The phases of the Moon : modelling crystallisation of the lunar magma ocean through equilibrium thermodynamics

Funding: TEJ acknowledges support from the State Key Laboratory for Geological Processes and Mineral Resources, China University of Geosciences, Wuhan (Open Fund GPMR201903 ). We thank J. B. Balta and T. Prissel for their challenging reviews that led to significant improvements in the final version.Despite some 50 years of intense research on samples returned from the Apollo missions and lunar meteorites, along with remote-sensing and Earth-based observations, many questions regarding the formation and evolution of the Moon persist. These include the detailed compositional and density structure of the lunar mantle and the source and petrogenesis of the diverse suite of extrusive and intrusive igneous rocks. There is broad agreement that the primary internal structure of the Moon reflects crystallisation of a lunar magma ocean (LMO), and that an inverted density gradient within the mantle cumulates led to some reorganisation of layers by partial convective overturn. Experimental studies have provided invaluable constraints on crystallisation of the LMO, but are limited by the relatively small number of experiments that can practically be undertaken. Here we use recently-developed thermodynamic models for minerals and melt in the K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–TiO2–Cr2O3 system to model crystallisation of a full-moon LMO based on two existing end-member bulk compositions—Taylor Whole-Moon (TWM), and Lunar Primitive Upper Mantle, LPUM—on which many experimental studies have been based. We follow several recent studies in considering equilibrium crystallisation of the first 50 vol.% and fractional crystallisation thereafter. Our results match well with experimental studies, and provide detailed constraints on the major oxide composition, mineralogy and density structure based on the two starting compositions that, while exhibiting some similarities, show important differences. The more fertile TWM composition contains significant quantities of garnet in the deep mantle, whereas the LPUM composition has none. By contrast, prior to any gravitational overturn, the uppermost mantle cumulates for TWM are strongly silica-undersaturated and contain abundant aluminous spinel, whereas those for LPUM are silica-saturated. For both starting compositions, with the exception of TiO2 and Na2O, our modelled compositions of the final dregs of fractionated melt show a reasonable match with existing estimates on the composition of urKREEP. Modelled partial melts of the upper-mantle cumulates at low to moderate melt fractions have major oxide compositions that match well with low- and intermediate-Ti lunar basalts. The correspondence is particularly good for picritic (green) glasses that likely represent melts derived from deeper levels within the upper mantle. The wide spread in TiO2 concentrations in lunar basalts and basaltic glasses is consistent with density-driven reorganisation involving ilmenite. Our simulations provide thermodynamically-robust estimates of the compositional, mineralogical and density structure of the lunar interior that are unprecedented in their detail, and which provide the foundation for several lines of future research addressing the origin and secular evolution of the Moon.PostprintPeer reviewe

Evidence for a change in the nuclear mass surface with the discovery of the most neutron-rich nuclei with 17<Z <25

The results of measurements of the production of neutron-rich nuclei by the fragmentation of a 76-Ge beam are presented. The cross sections were measured for a large range of nuclei including fifteen new isotopes that are the most neutron-rich nuclides of the elements chlorine to manganese (50-Cl, 53-Ar, 55,56-K, 57,58-Ca, 59,60,61-Sc, 62,63-Ti, 65,66-V, 68-Cr, 70-Mn). The enhanced cross sections of several new nuclei relative to a simple thermal evaporation framework, previously shown to describe similar production cross sections, indicates that nuclei in the region around 62-Ti might be more stable than predicted by current mass models and could be an indication of a new island of inversion similar to that centered on 31-Na.Comment: 4 pages, 3 figures, to be published in Physical Review Letters, 200

Novel technique for constraining r-process (n,γ\gamma) reaction rates

A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r-process. As a proof-of-principle, the $\gamma$-spectra from the $\beta$-decay of $^{76}$Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and $\gamma$-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the $^{75}$Ge($n,\gamma$)$^{76}$Ge cross section and reaction rate.Comment: 5 pages, 3 figure

Single shot measurement of a silicon single electron transistor

We have fabricated a custom cryogenic Complementary Metal-Oxide-Semiconductor (CMOS) integrated circuit that has a higher measurement bandwidth compared with conventional room temperature electronics. This allowed implementing single shot operations and observe the real-time evolution of the current of a phosphorous-doped silicon single electron transistor that was irradiated with a microwave pulse. Relaxation times up to 90 us are observed, suggesting the presence of well isolated electron excitations within the device. It is expected that these are associated with long decoherence time and the device may be suitable for quantum information processing

Crack Front Waves and the dynamics of a rapidly moving crack

Crack front waves are localized waves that propagate along the leading edge of a crack. They are generated by the interaction of a crack with a localized material inhomogeneity. We show that front waves are nonlinear entities that transport energy, generate surface structure and lead to localized velocity fluctuations. Their existence locally imparts inertia, which is not incorporated in current theories of fracture, to initially "massless" cracks. This, coupled to crack instabilities, yields both inhomogeneity and scaling behavior within fracture surface structure.Comment: Embedded Latex file including 4 figure

Production cross sections from 82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line

Production cross sections for neutron-rich nuclei from the fragmentation of a 82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 126 neutron-rich isotopes of elements 11 <= Z <= 32 were scanned using an experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 22 <= Z <= 25 (64Ti, 67V, 69Cr, 72Mn). One event was registered consistent with 70Cr, and another one with 75Fe. The production cross sections are correlated with Qg systematics to reveal trends in the data. The results presented here confirm our previous result from a similar measurement using a 76Ge beam, and can be explained with a shell model that predicts a subshell closure at N = 34 around Z = 20. This is demonstrated by systematic trends and calculations with the Abrasion-Ablation model that are sensitive to separation energies.Comment: 13 pages, 11 figures, accepted to Phys.Rev.

Production cross sections of neutron rich isotopes from a 82Se beam

Production cross sections for neutron-rich nuclei from the fragmentation of a 82Se beam at 139 MeV/u were measured. The longitudinal momentum distributions of 122 neutron-rich isotopes of elements $11 \le Z \le 32$ were determined by varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including several isotopes first observed in this work. These are the most neutron-rich nuclides of the elements $22 \le Z \le 25$ (64Ti, 67V, 69Cr, 72Mn). One event was registered consistent with 70Cr, and another one with 75Fe. A one-body Qg systematics is used to describe the production cross sections based on thermal evaporation from excited prefragments. The current results confirm those of our previous experiment with a 76Ge beam: enhanced production cross sections for neutron-rich fragments near Z=20.Comment: Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Design Equation: A Novel Approach to Heteropolymer Design

A novel approach to heteropolymer design is proposed. It is based on the criterion by Kurosky and Deutsch, with which the probability of a target conformation in a conformation space is maximized at low but finite temperature. The key feature of the proposed approach is the use of soft spins (fuzzy monomers) that leads to a design equation, which is an analog of the Boltzmann machine learning equation in the design problem. We implement an algorithm based on the design equation for the generalized HP model on the 3x3x3 cubic lattice and check its performance.Comment: 7 pages, 3 tables, 1 figures, uses jpsj.sty, jpsjbs1.sty, epsf.sty, Submitted to J. Phys. Soc. Jp