313. [2] Jull, A. J. T. et al. (1993) Proc. NIPR Symp. Antarct. Meteor. 6, 374-380. [3] Jull, A. J. T. et al. (1999) Antarct. Meteor. XXIV, 62-63 (abstract). [4] Masarik, J and Reedy, R. (1994) Geochim. Cosmochim. Acta 58, 5307-5317. [5] Minami, M. et al. (2006) MAPS 41, 529-540. [6] Lifton, N. A. et al. (2001) Geochim. Cosmochim. Acta 65, 1953-1969. [7] Pigati, J. S. et al. (2010) Radiocarbon 52, 1236–1243. [8] Bajo, K. et al. (2011) Earth Planets Space 63, 1097-1111. [9] Jull, A. J. T. et al. (1994) NIM B 92, 308-310.      Figure 1. The extremely low level 14C extraction system for HED meteorites at Rissho University 

A New Extraction System for Extremely Low Level 14C in Meteorites.

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A New Extraction System for Extremely Low Level 14C in Meteorites.

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