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Apollo 11 lunar rock K, Rb, Sr, Ba and rare earth element concentrations, examining relationship to terrestrial and chondritic levels
Chemical analysis for Li, Na, K, Rb, Cs, Ca, Sr and Ba in achondrites and Apollo 11 lunar rocks, breccia and soil samples
Branching ratios to excited nuclear states formed after muon capture have been measured with Ge(Li) detectors. The delayed gamma rays were observed in studies of muonic Ce-142, Ce-140, Ba-138, and Sn-120, using separated isotopes. The resulting isotopes formed indicate at least a 60% probability of neutron emission upon muon capture, with the most likely product resulting from single-neutron emission. No evidence for delayed proton emission with a probability higher than 2% was found. Using our more precise energies for the observed nuclear transitions, we present revised energy levels schemes for La-141, La-139, Cs-137, and In-119.
Spectra of Cs III, Ba IV, and La V were photographed in a low-voltage sliding spark on a 10.7 m normal-incidence vacuum spectrograph. These ions are isoelectronic with neutral iodine and display a halogen-like energy level structure. Detailed isoelectronic comparisons, level transition diagrams, and tabular data on the transitions of the ions and percentage compositions of Cs III configurations are presented.
Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.
Analyses of whole rock and mineral separates from the Nakhla meteorite are carried out by means of Sm-Nd and U-Tn-Pb systematics and by determining their REE, Ba, Sr, Rb, and K concentrations. Results show that the Sm-Nd age of the meteorite is 1.26 + or - 0.7 b.y., while the high initial epsilon(Nd) value of +16 suggests that Nakhla was derived from a light REE-depleted, old planetary mantle source. A three-stage Sm-Nd evolution model is developed and used in combination with LIL element data and estimated partition coefficients in order to test partial melting and fractional crystallization models and to estimate LIL abundances in a possible Nakhla source. The calculations indicate that partial melting of the source followed by extensive fractional crystallization of the partial melt could account for the REE abundances in the Nakhla constituent minerals. It is concluded that the significantly younger age of Nakhla than the youngest lunar rock, the young differentiation age inferred from U-Th-Pb data, and the estimated LIL abundances suggest that this meteorite may have been derived from a relatively large, well-differentiated planetary body such as Mars.
Differential (in angle) electron scattering experiments on laser-excited Ba-138 1P were carried out at 30- and 100-eV impact energies. The laser light was linearly polarized and located in the scattering plane. The superelastic scattering signal was measured as a function of polarization direction of the laser light with respect to the scattering plane. It was found at low electron scattering angles that the superelastic scattering signal was asymmetric to reflection of the polarization vector with respect to the scattering plane. This is in contradiction with theoretical predictions. An attempt was made to pinpoint the reason for this observation, and a detailed investigation of the influence of experimental conditions on the superelastic scattering was undertaken. No explanation for the asymmetry has as yet been found.
Theoretical calculations of selected excitation energies and oscillator strengths for Ba are presented that overcome the difficulties of previous theoretical treatments. A relativistic effective-core potential treatment is used to account for the relativistic core contraction, but the outermost ten electrons are treated explicitly. Core-valence correlation can be included in this procedure in a rigorous and systematic way through a configuration-interaction calculation. Insight is gained into the importance of relativistic effects by repeating many of the calculations using an all-electron nonrelativistic treatment employing an extended Slater basis set. It is found that the intensity of the intercombination line 3P1-1S0 is accurately determined by accounting for the deviation from LS coupling through spin-orbit mixing with the 1P1 state, and that deviations from the Lande interval rule provide an accurate measure of the degree of mixing.
The critical ionization velocity effect requires a superthermal electron population to ionize through collisional impact. Such superthermal electrons can however lose energy to competing atomic processes, as well as to ionization, thus limiting the efficiency of the effect. Considering Ba and Sr magnetospheric injection experiments designed to test the CIV theory, it is found that in both cases roughly 60 percent of the superthermal electron energy is lost on exciting line radiation. Moreover, energy loss to background neutral oxygen places a strict limit on the injected cloud densities for which critical velocity effects are possible; a finding which explains the consistently negative results in radial injection experiments.
An apparent superconducting transition with an onset temperature above 40 K has been detected under pressure in the La-Ba-Cu-O compound system synthesized directly from a solid-state reaction of La2O3, CuO, and BaCO3 followed by a decomposition of the mixture in a reduced atmosphere. The experiment is described and the results of effects of magnetic field and pressure are discussed.
A stable and reproducible superconductivity transition between 80 and 93 K has been achieved and maintained in a Y-Ba-Cu-O compound system at ambient pressure in a simple liquid-nitrogen Dewar. An upper critical field Hc2(0) estimate of between 80 and 180 T is obtained, and the paramagnetic limiting field at 0 K for a sample with a T(c) of about 90 K is 165 T. It is suggested that the lattice parameters, the valence ratio, and the sample treatments all play a role in achieving superconductivity above 77 K.
X-ray diffraction of La(1.8)Ba(0.2)CuO(4-y) reveals two macroscopically segregated tetragonal (K2NiF4-type) phases of nearly identical lattice parameter. Many peaks show additional broadening upon cooling. This broadening is consistent with a spontaneous monoclinic distortion, with an onset temperature of about 150 K, and is possibly relevant to the superconducting properties. Small single crystals of about 70 micron diameter within the powder aggregate are also studied and show a similar two-phase constituency and a resolvable peak splitting at low temperature.
An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd-Ba-Cu-O superconductor alloy. The GdBa2Cu3O(7-x) phase in the oxygen annealed sample is orthorhombic, while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the 001-line zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.
Measurements of superelastic scattering of electrons by laser-excited Ba-138(...6s6p1P1) atoms were carried out. An asymmetry observed has been explained using a model of scattering from a target with finite dimensions. This model employed coherence parameters which were calculated in the distorted-wave approximation. The results indicated that the interpretation of coherence experiments in terms of scattering from a pointlike target can lead to serious errors in the deduction of coherence parameters at low scattering angles.
A variety of new oxide superconductors were prepared. The crystallographic structures of the oxides were all tetragonal and of the (Ln(+), Ce)4(Ln(+),Ba)4Cu6Oz (Ln(+) = Nd, Sm or Eu) type which had been previously discovered by Akimitsu et al. As the Sr content, y, increased when Ln = Ln(excited state) = Nd, the oxygen content, z, monotonically increased and the superconducting transition temperature, T(sub c), varied exhibiting a maximum. When z was controlled directly by means of high oxygen pressure sintering techniques, T(sub c) was changed accordingly. T(sub c's) of samples with different combinations of Ln and Ln(excited state) and different values of x and y were found to depend on the magnitude of the bond valence sum for a Cu atom located in the bottom plane of the Cu-O5 pyramid. Transport and magnetization measurements were carried out to investigate the magnetic field dependence of superconducting properties and to determine the phenomenological parameters. The Hall coefficients were positive below room temperature and varied yielding a maximum with respect to temperature.
The information available on the BaO(SrO)-NbO-NbO2 system with the niobium atom in the lower oxidation degree is very limited. Very few compounds have been found previously in this system. They are BaNbO3, SrxNbO3(0,7=x=1), Ba2Nb2O9, SrNb8O14; and some suggestions on the BaNb8O14 existence have been made also. At the same time Nb-based oxide compounds could be quite interesting in the search of new noncopper high T(sub c) superconductors Researchers studied Ba(Sr) NbxO2x-2 and Ba2(Sr2)-NbxO2x-1 compositions in the phase diagram of BaO(SrO)-NbO-NbO2 system. The synthesis of the materials was carried out in vacuum at the temperatures of 1000 to 1500 C. Barium carbonate and niobium pentoxide were used as initial components. X-ray analysis was carried out.
Temperature-dependent ultrasonic attenuation measurements have been performed on polycrystalline samples of Tl-Ca-Ba-Cu-O at various frequencies. An attenuation anomaly was observed close to the superconducting transition temperature T(c) (103 K) whose temperature position was frequency-independent. The attenuation decreased exponentially with temperature in the superconducting state for both transverse and longitudinal waves. It was also found that the temperature-dependent sound velocity showed a slope change around T(c).
Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glasss transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder x ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structure transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.