The origin of the terrestrial planets

Three major planets, Venus, Earth, and Mercury formed out of the solar nebula. A fourth planetesimal, Theia, also formed near Earth where it collided in a giant impact, rebounding as the planet Mars. During this impact Earth lost ${\approx}4$\% of its crust and mantle that is now is found on Mars and the Moon. At the antipode of the giant impact, $\approx$60\% of Earth's crust, atmosphere, and a large amount of mantle were ejected into space forming the Moon. The lost crust never reformed and became the Earth's ocean basins. The Theia impact site corresponds to Indian Ocean gravitational anomaly on Earth and the Hellas basin on Mars. The dynamics of the giant impact are consistent with the rotational rates and axial tilts of both Earth and Mars. The giant impact removed sufficient CO$_2$ from Earth's atmosphere to avoid a runaway greenhouse effect, initiated plate tectonics, and gave life time to form near geothermal vents at the continental margins. Mercury formed near Venus where on a close approach it was slingshot into the Sun's convective zone losing 94\% of its mass, much of which remains there today. Black carbon, from CO$_2$ decomposed by the intense heat, is still found on the surface of Mercury. Arriving at 616 km/s, Mercury dramatically altered the Sun's rotational energy, explaining both its anomalously slow rotation rate and axial tilt. These results are quantitatively supported by mass balances, the current locations of the terrestrial planets, and the orientations of their major orbital axes

Evidence against correlations between nuclear decay rates and Earth-Sun distance

We have reexamined our previously published data to search for evidence of correlations between the rates for the alpha, beta-minus, beta-plus, and electron-capture decays of 22Na, 44Ti, 108Agm, 121Snm, 133Ba, and 241Am and the Earth-Sun distance. We find no evidence for such correlations and set limits on the possible amplitudes of such correlations substantially smaller than those observed in previous experiments

Measurement of the Hyperfine Structure and Isotope Shifts of the 3s23p2 3P2 to 3s3p3 3Do3 Transition in Silicon

The hyperfine structure and isotope shifts of the 3s23p2 3P2 to 3s3p3 3Do3 transition in silicon have been measured. The transition at 221.7 nm was studied by laser induced fluorescence in an atomic Si beam. For 29Si, the hyperfine A constant for the 3s23p2 3P2 level was determined to be -160.1+-1.3 MHz (1 sigma error), and the A constant for the 3s3p3 3Do3 level is -532.9+-0.6 MHz. This is the first time that these constants were measured. The isotope shifts (relative to the abundant isotope 28Si) of the transition were determined to be 1753.3+-1.1 MHz for 29Si and 3359.9+-0.6 MHz for 30Si. This is an improvement by about two orders of magnitude over a previous measurement. From these results we are able to predict the hyperfine structure and isotope shift of the radioactive 31Si atom, which is of interest in building a scalable quantum computer

Summary Report: First Research Coordination Meeting on ReferenceDatabase for Neutron Activation Analysis

Potential problems associated with nuclear data for neutronactivation analysis were identified, the scope of the work to beundertaken was defined together with its priorities, and tasks wereassigned to participants. Data testing and measurements refer to gammaspectrum peak evaluations, detector efficiency calibration, neutronspectrum characteristics and reference materials analysis

Measurement of actinide neutron cross sections

The maintenance of strong scientific expertise is criticalto the U.S. nuclear attribution community. It is particularly importantto train students in actinide chemistry and physics. Neutroncross-section data are vital components to strategies for detectingexplosives and fissile materials, and these measurements requireexpertise in chemical separations, actinide target preparation, nuclearspectroscopy, and analytical chemistry. At the University of California,Berkeley and the Lawrence Berkeley National Laboratory we have trainedstudents in actinide chemistry for many years. LBNL is a leader innuclear data and has published the Table of Isotopes for over 60 years.Recently, LBNL led an international collaboration to measure thermalneutron capture radiative cross sections and prepared the EvaluatedGamma-ray Activation File (EGAF) in collaboration with the IAEA. Thisfile of 35,000 prompt and delayed gamma ray cross-sections for allelements from Z=1-92 is essential for the neutron interrogation ofnuclear materials. LBNL has also developed new, high flux neutrongenerators and recently opened a 1010 n/s D+D neutron generatorexperimental facility

Prompt gamma activation analysis (PGAA) and short-lived neutron activation analysis (NAA) applied to the characterization of legacy materials

Without quality historical records that provide the composition of legacy materials, the elemental and/or chemical characterization of such materials requires a manual analytical strategy that may expose the analyst to unknown toxicological hazards. In addition, much of the existing legacy inventory also incorporates radioactivity, and, although radiological composition may be determined by various nuclear-analytical methods, most importantly, gamma-spectroscopy, current methods of chemical characterization still require direct sample manipulation, thereby presenting special problems with broad implications for both the analyst and the environment. Alternately, prompt gamma activation analysis (PGAA) provides a'single-shot' in-situ, non-destructive method that provides a complete assay of all major entrained elemental constituents.1-3. Additionally, neutron activation analysis (NAA) using short-lived activation products complements PGAA and is especially useful when NAA activation surpasses the PGAA in elemental sensitivity

Analyses of Oxyanion Materials by Prompt Gamma Activation Analysis

Prompt gamma activation analysis (PGAA) has been used to analyze metal ion oxyanion materials that have multiple applications, including medicine, materials, catalysts, and electronics. The significance for the need for accurate, highly sensitive analyses for the materials is discussed in the context of quality control of end products containing the parent element in each material. Applications of the analytical data for input to models and theoretical calculations related to the electronic and other properties of the materials are discussed

Impact-related microspherules in Late Pleistocene Alaskan and Yukon “muck” deposits signify recurrent episodes of catastrophic emplacement

Large quantities of impact-related microspherules have been found in fine-grained sediments retained within seven out of nine, radiocarbon-dated, Late Pleistocene mammoth (Mammuthus primigenius) and bison (Bison priscus) skull fragments. The well-preserved fossils were recovered from frozen “muck” deposits (organic-rich silt) exposed within the Fairbanks and Klondike mining districts of Alaska, USA, and the Yukon Territory, Canada. In addition, elevated platinum abundances were found in sediment analysed from three out of four fossil skulls. In view of this new evidence, the mucks and their well-preserved but highly disrupted and damaged vertebrate and botanical remains are reinterpreted in part as blast deposits that resulted from several episodes of airbursts and ground/ice impacts within the northern hemisphere during Late Pleistocene time (~46–11 ka B.P.). Such a scenario might be explained by encounters with cometary debris in Earth-crossing orbits (Taurid Complex) that was generated by fragmentation of a large short-period comet within the inner Solar System

SeaWiFS Technical Report Series

Two issues regarding primary productivity, as it pertains to the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Program and the National Aeronautics and Space Administration (NASA) Mission to Planet Earth (MTPE) are presented in this volume. Chapter 1 describes the development of a science plan for deriving primary production for the world ocean using satellite measurements, by the Ocean Primary Productivity Working Group (OPPWG). Chapter 2 presents discussions by the same group, of algorithm classification, algorithm parameterization and data availability, algorithm testing and validation, and the benefits of a consensus primary productivity algorithm