CROSS-SECTIONS OF PHOTONUCLEAR REACTIONS ON natМо TARGETS AT END-POINT BREMSSTRAHLUNG ENERGY UP TO Еγmax = 100 МeV

Experiments to determine the yields and bremsstrahlung flux-averaged cross-sections σ(Еγmax) of photonuclear reactions on the natural Mo targets were performed on the beam from the electron linear accelerator LUE-40 with the use of the γ-activation technique. The bremsstrahlung end-point energies were in the range Еγmax = 35…80 MeV. The bremsstrahlung quantum flux was calculated with the program GEANT4.9.2 and, in addition, was monitored using the 100Мо(γ, n)99Мо reaction. Calculations of the yields and average cross-sections σ(Еγmax) for photonuclear reactions on stable Mo isotopes were computed using the σ(Е) cross-sections from the TALYS1.95 code (for the level density model LD1). A comparison of experimental and calculated cross-sections σ(Еγmax) for reactions 92Мо(γ, 2n)90Мо and 92Мо(γ, pn)90Nb was performed.

Supplemental Material: Across-arc variations in Mo isotopes and implications for subducted oceanic crust in the source of back-arc basin volcanic rocks

Sample information, methods, and supplemental figures and tables.<br>

Supplemental Material: Across-arc variations in Mo isotopes and implications for subducted oceanic crust in the source of back-arc basin volcanic rocks

Sample information, methods, and supplemental figures and tables.<br>

Mo mobility in lateritic weathering profiles overlying ultramafic rocks of the East Sulawesi Ophiolite, Indonesia

&lt;p&gt;Molybdenum (Mo) isotopes are known as sensitive recorders for changes in redox conditions because the oxidized form of Mo (Mo VI) is more soluble, whereas its reduced form is more particle reactive. Previous studies suggest that Mo isotopic fractionation during the weathering process is controlled by atmospheric input, Mo host, and bedrock composition. However, Mo isotopic variation and processes influencing fractionation in weathering profiles overlying ultramafic bedrock, the early Earth analog, have yet to be explored. This study explores for the first time (1) Mo behavior and (2) isotopic fractionation in two representative and intensely-weathered lateritic profiles overlying ultramafic bedrock of the East Sulawesi Ophiolite, Indonesia. Mo concentrations measured on samples obtained from laterite successions studied here range between 60 - 537 ppb and are overall higher compared to bedrock values ranging between 9 - 45 ppb. The Mo isotope compositions of laterite samples vary between -0.043&amp;#8240; to -0.161&amp;#8240; &amp;#948;&lt;sup&gt;98&lt;/sup&gt;Mo&lt;sub&gt;NIST3134&lt;/sub&gt;. The overall close to mantle Mo isotopic composition of the laterite samples, their small Mo isotope variability, and the covariation between Mo and Ti concentrations suggest low mobility of Mo during chemical weathering and laterite formation. This low Mo mobility is likely a consequence of a) the low Mo concentration of the ultramafic protolith and b) adsorption of Mo to secondary Fe-Oxides during laterite formation under oxic weathering conditions.&lt;/p&gt;

Molybdenum Isotope Constraints on the Origin of Vanadium Hyper-Enrichments in Ediacaran–Phanerozoic Marine Mudrocks

Vanadium is an important redox-sensitive trace metal for paleoenvironmental reconstructions. Modern organic-rich sediments persistently contain sediment V enrichments <500 μg/g, but many ancient marine organic-rich mudrocks record enrichments >500 μg/g. Previous studies propose that ancient V enrichments of these magnitudes (“V hyper-enrichments”) were deposited from hyper-sulfidic bottom-waters with higher H2S levels (≥10 mM) than observed in modern euxinic basins. To test the importance of hyper-sulfidic conditions for generating V hyper-enrichments, we compare V concentrations with Mo isotope (δ98Mo) compositions from mudrock samples ranging in age from Ediacaran to Pleistocene. In the modern ocean, sediments deposited from strongly euxinic bottom waters ([H2S]aq > 11 μM) closely record global seawater δ98Mo because conversion of molybdate to tri- and tetra-thiomolybdate is quantitative. By contrast, large Mo isotope fractionations occur during Mo adsorption to Fe-Mn particulates or because of incomplete formation of the most sulfidic thiomolybdates in weakly euxinic settings ([H2S]aq < 11 μM), which both favor removal of lighter-mass Mo isotopes to sediments. We find multiple examples when mudrocks with V hyper-enrichments are associated with a wide range of δ98Mo for a single time interval, including values at or below oceanic input δ98Mo (0.3–0.7‰). This observation suggests significant isotopic offset from reasonable seawater values (typically ≥1.0‰). Thus, we conclude that hyper-sulfidic conditions were not responsible for many V hyper-enrichments in Ediacaran–Phanerozoic mudrocks. Instead, sediment V hyper-enrichments can be explained by high Fe-Mn particulate fluxes to weakly euxinic sediments or by moderately restricted euxinic settings with strongly euxinic ([H2S]aq > 11 μM but not necessarily > 10 mM) or weakly euxinic (with slow clastic sedimentation rates and high organic carbon fluxes) bottom waters where vigorous water exchange provides a continuous V supply from the open ocean.

Ratios of negative-to-positive parity level densities in Mo isotopes

The ratios of negative-to-positive parity level densities in ^94,96,98Mo isotopes are calculated using a microscopic formalism based on the BCS model. In this calculation, the single-particle energies are obtained with the Nilsson model. Mass number, shell and deformation effects on the parity equilibration phenomena in these isotopes are discussed in this work.