Trace element abundances in single presolar silicon carbide grains by synchrotron X-ray fluorescence

详细信息    Trace element abundances in single presolar silicon carbide grains by synchrotron X-ray fluorescence

• 出版日期：2004.
• 页数：1 v. :
• 第一责任说明：Yoav Kashiv.
• 分类号：a342 ; a280
• ISBN：0496836706(ebk.) :

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02h0029751 20120628145331.0 cr un||||||||| 120628s2004 xx ||||f|||d||||||||eng | 3136472 0496836706(ebk.) : CNY371.35 NGL NGL NGL a342 ; a280 Kashiv, Yoav. Trace element abundances in single presolar silicon carbide grains by synchrotron X-ray fluorescence [electronic resource] / Yoav Kashiv. 2004. 1 v. : digital, PDF file. Adviser: Clayton, Robert N. Thesis (Ph.D.)--The University of Chicago, 2004. Synchrotron x-ray fluorescence SXRF) was applied to the study of presolar grains for the first time in this study. 41 single SiC grains of the KJF size fraction mass-weighted median size of 1.86 mum) from the Murchison CM2) Meteorite were analyzed. The absolute abundances of the following elements were determined not every element in every grain): S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Sr, Y, Zr, Nb, Mo, Ru, Os, Ir and Pt underlined elements were detected here for the first time in single grains). There is good agreement between the heavier trace element abundances in the grains and s-process nucleosynthesis calculations. It suggests that smaller 13C pocket sizes are needed in the parent stars, a free parameter in the stellar models, than is deduced from isotopic analyses of s-, and s-mainly, elements, such as Zr and Mo. In addition, the data confirms the radiogenic nature of the Nb in the grains, due to the in situ decay of 93Zr t 1/2 ＝ 1.5 x 106 year). The data suggest that the trace elements condensed into the host SiC grains by a combination of condensation in solid solution and incorporation of subgrains. It seems that many of the trace elements reside mainly in subgrains of two solid solution: 1) a TiC based solid solution, and 2) a Mo-Ru carbide based solid solution. The presence of subgrains of an Fe-Ni alloy solid solution is suggested as well. Subgrains of all 3 solid solutions were observed previously in presolar graphite grains. Cosmic grains. ; Interstellar matter. ; X-ray spectroscopy. ; Fluorescence spectroscopy. Electronic dissertations. aeBook. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=U4eBYdMLXPg%3d NGL Bs1623 rCNY371.35 ; h1 bs1204