Estimation of nuclear volume effect of tungsten isotope fractionation in chemical exchange reaction systems and its application to cosmochemistry.

Abstract

The isotope ratio variation of ¹⁸²W based on the radiometric decay of ¹⁸²Hf has been used to estimate the core formation time of solar system objects. On the other hand, mass-independent isotope fractionation (MIF) has been reported in ¹⁸³W, and the cause of the MIF has not yet been clarified. Therefore, it is important to understand the isotope fractionation mechanism of tungsten in the study of the ¹⁸²Hf-¹⁸²W system. In this study, the ¹⁸²W isotope ratio variation is investigated from the viewpoint of ”isotope effect”, which has not been paid attention so far, and applied to cosmochemistry. Among the isotope effects, we focused on the ”nuclear volume effect” which is one of the factors of MIF. The exact value of 'δr²', the difference of the mean square radius of the nucleus, which is an index to discuss the MIF, has been reported differently in different papers, and the exact 'δr²' is unknown. In this study, we attempted to constrain the 'δr²' by experimentally estimating the MIF due to the nuclear volume effect.