| Co-Investigator(Kenkyū-buntansha) |
HIDAKA Hiroshi University of Tokyo, Dept.of Chem., Research Associate, 理学部, 助手 (10208770)
YONEDA Shigekazu Nihon University, Dept.of Chem., Research Associate, 文理学部・化学科, 助手 (60210788)
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| Research Abstract |
It has been judged virtually impossible to confirm directly the current presence of primeval technetium which was formed at the period of nucleosynthesis. Accordingly, efforts were concentrated on detection of extinct primeval Tc. Technetium with Z=43 has two long-lived radioactive isotopes, ^<97>Tc with T_<1/2>=3*10^6y(EC) and ^<98>Tc_<1/2>=4*10^6y(beta^-). Accordingly, from a simple viewpoint of extinct nuclides, the direct approach would be to make high-precision measurement of isotopic compositions of _<44>Ru and _<42>Mo, but in relation with half-life effect and the complex processes of nucleosynthesis around Z=40-44, the isotopic studies on _<40>Zr is also of importance. Chemical separation with high purity of any of trace elements, Ru, Mo and Zr, and subsequent sensitive high-precision mass spectrometry were difficult works to be developed in advance. Based on the studies on isotopic compositions of trace elements in question, the following conclusions were obtained. (1) As for
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Mo, the isotopic variation in terrestrial samples (molybdenites) is small, while the relative variation of isotopic ratios of Mo in iron meteorites refects well the process of nucleosynthesis, in considerably good agreement with the theory. One of the iron meteorites is considered to indicate the effect of extinct ^<97>Tc. (2) Zr from the earth was revealed to keep the isotopic heterogeneity which originates from decays of long-lived Nb isotopes as well as the nucleosynthesis. (3) For Ru, it was the most difficult to develop the method for chemical separation from iron meteorites and the stable sensitive mass spectrometry. Our measurement about ^<98>Ru can be interpreted to indicate the significant effect of ^<98>Tc decay. Taking into account the importance of this result, further improvement in recovery and purification is desired in addition to that in mass spectrometry. Sophisticated computer programming for examination of isotopic aberrations has been developed. Taken altogether, a focal point of extinct technetium has been clarified, which makes promising this subject. As remarkable byproducts from these studies, we succeeded in the following works : (1) geochemical estimation of half-life of double beta decay of ^<96>Zr ; (2) utilization of ^<16>O-enriched oxygen to dispense from the isobaric interferences due to oxygen isotopes ; (3) outstanding improvement of Re-Os dating and of high-precision isotopic measurement of Os. Less
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