Nuclear field shift effect as a possible cause of Te isotopic anomalies in the early solar system - An alternative explanation of Fehr et al. (2006 and 2009)

Abstract

We explore the possibility that Te isotopic anomalies measured in Ca-Al-rich inclusions (Fehr et al. 2009) and in leachates of carbonaceous chondrites (Fehr et al. 2006) may be due to mass-independent effects controlled by nuclear field shift rather than to nucleosynthetic processes. Fehr et al.'s spectrum of mass-independent anomalies of Te isotopes shows a smooth correlation with mass number and nuclear charge distribution. Ratios of even to odd isotopes, as the 125Te/126Te ratio used by these authors for normalization are particularly prone to nuclear field shift effects. We show that the alternative normalization of isotopic ratios to 130Te/ 126Te strongly reduces the trend of isotopic fractionation with mass number, leaving only 125Te as truly anomalous. For both normalizations (125Te/126Te and 130Te/ 126Te), Fehr et al.'s results fit the theory of Bigeleisen (1996), which suggests that the nuclear field shift effect can potentially account for the observed Te isotope abundances, as an alternative to nucleosynthetic processes. We propose that these mass-independent effects may be acquired during accretion of sulfides from the solar nebula. © The Meteoritical Society, 2009.