Nuclear field shift effects on stable isotope fractionation: a review

Abstract

An anomalous isotope effect exists in many heavy element isotope systems (e.g., Sr, Gd, Zn, U). This effect used to be called the ''odd-even isotope effect'' because the odd mass number isotopes behave differently from the even mass number isotopes. This mass-independent isotope fractionation driving force, which originates from the difference in the ground-state electronic energies caused by differences in nuclear size and shape, is currently denoted as the nuclear field shift effect (NFSE). It is found that the NFSE can drive isotope fractionation of some heavy elements (e.g., Hg, Tl, U) to an astonishing degree, far more than the magnitude caused by the conventional mass-dependent effect (MDE). For light elements, the MDE is the dominant factor in isotope fractionation, while the NFSE is neglectable. Furthermore, the MDE and the NFSE both decrease as temperatures increase, though at different rates. The MDE decreases rapidly with a factor of 1/T 2 , while the NFSE decreases slowly with a factor of 1/T. As a result, even at high temperatures, the NFSE is still significant for many heavy element isotope systems. In this review paper, we begin with an introduction of the basic concept of the NSFE, including its history and recent progress, and follow with the potential implications of the inclusion of the NFSE into the kinetic isotope fractionation effect (KIE) and heavy isotope geochronology.Keywords Isotope fractionation Á Mass-dependent effect Á Nuclear field shift effect Á Mass-independent fractionation Á Nuclear volume effect Á Nuclear shape effect

Origin of the analytical 183W effect and its implications for tungsten isotope analyses

“…42), which is an anomalous isotope effect resulting from differences in nuclear sizes and shapes. [44][45][46] To rst order, this effect scales proportionally to jJ(0)j 2 dhr 2 i, where jJ(0)j 2 is the total electron density at the nucleus and dhr 2 i is the difference in mean-square nuclear charge radii of the respective isotopes. 45,47 As such, a NFS is most signicant for heavy elements (e.g., REEs, U) and, since odd isotopes typically have disproportionately small nuclear charge radii relative to the adjacent even isotopes, 42,46 it is oen accompanied by a diagnostic odd-even isotope fractionation.…”

Drivers of zirconium isotope fractionation in Zr-bearing phases and melts: The roles of vibrational, nuclear field shift and diffusive effects

“…The first-principle calculations presented above quantify mass-dependent isotope fractionations stemming from differences in the vibrational properties of the chemical bonds in Zr isotopologues (Bigeleisen and Mayer, 1947;Urey, 1947), but do not account for the socalled Nuclear Field Shift (NFS) effects, which arise from differences in the volume and shape of atomic nuclei (Bigeleisen, 1996;Knyazev and Myasoedov, 2001;Schauble, 2007;Yang and Liu, 2016). Below, we examine the possibility that NFS could result in significant Zr isotope fractionation at magmatic temperatures.…”

Factors influencing the precision and accuracy of Nd isotope measurements by thermal ionization mass spectrometry

“…In Figure 11, (Cook and Schönbächler, 2016;Fujii et al, 2009;Yang and Liu, 2016), including Nd isotopes during solvent extraction (Fujii et al, 2000) and chromatographic separation on cationexchange resin (Saji et al, 2016;Wakaki and Tanaka, 2012). The nuclear field shift effect is a mass-independent isotope fractionation directly related to the fact that isotopes do not have the same number of neutrons and hence do not share the exact same shape and size of atomic nucleus.…”

“…These nuclear differences are responsible for differences in the zero-point energy levels (i.e. ground-state energy) of the electronic systems that cause the isotopes to behave differently during chemical exchange reactions (see Fujii et al, 2009 andYang andLiu, 2016 for a complete review of the process). In Figure 12, we modeled the theoretical effect of the nuclear field shift for Nd isotopes.…”