Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Rb”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Rb(WO3)4 by Materials Project

Rb(WO3)4 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded to twelve O2- atoms to form RbO12 cuboctahedra that share edges with twelve WO6 octahedra and faces with two equivalent RbO12 cuboctahedra. There are eight shorter (3.35 Å) and four longer (3.36 Å) Rb–O bond lengths. In the second Rb1+ site, Rb1+ is bonded to twelve O2- atoms to form RbO12 cuboctahedra that share edges with twelve WO6 octahedra and a faceface with one RbO12 cuboctahedra. There are a spread of Rb–O bond distances ranging from 3.28–3.45 Å. There are four inequivalent W+5.75+ sites. In the first W+5.75+ site, W+5.75+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There are a spread of W–O bond distances ranging from 1.93–1.96 Å. In the second W+5.75+ site, W+5.75+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with two equivalent RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–29°. There are a spread of W–O bond distances ranging from 1.93–1.95 Å. In the third W+5.75+ site, W+5.75+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with three RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There are a spread of W–O bond distances ranging from 1.93–1.95 Å. In the fourth W+5.75+ site, W+5.75+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with three RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There are a spread of W–O bond distances ranging from 1.93–1.97 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.75+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Rb1+ and two W+5.75+ atoms. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.75+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Rb1+ and two W+5.75+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to two W+5.75+ atoms. In the sixth O2- site, O2- is bonded in a linear geometry to two W+5.75+ atoms. In the seventh O2- site, O2- is bonded in a linear geometry to two equivalent W+5.75+ atoms. In the eighth O2- site, O2- is bonded in a linear geometry to two equivalent W+5.75+ atoms. In the ninth O2- site, O2- is bonded in a linear geometry to two equivalent W+5.75+ atoms. In the tenth O2- site, O2- is bonded in a linear geometry to two equivalent W+5.75+ atoms. In the eleventh O2- site, O2- is bonded in a bent 150 degrees geometry to one Rb1+ and two W+5.75+ atoms. In the twelfth O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.75+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rb(WO3)3 by Materials Project

Rb(WO3)3 crystallizes in the monoclinic P2 space group. The structure is three-dimensional. there are two inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded to twelve O2- atoms to form RbO12 cuboctahedra that share edges with twelve WO6 octahedra and faces with two equivalent RbO12 cuboctahedra. There are a spread of Rb–O bond distances ranging from 3.34–3.38 Å. In the second Rb1+ site, Rb1+ is bonded to twelve O2- atoms to form RbO12 cuboctahedra that share edges with twelve WO6 octahedra and faces with two equivalent RbO12 cuboctahedra. There are a spread of Rb–O bond distances ranging from 3.36–3.38 Å. There are six inequivalent W+5.67+ sites. In the first W+5.67+ site, W+5.67+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There is two shorter (1.95 Å) and four longer (2.00 Å) W–O bond length. In the second W+5.67+ site, W+5.67+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There is two shorter (1.92 Å) and four longer (1.95 Å) W–O bond length. In the third W+5.67+ site, W+5.67+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–32°. There is two shorter (1.94 Å) and four longer (2.00 Å) W–O bond length. In the fourth W+5.67+ site, W+5.67+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There is two shorter (1.90 Å) and four longer (1.96 Å) W–O bond length. In the fifth W+5.67+ site, W+5.67+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–32°. There is two shorter (1.92 Å) and four longer (1.95 Å) W–O bond length. In the sixth W+5.67+ site, W+5.67+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six WO6 octahedra and edges with four RbO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–31°. There are a spread of W–O bond distances ranging from 1.90–1.96 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two W+5.67+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two W+5.67+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two W+5.67+ atoms. In the fourth O2- site, O2- is bonded in a linear geometry to two W+5.67+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to two W+5.67+ atoms. In the sixth O2- site, O2- is bonded in a linear geometry to two W+5.67+ atoms. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.67+ atoms. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.67+ atoms. In the ninth O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.67+ atoms. In the tenth O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.67+ atoms. In the eleventh O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.67+ atoms. In the twelfth O2- site, O2- is bonded in a bent 150 degrees geometry to two Rb1+ and two W+5.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Machine learning analysis of RB-TnSeq fitness data predicts functional gene modules in Pseudomonas putida KT2440

ABSTRACT There is growing interest in engineering Pseudomonas putida KT2440 as a microbial chassis for the conversion of renewable and waste-based feedstocks, and metabolic engineering of P. putida relies on the understanding of the functional relationships between genes. In this work, independent component analysis (ICA) was applied to a compendium of existing fitness data from randomly barcoded transposon insertion sequencing (RB-TnSeq) of P. putida KT2440 grown in 179 unique experimental conditions. ICA identified 84 independent groups of genes, which we call fModules (“functional modules”), where gene members displayed shared functional influence in a specific cellular process. This machine learning-based approach both successfully recapitulated previously characterized functional relationships and established hitherto unknown associations between genes. Selected gene members from fModules for hydroxycinnamate metabolism and stress resistance, acetyl coenzyme A assimilation, and nitrogen metabolism were validated with engineered mutants of P. putida . Additionally, functional gene clusters from ICA of RB-TnSeq data sets were compared with regulatory gene clusters from prior ICA of RNAseq data sets to draw connections between gene regulation and function. Because ICA profiles the functional role of several distinct gene networks simultaneously, it can reduce the time required to annotate gene function relative to manual curation of RB-TnSeq data sets. IMPORTANCE This study demonstrates a rapid, automated approach for elucidating functional modules within complex genetic networks. While Pseudomonas putida randomly barcoded transposon insertion sequencing data were used as a proof of concept, this approach is applicable to any organism with existing functional genomics data sets and may serve as a useful tool for many valuable applications, such as guiding metabolic engineering efforts in other microbes or understanding functional relationships between virulence-associated genes in pathogenic microbes. Furthermore, this work demonstrates that comparison of data obtained from independent component analysis of transcriptomics and gene fitness datasets can elucidate regulatory-functional relationships between genes, which may have utility in a variety of applications, such as metabolic modeling, strain engineering, or identification of antimicrobial drug targets.

09 BIOMASS FUELS↗
DOE OSTI2022

ACuZrQ 3 (A = Rb, Cs; Q = S, Se, Te): Direct Bandgap Semiconductors and Metals with Ultralow Thermal Conductivity

ACuZrQ 3 (A = Rb, Cs; Q = S, Se, Te) were synthesized as black platelet crystals. RbCuZrS 3 , RbCuZrSe 3 , and CsCuZrS 3 crystallize in the KCuZrSe 3 structure type with space group Cmcm, and RbCuZrTe 3 and CsCuZrTe 3 crystallize in the lower symmetry space group Pnma. The tellurides exhibit a second order Jahn-Teller distortion with off-centering of Zr in its octahedral environment. The magnitude of the distortion is larger in RbCuZrTe 3 than in CsCuZrTe 3 . The structures of beta-CsCuS 4 and Rb 2 Cu 5 Te 5 were also determined. CsCuZrS 3 melts at 910 C-circle and exhibits partial decomposition upon heating at 275 C-circle, while CsCuZrTe 3 melts incongruently. Our DFT calculations of RbCuZrQ 3 (Q = S, Se) and CsCuZrS 3 indicate direct gap semiconductors in agreement with experiments. ACuZrTe 3 (A = Rb, Cs) were calculated to be metals which was confirmed for RbCuZrTe 3 with variable temperature conductivity measurements and consistent with heat capacity measurements. Spectroscopic measurements found a bandgap and work function of 1.44(5) eV and 4.89(5) eV for RbCuZrS 3 and 0.95(5) eV and 4.67(5) eV for RbCuZrSe 3 , respectively. Finally, RbCuZrTe 3 did not exhibit an optical bandgap and has a work function of 4.64(5) eV. RbCuZrTe 3 exhibits a low thermal conductivity under 0.5 W m -1 K -1 at room temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Colloidal AInSe 2 (A = K, Rb, Cs) Nanocrystals with Tunable Crystal and Band Structures

Wide band gap AInSe 2 (A = K, Rb, Cs) is an important interlayer material for improving the efficiency of Cu(In,Ga)(S,Se) 2 (CIGS) solar cells. Compared to high-vacuum deposition and solid-state synthesis, a less energyintensive method is of interest for its fabrication. Herein, we present the rapid, low-temperature colloidal synthesis of AInSe 2 nanocrystals that opens a pathway for convenient solution processing. The crystal structures and electronic band structures of the nanocrystals were studied, and their particle morphology was found to be dependent on the choice of alkali metal and selenium precursors. Homogeneous solid solution (K,Rb,Cs)InSe 2 nanocrystals were synthesized using a mixture of alkali metal precursors. Their compositions, lattice parameters, and band gaps were easily tuned based on the K:Rb:Cs precursor ratio, providing potential for interface engineering of CIGS nanocrystal-based solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Hyperfine-to-rotational energy transfer in ultracold atom–molecule collisions of Rb and KRb

Energy transfer between different mechanical degrees of freedom in atom–molecule collisions has been studied and largely understood. However, systems involving spins remain less explored. Here, in this study, we directly observed energy transfer from atomic hyperfine to molecular rotation in the 87 Rb ($| {F}_{a},{M}_{{F}_{a}}\rangle =| 2,2\rangle$) + 40 K 87 Rb (X 1 Σ + , rotational state N = 0) ⟶ Rb ($| 1,1\rangle$) + KRb ( N = 0, 1, 2) collision with state-to-state precision. We also performed quantum scattering calculations that rigorously included the coupling between spin and rotational degrees of freedom at short range under the assumption of rigid-rotor KRb monomers moving along a single potential energy surface. The calculated product rotational state distribution deviates from the observations even after extensive tuning of the atom–molecule potential energy surface. In addition, our ab initio calculations indicate that spin–rotation coupling is enhanced close to a conical intersection that is energetically accessible at short range. This, together with the deviation, suggests that vibrational degrees of freedom and conical intersections play an important part in the coupling. Our observations confirm that spin is coupled to mechanical rotation at short range and establish a benchmark for future theoretical studies.

chemical physics↗
DOE OSTI2022

Determination of β -decay feeding patterns of 88 Rb and 88 Kr using the Modular Total Absorption Spectrometer at ORNL HRIBF

We report precise determination of ground-state feeding in the β decay of fission products is an important but challenging component in modeling reactor antineutrino flux and reactor decay heat. The Modular Total Absorption Spectrometer (MTAS) is a versatile NaI(Tl) detector array that determines the true β-decay pattern free from the pandemonium effect, including precise ground-state feeding intensities. In this paper, we report MTAS results of the β feeding intensities of 88 Rb and 88 Kr, fission products with large cumulative yields in nuclear reactors. By comparing MTAS results with previous measurements, 88 Rb provides a validation of MTAS's ability to determine ground-state feedings in β decays, while the precision of 88 Kr ground-state feeding is improved when compared with the Evaluated Nuclear Structure Data File (ENSDF). The investigation of sources that contribute to β feeding branching uncertainties in MTAS experiments is discussed in detail. Lastly, the deconvolution of 88 Rb decay spectra suggests that MTAS can distinguish an allowed β spectral shape from a first forbidden unique β spectral shape.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

CDK4/6 inhibition enhances SHP2 inhibitor efficacy and is dependent upon RB function in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue sarcomas with limited treatment options, and new effective therapeutic strategies are desperately needed. We observe antiproliferative potency of genetic depletion of PTPN11 or pharmacological inhibition using the SHP2 inhibitor (SHP2i) TNO155. Our studies into the signaling response to SHP2i reveal that resistance to TNO155 is partially mediated by reduced RB function, and we therefore test the addition of a CDK4/6 inhibitor (CDK4/6i) to enhance RB activity and improve TNO155 efficacy. In combination, TNO155 attenuates the adaptive response to CDK4/6i, potentiates its antiproliferative effects, and converges on enhancement of RB activity, with greater suppression of cell cycle and inhibitor-of-apoptosis proteins, leading to deeper and more durable antitumor activity in in vitro and in vivo patient-derived models of MPNST, relative to either single agent. Overall, our study provides timely evidence to support the clinical advancement of this combination strategy in patients with MPNST and other tumors driven by loss of NF1.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Wireless Instrumented RB Experiment Preliminary Design and Analysis

The ability to deploy new nuclear fuels for current or future reactor concepts requires carefully designed experiments to generate data to support fuel qualification. Ideally these experiments would include state of-the-art sensing to maximize the amount of in situ data that can be collected during operation. Furthermore, advanced reactor systems can take advantage of integrated in-core sensing technologies to maximize fuel utilization, reduce unnecessary conservativism in design margins, and improve operator’s understanding of limiting peaking factors. Before any novel sensing technologies can be readily adopted for nuclear applications, they must first demonstrate acceptable performance in test reactors. This report summarizes the preliminary design and analysis of the most highly instrumented irradiation experiment ever performed in the removable beryllium (RB) positions of the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The Wireless Instrumented RB Experiment 2021 (WIRE-21) will test a wide range of sensors including wireless sensors being developed by Westinghouse Electric Company (WEC) that could provide in situ measurements of peak fuel temperatures and fuel rod pressurization due to fission gas release. The ability to wirelessly transmit a signal through the fuel rod’s cladding is critical to improving fuel monitoring capabilities without requiring signal penetrations through the cladding pressure boundary, which would significantly impact fuel fabrication, handling, and operation. Other sensors that will be tested in WIRE-21 include an array of thermocouples, self-powered neutron detectors (SPNDs), and spatially distributed fiber-optic temperature sensors. More generally, WIRE-21 will establish a flexible irradiation vehicle design to allow accelerated, economical testing of advanced sensor technologies while leveraging the extremely high neutron flux that is available in HFIR. This report summarizes the mechanical design for WIRE-21, the experimental test matrix, initial neutronic and thermal design analyses, and the active monitoring and control system enhancements necessary to support testing of advanced sensor technologies. The containment for WIRE-21 is similar to previous RB irradiation vehicles but includes a few modifications, most notably the use of integrated compression seals to pass a larger number of sensor leads through the experiment’s pressure boundary. In addition to the sensor leads, inert gas lines are passed into the experiment to enable active temperature control and the ability to pneumatically actuate a bellows-driven pressure sensor. WIRE-21 is targeting temperatures (300–350°C) and neutron fluence levels (~10 22 n/cm 2 ) relevant to light water reactors (LWRs), but the flexible design of the experiment vehicle allows much higher operating temperatures (>1,100°C). Neutronic calculations determine the neutron flux conditions as well as the nuclear heating within the experiments. These results are used as inputs to detailed thermal finite element calculations, which are required to evaluate the complex, three-dimensional heat transfer that occurs within WEC’s wireless sensor enclosures. Initial results show that the temperatures of the sensors’ enclosures and the metal bellows can be operated near the temperature range of LWR coolants and cladding while simultaneously increasing the temperature of a surrogate fuel material to values in the range of 800–1200°C to simulate centerline fuel temperatures during LWR operation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)

Exploratory studies in the systems Rb–Ga–Sn and Cs–Ga–Sn yielded the cubic type-I clathrates with refined compositions Rb8GaxSn46−x and Cs8GaxSn46−x (6.9 < x < 7.5). Nearly single-phase materials with good crystallinity were obtained from stoichiometric reactions of the elements. The structures were characterized by means of single-crystal X-ray diffraction methods. Both Rb8GaxSn46−x and Cs8GaxSn46−x represents cases, where a Group 13 element randomly substitutes a Group 14 element in the structure. The extent of Ga/Sn mixing is apparently governed by the drive of the system to achieve an optimal valence electron count, and hence, Rb8GaxSn46−x and Cs8GaxSn46−x (x ≈ 8) can be regarded as Zintl phases. This notion is supported by structure refinements on a multitude of single-crystal X-ray diffraction data, which also confirm that both types of cages in the cubic type-I structure are fully occupied by Rb and Cs atoms. The open-framework, comprised of 46 nodes per formula unit, adapts to the incorporation of nearly eight Ga atoms within the matrix of Sn, whereby small, short-range distortions result. The exact nature of these effects is still unclear, as so far, the structural variations could only be modeled as both positional and occupational disorder at one of three framework sites. Since vacancies in the structures of the binary type-I clathrates A8Sn46−x☐x (A = Rb, Cs; ☐ = missing Sn atom) are also known to cause local distortions, the latter were also synthesized with the same protocols used for the synthesis of A8GaxSn46−x and structurally re-analyzed. The results from the latter studies confirm that homogeneity issues abound, and that the final structures/compositions are an intricate function of the experimental conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Apollo 14 and 15 samples - Rb-Sr ages, trace elements, and lunar evolution.

Studies concerning Rb-Sr isotopic relations are discussed together with abundance measurements regarding K, Rb, Sr, and Ba in Apollo 14 and 15 rocks and soils. The studies include age determination by the internal isochron technique on one basaltic rock sample from each of the two missions. In addition, total sample measurements have been made on samples of fines material from both missions. Trace element abundances and Rb-Sr systematics in the various grain size fractions of three of the fines have also been analyzed.

Murthy, V. R.↗
NASA NTRS1974

U-Th-Pb and Rb-Sr systematics of Apollo 17 boulder 7 from the North Massif of the Taurus-Littrow valley

Portions of highland breccia boulder 7 collected during the Apollo 17 mission were studied using U-Th-Pb and Rb-Sr systematics. A Rb-Sr internal isochron age of 3.89 plus or minus 0.08 b.y. with an initial Sr-87/Sr-86 of 0.69926 plus or minus 0.00008 was obtained for clast 1 (77135,57) (a troctolitic microbreccia). A troctolitic portion of microbreccia clast 77215,37 yielded a U-Pb internal isochron of 3.8 plus or minus 0.2 b.y. and an initial Pb-206/Pb-207 of 0.69. These internal isochron ages are interpreted as reflecting metamorphic events, probably related to impacts, which reset Rb-Sr and U-Pb mineral systems of older rocks.

Nunes, P. D.↗
NASA NTRS1976

Rb-Sr age of troctolite 76535

Rb-Sr systematics is studied for the lunar troctolite 76535 in phases covering a wide range of Rb and Sr concentrations. A line is obtained corresponding to an age of 4.61 plus or minus 0.07 AE and an initial Sr-87/Sr-86 of 0.69900 plus or minus 0.00003. The Rb-Sr age of 4.55 plus or minus 0.10 AE for the dunite (72417) and that of the troctolite are in approximate agreement and permit an interpretation that these rocks formed during a single major lunar differentiation which presumbly produced an anorthositic-gabbroic lunar crust and layered upper mantle.

Papanastassiou, D. A.↗
NASA NTRS1977

Lunar Rb-Sr chronology

It has been established with the aid of Rb-Sr studies that lunar chronology consists of five episodes, including the formation of the moon approximately 4.6 AE ago (1 AE = 1000 million years), a period of intense bombardment by planetary debris resulting in the formation of the major lunar basins, the end of this period at 3.9-4.0 AE ago, a period of mare flooding extending from 3.9 to 3.2 AE ago, and a relatively quiescent period from 3.2 AE ago to the present. In addition, Rb-Sr-studies have provided valuable constraints on the geochemical evolution of the moon through the determination of the initial Sr-87/Sr-86 ratios which limit the Rb/Sr ratios of the source materials for lunar rocks. Attention is given to the characteristics of the Rb-Sr method, the analytical techniques, the ages of lunar mare basalts, the non-mare rocks, the studies conducted in connection with the various Apollo missions, the lunar cataclysm, lunar soils, and aspects of crustal contamination.

Nyquist, L. E.↗
NASA NTRS1981

Ar-40-Ar-39 and Rb-Sr age determinations on Quaternary volcanic rocks

Ages of leucite and biotite separates from samples of the potassic volcanics of the Roman Comagmatic region are derived by the stepwise degassing variant of the Ar-39-Ar-40 dating method and compared with those derived from Rb-Sr dating in order to evaluate the abilities of the methods to date Quaternary geological events. Six of the leucite separates are found to contain Ar with very high bulk 40/36 ratios and to have well correlated Ar-40 and Ar-39 contents, yielding ages of approximately 338,000 years. Two leucites observed to contain Ar with lower bulk 40/36 ratios and Ar-40/Ar-36 ratios significantly lower than atmospheric are found to have ages in substantial agreement with those of the other leucites despite the uncertainty in the composition of the trapped component. Ages obtained for the biotites are not as precise as those of the leucites, due to difficulties in obtaining a good separation of in situ radiogenic Ar-40 from trapped Ar-40. Ages determined from Rb-Sr measurements for selected tuff samples are found to be in good agreement with the Ar-40-Ar-39 ages of the leucites. Results demonstrate the possibility of attaining precisions of better than 5% in the dating of rocks 350,000 years old by both the Ar-40-Ar-39 and the Rb-Sr methods.

Radicati Di Brozolo, F.↗
NASA NTRS1982

A reexamination of the RB-SR isotopic systematics of lunar breccia 12013

Lunar breccia 12013 is one of the few rocks for which isotopic evidence has been interpreted as indicating a 4.5-AE age, and it is the only lunar rock which contains abundant granitic material that may date back to the initial lunar differentiation. An investigation of 12013 conducted by Quick et al. (1981) has led to the conclusion that 12013 is an extremely complex mixture of impact-generated melt and clastic components of uncertain affinities. It was found that the granitic component in 12013 need not be any older than 4.16-4.17 AE. In the present study a model is presented for the Rb-Sr evolution of 12013 which explains the isotopic data without resorting to a 4.5-AE age for any component. Attention is given to petrographic constraints, isotopic investigations, and an evaluation of the Rb-Sr isotopic data. It is concluded that lunar rock 12013 is an extremely complex polymict breccia in which the Rb-Sr isotopic systematics have been greatly influenced by mixing during breccia formation and by subsequent reequilibration.

Quick, J. E.↗
NASA NTRS1987

Rb-Sr and Sm-Nd systematics of cherts and other siliceous deposits

An analysis of marine and lacustrine cherts demonstrates that Rb-Sr and Sm-Nd systems may be used in elucidating the origin and evolution of cherts, and that the Rb-Sr system may be used for dating. All samples have high Rb/Sr ratios, and though the site of these elements in cherts was not established, they appear to be correlated with Al content. Sm/Nd ratios were typical of continental sources, and the results show the Rb-Sr system in cherts to be isolated from the associated carbonate, with little Sr exchange. Data suggest that in many cases cherts are formed by dissolved SiO2 nucleating on clay-like material which preserves the isotropic characteristics of the detrital source, while in some cases it is possible that cherts were formed from silica-saturated waters from a nonmarine source.

Weis, D.↗