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1. 58 Ni( 3 He,t) 58 Cu*(γ) measurements with GODDESS to constrain the astrophysical rate of 57 Ni(p,γ) 58 Cu

   https://doi.org/10.1088/1742-6596/2586/1/012109  

   Carmichael, S R ; Pain, S D ; Siciliano, M ; Allen, J ; Bardayan, D W ; Boomershine, C ; Campbell, C M ; Carpenter, M P ; Chipps, K A ; Cizewski, J A ; et al ( September 2023 , Journal of Physics: Conference Series)

   The observation ofγrays from the decay of⁴⁴Ti in the remnants of core-collapse supernovae (CCSNe) provides crucial information regarding the nucleosynthesis occurring in these events, as⁴⁴Ti production is sensitive to CCSNe conditions. The final abundance of⁴⁴Ti is also sensitive to specific nuclear input parameters, one of which is the⁵⁷Ni(p,γ)⁵⁸Cu reaction rate. A precise rate for⁵⁷Ni(p,γ)⁵⁸Cu is thus critical if⁴⁴Ti production is to be an effective probe into CCSNe. To experimentally constrain the⁵⁷Ni(p,γ)⁵⁸Cu rate, the structure properties of⁵⁸Cu were measured via the⁵⁸Ni(³He,t)⁵⁸Cu*(γ) reaction using GODDESS (GRETINA ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory’s ATLAS facility. Details of the experiment, ongoing analysis, and plans are presented.

    

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2. Valences of Ti, Cr, and V in Apollo 17 high‐Ti and very low‐Ti basalts and implications for their formation

   https://doi.org/10.1111/maps.13123  

   Simon, Steven B. ; Sutton, Stephen R. ( June 2018 , Meteoritics & Planetary Science)

   To assess the variability of redox states among mare basalt source regions, investigation of the valence of Ti, Cr, and V and the coordination environment of Ti in pyroxene and olivine in lunar rocks viaXANES(X‐ray absorption near‐edge structure) spectroscopy has been extended to Apollo 17 basalts: two high‐Ti (70017 and 74275) hand samples, and three very low‐Ti (70006,371, 70007,289B, and 70007,296) basalt fragments from the Apollo 17 deep drill core. Valences of Ti in pyroxene of both suites range from 3.6 to 4, or from 40% to 0% Ti³⁺, averaging 15–20% Ti³⁺. Assuming Ti³⁺is more compatible in pyroxene than Ti⁴⁺, then even lower Ti³⁺proportions are indicated for the parental melts. TheVLTpyroxene exhibits a slightly wider range of V valences (2.57–2.96) than the high‐Ti pyroxene (2.65–2.86) and a much wider range of Cr valences (2.32–2.80 versus 2.68–2.86); Cr is generally reduced inVLTpyroxene compared to high‐Ti pyroxene. Valences of Ti and Cr inVLTpyroxene become less reduced with increasing FeO contents, possibly indicating change in oxygen fugacity during crystallization. Olivine in all samples has very low (<20%) proportions of Ti³⁺, with no Ti³⁺and higher proportions of Ti in tetrahedral coordination in theVLTs than in the high‐Ti basalts. Olivine in 74275, including that in a dunite clast, has much higher proportions of Cr²⁺than the pyroxene in that sample, consistent with previous studies indicating that the olivine grains in this sample are xenocrysts and possibly indicating oxidation just prior to pyroxene crystallization. Results for this sample, theVLTs, and previously studied Apollo 14 and 15 basalts all indicate that mare magmas were in reducing environments at depth, as recorded in early crystallization products, and that later, presumably shallower environments, were relatively oxidizing; single, characteristicfO₂s of formation cannot be assigned to these samples. A process likely to account for this feature seen in multiple samples is loss by degassing of a reducing, H‐rich vapor (probably H₂) during ascent and/or eruption, causing oxidation of the residual melt, recorded in relatively late‐crystallized pyroxene.

    

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3. New Experimental 23 Na(α, p) 26 Mg Reaction Rate for Massive Star and Type Ia Supernova Models

   https://doi.org/10.3847/1538-4357/abee91  

   Hubbard, N. J. ; Diget, C. Aa. ; Fox, S. P. ; Fynbo, H. O. U. ; Howard, A. M. ; Kirsebom, O. S. ; Laird, A. M. ; Munch, M. ; Parikh, A. ; Pignatari, M. ; et al ( May 2021 , The Astrophysical Journal)

   The²³Na(α,p)²⁶Mg reaction has been identified as having a significant impact on the nucleosynthesis of several nuclei between Ne and Ti in Type Ia supernovae, and of²³Na and²⁶Al in massive stars. The reaction has been subjected to renewed experimental interest recently, motivated by high uncertainties in early experimental data and in the statistical Hauser-Feshbach models used in reaction rate compilations. Early experiments were affected by target deterioration issues and unquantifiable uncertainties. Three new independent measurements instead are utilizing inverse kinematics and Rutherford scattering monitoring to resolve this. In this work we present directly measured angular distributions of the emitted protons to eliminate a discrepancy in the assumptions made in the recent reaction rate measurements, which results in cross sections differing by a factor of 3. We derive a new combined experimental reaction rate for the²³Na(α,p)²⁶Mg reaction with a total uncertainty of 30% at relevant temperatures. Using our new²³Na(α,p)²⁶Mg rate, the²⁶Al and²³Na production uncertainty is reduced to within 8%. In comparison, using the factor of 10 uncertainty previously recommended by the rate compilation STARLIB,²⁶Al and²³Na production was changing by more than a factor of 2. In Type Ia supernova conditions, the impact on production of²³Na is constrained to within 15%.

    

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4. Solvothermal Synthesis of [Cr 7 S 8 (en) 8 Cl 2 ]Cl 3  ⋅ 2H 2 O with Magnetically Frustrated [Cr 7 S 8 ] 5+ Double‐Cubes**

   https://doi.org/10.1002/chem.202103761  

   Gamage, Eranga H. ; Clark, Judith K. ; Yazback, Maher ; Cheng, Hai‐Ping ; Shatruk, Michael ; Kovnir, Kirill ( December 2021 , Chemistry – A European Journal)

   A novel transition metal chalcohalide [Cr₇S₈(en)₈Cl₂]Cl₃ ⋅ 2H₂O, with [Cr₇S₈]⁵⁺dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi‐ and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant,θ=−224(2) K, obtained from Curie‐Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions betweenS=3/2 Cr(III) centers. Due to the complexity of the system with (2S+1)⁷=16384 microstates from seven Cr³⁺centers, a simplified model with only two exchange constants was used for simulations. Density‐functional theory (DFT) calculations yielded the two exchange constants to beJ₁=−21.4 cm⁻¹andJ₂=−30.2 cm⁻¹, confirming competing AFM coupling between the shared Cr³⁺center and the peripheral Cr³⁺ions of the dicubane cluster. The best simulation of the experimental data was obtained withJ₁=−20.0 cm⁻¹andJ₂=−21.0 cm⁻¹, in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr³⁺ions as compared to the AFM exchange between the central and peripheral Cr³⁺ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal‐chalcogenide clusters into polymeric networks.

    

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5. Rare‐earth Metal Substitution in Calcium Germanides with the Tetragonal Cr 5 B 3 Type Structure

   https://doi.org/10.1002/zaac.202200183  

   Suen, Nian‐Tzu ; Bobev, Svilen ( July 2022 , Zeitschrift für anorganische und allgemeine Chemie)

   Calcium germanides with two mid‐late rare‐earth metals, Ca_5−xGd_xGe₃and Ca_5−xTb_xGe₃(x≈0.1−0.2), have been synthesized and structurally characterized. Additionally, a lanthanum‐rich germanide with calcium substitutions, La_5−xCa_xGe₃(x≈0.5) has also been identified. The three structures have been established from single‐crystal X‐ray diffraction methods and confirmed to crystallize with the Cr₅B₃‐type in the tetragonal space groupI4/mcm(no. 140;Z=4; Pearson symboltI32), where part of the germanium atoms are interconnected into Ge₂‐dimers, formally [Ge₂]⁶⁻. Rare‐earth metal and calcium atoms are arranged in distorted trigonal prisms, square‐antiprisms and cubes, centered by Ge or rare‐earth/calcium metal atoms. These studies show that the amount of trivalent rare‐earth metal atoms substituting divalent calcium atoms is in direct correlation with the lengths of the Ge−Ge bond within the Ge₂‐dimers, with distance varying between 2.58 Å in Ca_5−xGd_xGe₃and 2.75 Å in La_5−xCa_xGe₃. Such an elongation of the Ge−Ge bond is consistent with the notion that the parent Ca₅Ge₃Zintl phase (e. g. (Ca²⁺)₅[Ge₂]⁶⁻[Ge⁴⁻]) is being driven out of the ideal valence electron count and further reduced. In this context, this work demonstrates the ability of the germanides with the Cr₅B₃structure type to accommodate substitutions and wider valence electron count while maintaining their global structural integrity.

    

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