place: Room851 理学部1号館
time: 2007年5月16日〔水）、5:00 to 7:00 pm
speaker: 藤谷渉
title: Mn-Cr chronology and heterogeneous distribution of Mn and Cr in the
early solar system
abstract：
現在、初期太陽系の様々な年代測定法が考案されているが、それらによって推定さ
れる年代が持つ意味あるいは情報の考察には、それぞれの年代を相互に比較すること
が肝要である。今回のセミナーでは、Ｍｎ−Ｃｒ年代について、データのレビューを
行い、他の年代測定法による年代と比較する。また、Ｍｎ，Ｃｒの同位体比から初期
太陽系におけるＭｎ，Ｃｒ分布の不均一性についても考察する。
place: Room851 理学部1号館
time: 2007年5月29日（火）、5:00 to 7:00 pm
speaker: 伊藤元雄
title: Isotopic measurements of meteorites and Stardust
mission samples with the NanoSIMS 50L
abstract：
The NanoSIMS has become a powerful tool in the field of
cosmochemistry because of its unprecedented combination of
high spatial resolution (〜50nm) and high sensitivity for
isotopic measurements. Coordinated studies by NanoSIMS, TEM
and SEM are also possible, providing simultaneous information
on the mineralogy, and chemical and isotopic compositions in
submicron-scale regions of interest in the materials. The
NanoSIMS has had a major impact on the study of ancient
stardust and molecular cloud materials from meteorites and
interplanetary dust (Messenger et al., 2003; Nguyen and
Zinner, 2004).
Here we have applied the JSC NanoSIMS 50L to studies of the
earliest solar system materials: a Ca, Al-rich inclusion
(CAI) from a meteorite (Ito and Messenger, 2007), and samples
of cometary dust returned by the STARDUST mission
(McKeegan et al., 2006). These materials pose different analytical
challenges: CAIs are comparatively large (0.1-1mm), but have
internal O isotopic variations of 〜5%, conversely cometary dust
is extremely fine grained (0.1-1μm) but rare inclusions have
very large H, O, or N isotopic anomalies (10-50%).
Isotopic imaging was carried out to search for anomalous
isotopic signature in a CAI and in cometary dust.
The measurement procedures are similar to those described in
previous papers for acquiring IMAGEs of 16O-, 17O-, 18O-, 27Al-,
28Si-, and 24Mg16O-in multi-detection with electron multipliers.
We acquired a map of O isotopic distributions of a crystal
boundary between Ti-rich pyroxene and anorthite in
the CAI of Allende meteorite together with an elemental map
of 30Si+/27Al+. A very sharp O isotopic boundary, < 400nm,
between two different mineral phases was found. This O
isotopic boundary exactly follows the crystal boundary
determined by 30Si+/27Al+ elemental map. These results show
that the CAI experienced a rapid cooling following transient
heating when it formed at the early solar system.
The initial studies of cometary dust grains have shown that
large (>10 %) O isotopic anomalies are rare (McKeegan et
al., 2006). However, significant (20-50%) N isotopic
variations on 100 nm scales are observed in fine-grained
carbonaceous materials identified by coordinated TEM analyses.
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