International audienceWe report in situ NanoSIMS siderophile minor and trace element abundances in individual Fe-Ni metal grains in the unequilibrated chondrite Krymka (LL3.2). Associated kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of Fe, Ni, Co, Cu, Rh, Ir and Pt. The results show large elemental variations among the metal grains. However, complementary and correlative variations exist between adjacent kamacite-taenite. This is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases. The calculated equilibrium temperature is 446 ± 9 °C. This is concordant with the range given by Kimura et al. (2008) for the Krymka post-accretion thermal metamorphism. Based on Ni diffusivity in taenite, a slow cooling rate is estimated of the Krymka parent body that does not exceed ~1K/Myr, which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites. Elemental ionic radii might have played a role in controlling elemental partitioning between kamacite and taenite. The bulk compositions of the Krymka metal grains have non-solar (mostly subsolar) element/Ni ratios suggesting the Fe-Ni grains could have formed from distinct precursors of non-solar compositions or had their compositions modified subsequent to chondrule formation events
We present our numerical calculations of dielectronic recombination rate coefficients which are spin dependent (2lnl -1snl1 L, 1snl 3 L) and develop scaling relations which are converging for all spin (S), angular (L) and main (n) quantum numbers. The influence of atomic data inaccuracies, spin dependent channelling of dielectronic recombination rates and collisions on the atomic/ionic fractions is discussed.
A general expression for intercombination spontaneous transition probabilities A int in neutral helium is proposed. Consideration of the wavefunction mixing for high n-states showed that interference effects between the upper and lower states lead to a drastic decrease of the transition probabilities for high angular momentum states. This allowed us to develop convergent expressions for A int up to very high principal quantum numbers n. Spin-dependent atomic population kinetics demonstrate the particular influence of interference effects for the singlet/triplet population of high n-states and cascades driven by intercombination transitions.
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