HR: 08:01h
AN: V41E-01 INVITED    [Abstracts]
TI: A Methodology for Absolute Isotope Composition Measurement
AU: * Shen, J J
EM: mountain@earth.sinica.edu.tw
AU: Lee, D
EM: dclee@earth.sinica.edu.tw
AU: Liang, W
EM: wlh@earth.sinica.edu.tw
AB: Double spike technique was a well defined method for isotope composition measurement by TIMS of samples which have natural mass fractionation effect, but it is still a problem to define the isotope composition for double spike itself. In this study, we modified the old double spike technique and found that we could use the modified technique to solve the ¡§true¡¨ isotope composition of double spike itself. According the true isotope composition of double spike, we can measure the absolute isotope composition if the sample has natural fractionation effect. A new vector analytical method has been developed in order to obtain the true isotopic composition of a ⁴²Ca-⁴⁸Ca double spike, and this is achieved by using two different sample-spike mixtures combined with the double spike and the natural Ca data. Because the natural sample, the two mixtures, and the spike should all lie on a single mixing line, we are able to constrain the true isotopic composition of our double spike using this new approach. This method not only can be used in Ca system but also in Ti, Cr, Fe, Ni, Zn, Mo, Ba and Pb systems. The absolute double spike isotopic ratio is important, which can save a lot of time to check different reference standards. Especially for Pb, radiogenic isotope system, the decay systems embodied in three of four naturally occurring isotopes induce difficult to obtain true isotopic ratios for absolute dating.
DE: 1094 Instruments and techniques
DE: 4954 Sea surface temperature
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting