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NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are “ground truth” for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in the DLC. The resulting SW Mg fractionation relative to the DSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (total) error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. (2011).

Solar abundances are important to planetary science since the prevalent model assumes that the composition of the solar photosphere is that of the solar nebula from which planetary materials formed. Thus, solar abundances are a baseline for planetary science. Previously, solar abundances have only been available through spectroscopy or by proxy (CI). The Genesis spacecraft collected and returned samples of the solar wind for laboratory analyses. Elemental and isotopic abundances in solar wind from Genesis samples have been successfully measured despite the crash of the re‐entry capsule. Here we present science rationales for a set of 12 important (and feasible postcrash) Science and Measurement Objectives as goals for the future (Table 1). We also review progress in Genesis sample analyses since the last major review (Burnett 2013). Considerable progress has been made toward understanding elemental fractionation during the extraction of the solar wind from the photosphere, a necessary step in determining true solar abundances from solar wind composition. The suitability of Genesis collectors for specific analyses is also assessed. Thus far, the prevalent model remains viable despite large isotopic variations in a number of volatile elements, but its validity and limitations can be further checked by several Objectives.

We compare element and isotopic fractionations measured in solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are consistent with the process of solar wind fractionation. Based on bulk wind measurements, we also consider in more detail the isotopic and elemental abundances of O. We find mild support for an O abundance in the range 8.75 - 8.83, with a value as low as 8.69 disfavored. A stronger conclusion must await solar wind regime specific measurements from the Genesis samples., Comment: 6 pages, accepted by Astrophysical Journal Letters

An amorphous diamond-like carbon film deposited on silicon made at Sandia National Laboratory by pulsed laser deposition was one of several solar wind (SW) collectors used by the Genesis Mission (NASA Discovery Class Mission #5). The film was ~1 μm thick, amorphous, anhydrous, and had a high ratio of sp 3–sp 2 bonds (>50%). For 27 months of exposure to space at the first Lagrange point, the collectors were passively irradiated with SW (H fluence ~2 × 1016 ions cm−2; He fluence ~8 × 1014 ions cm−2). The radiation damage caused by the implanted H ions peaked at 12–14 nm below the surface of the film and that of He about 20–23 nm. To enable quantitative measurement of the SW fluences by secondary ion mass spectroscopy, minor isotopes of Mg (25Mg and 26Mg) were commercially implanted into flight-spare collectors at 75 keV and a fluence of 1 × 1014 ions cm−2. The shapes of analytical depth profiles, the rate at which the profiles were sputtered by a given beam current, and the intensity of ion yields are used to characterize the structure of the material in small areas (~200 × 200 ± 50 μm). Data were consistent with the hypothesis that minor structural changes in the film were induced by SW exposure. Electronic supplementary material The online version of this article (doi:10.1007/s10853-017-1267-3) contains supplementary material, which is available to authorized users.

The Genesis Discovery mission returned solar matter in the form of the solar wind with the goal of obtaining precise solar isotopic abundances (for the first time) and greatly improved elemental abundances. Measurements of the light noble gases in regime samples demonstrate that isotopes are fractionated in the solar wind relative to the solar photosphere. Theory is required for correction. Measurement of the solar wind O and N isotopes shows that these are very different from any inner solar system materials. The solar O isotopic composition is consistent with photochemical self-shielding. For unknown reasons, the solar N isotopic composition is much lighter than essentially all other known solar system materials, except the atmosphere of Jupiter. Ne depth profiling on Genesis materials has demonstrated that Ne isotopic variations in lunar samples are due to isotopic fractionation during implantation without appealing to higher energy solar particles. Genesis provides a precise measurement of the isotopic differences of Ar between the solar wind and the terrestrial atmosphere. The Genesis isotopic compositions of Kr and Xe agree with data from lunar ilmenite separates, showing that lunar processes have not affected the ilmenite data and that solar wind composition has not changed on 100 Ma time scales. Relative to Genesis solar wind, ArKrXe in Q (the chondrite noble gas carrier) and the terrestrial atmosphere show relatively large light isotope depletions.

The Genesis mission sampled solar wind ions to document the elemental and isotopic compositions of the Sun and, by inference, of the protosolar nebula. Nitrogen was a key target element because the extent and origin of its isotopic variations in solar system materials remain unknown. Isotopic analysis of a Genesis Solar Wind Concentrator target material shows that implanted solar wind nitrogen has a ^(15)N/^(14)N ratio of 2.18 ± 0.02 × 10^(−3) (that is, ≈40% poorer in ^(15)N relative to terrestrial atmosphere). The ^(15)N/^(14)N ratio of the protosolar nebula was 2.27 ± 0.03 × 10^(−3), which is the lowest ^(15)N/^(14)N ratio known for solar system objects. This result demonstrates the extreme nitrogen isotopic heterogeneity of the nascent solar system and accounts for the ^(15)N-depleted components observed in solar system reservoirs.

Minor element variations in MgAl_2O_4 spinel from the type B1 calcium-aluminum-rich inclusion (CAI) Allende TS-34 confirm earlier studies in showing correlations between the minor element chemistry of spinels with their location within the inclusion and with the chemistry of host silicate phases. These correlations result from a combination of crystallization of a liquid produced by re-melting event(s) and local re-equilibration during subsolidus reheating. The correlation of the Ti and V in spinel inclusions with the Ti and V in the adjacent host clinopyroxene can be qualitatively explained by spinel and clinopyroxene crystallization prior to melilite, following a partial melting event. There are, however, difficulties in quantitative modeling of the observed trends, and it is easier to explain the Ti correlation in terms of complete re-equilibration. The correlation of V in spinel inclusions with that in the adjacent host clinopyroxene also cannot be quantitatively modeled by fractional crystallization of the liquid produced by re-melting, but it can be explained by partial re-equilibration. The distinct V and Ti concentrations in spinel inclusions in melilite from the edge regions of the CAI are best explained as being affected by only a minor degree of re-equilibration. The center melilites and included spinels formed during crystallization of the liquid produced by re-melting, while the edge melilites and included spinels are primary. The oxygen isotope compositions of TS-34 spinels are uniformly ^(16)O-rich, regardless of the host silicate phase or its location within the inclusion. Similar to other type B1 CAIs, clinopyroxene is ^(16)O-rich, but melilite is relatively ^(16)O-poor. These data require that the oxygen isotope exchange in TS-34 melilite occurred subsequent to the last re-melting event.

We present detailed simulations of the optical spectra emitted from an argon plasma whose conditions correspond to those thought to prevail within sonoluminescing bubbles. The model incorporates detailed atomic physics based on atomic data from the Opacity Project database, and includes bound-bound, bound-free and free-free transitions. Line broadening is treated using the modified semi-empirical method. The spectral model is used as a postprocessor of hydrodynamic simulations. While finding excellent agreement with the shape of experimental spectra, we calculate an intensity that is a factor of 100 greater than that in experiment. We also predict that whilst the majority of the optical emission corresponds to bound-free transitions, there remains the possibility of observing broad line emission in both the UV and IR regions of the spectrum.

Isotope dilution thorium and uranium analyses by inductively-coupled plasma mass spectrometry of 12 samples of Harleton (L6) show a much larger scatter than was previously observed in equilibrated ordinary chondrites. Th/U linearly correlates with 1/U in Harleton and in the total equilibrated ordinary chondrite data set as well. Such a correlation suggests a two component mixture and this trend can be quantitatively modeled as reflecting variations in the mixing ratio between two phosphate phases: chlorapatite and merrillite. The major effect is due to apatite variations, which strongly control the whole rock U concentrations. Phosphorous variations will tend to destroy the Th/U vs. 1/U correlation, and measured P concentrations on exactly the same samples as U and Th show a factor of 3 range. It appears that the P variations are compensated by inverse variations in U (a dilution effect) to preserve the Th/U vs. 1/U correlation. Because variations in whole rock Th/U are consequences of phosphate sampling, a weighted average of high accuracy Th/U measurements in equilibrated ordinary chondrites should converge to a significantly improved average solar system Th/U. Our best estimate of this ratio is 3.53 with σ_(mean) = 0.10.

We have conducted an electron microprobe study of minor element distributions among spinels from two type B1 calcium-aluminum-rich inclusions (CAIs): Allende TS-23 and Leoville 3537–2. We show that by maintaining the petrologic context (edge, middle, and center of the inclusion plus their host silicate phase), four populations of spinels are resolvable based on their minor element contents. One population resides within the edge area (mainly mantle melilite) and is characterized by the highest V contents. Unlike Leoville 3537–2, many edge grains from Allende TS-23 also have high-Fe contents (up to 4.0 wt%) and low-Cr values. Based on their V and Ti concentrations (which is positively correlated), middle and center grains define a trend that is divided into three populations: spinels enclosed by melilite, fassaite, and anorthite. The overall range in Ti concentration based on fractional crystallization should be much less than a factor of 2; however, the observed range is considerably larger. The minor element contents of these grains are interpreted as recording alteration, primary fractional crystallization, and a complex igneous history that may involve remelting and recrystallization. From our data, Allende TS-23 has experienced more alteration than Leoville 3537–2, which is consistent with previous petrologic studies of silicates within these objects; yet both objects have likely been remelted (at least one additional melting event, possibly two, postdating the initial formation of these CAIs). By invoking a remelting history, the large range ir Ti concentrations and the different populations of spinels can be explained. Although our data suggest that more than one generation of spinels exist within these objects, we are unable to establish any population of relic spinel grains that predate the initial melting event.

We present the results of time-resolved interferometric measurements of the electron-density profile in a discharge-ablated capillary waveguide. We observe the development of a pronounced axial minimum in the electron-density profile with a relative depth of as much as 60% of the axial electron density. Such a profile is suitable for channeling high-intensity laser pulses.

It has been proposed that the composition of the solar wind could be measured directly by transporting ultrapure collectors into space, exposing them to the solar wind, and returning them to earth for analysis. In a study to help assess the applicability of present and future postionization secondary neutral mass spectrometers for measuring solar wind implanted samples, measurements of Zr in Si were performed. A three-color resonant ionization scheme proved to be efficient while producing a background count rate limited by secondary ion signal (5×10^(−4) counts/laser pulse). This lowered the detection limit for these measurements to below 500 ppt for 450,000 averages. Unexpectedly, the Zr concentration in the Si was measured to be over 4 ppb, well above the detection limit of the analysis. This high concentration is thought to result from contamination during sample preparation, since a series of tests were performed that rule out memory effects during the analysis.

The combination of secondary neutral mass spectrometry (SNMS) and resonance ionization spectroscopy (RIS) has been shown to be a powerful tool for the detection of low levels of elemental impurities in solids. Drawbacks of the technique have been the laser-repetition-rate-limited, low duty cycle of the analysis and the fact that RIS schemes are limited to determinations of a single element. These problems have been addressed as part of an ongoing program to explore the usefulness of RIS/SNMS instruments for the analysis of naturally occurring samples. Efficient two-color, two-photon (1+1) resonance ionization schemes were identified for Mo and for four platinum-group elements (Ru, Os, Ir, and Re). Careful selection of the ionization schemes allowed Mo or Ru to be measured simultaneously with Re, Os, or Ir, using two tunable dye lasers and an XeCl excimer laser. Resonance frequencies could be switched easily under computer control, so that all five elements can be rapidly analyzed. In situ measurements of these elements in metal grains from five meteorites were conducted. From the analyses, estimates of the precision and the detection limit of the instrument were made. The trade-off between lower detection limits and rapid multielement RIS analyses is discussed.

We heated mixtures of sulfur and Na-bearing silicates in evacuated silica glass capsules to temperatures between 600°C and 950°C. At or above 850°C, Na-silicate glass reacts with elemental S to form a (Na,K) sulfide. Mobilization of this phase may account for the presence of Na and K on the surface of Io, and hence in the material sputtered into the Jovian magnetosphere.

A general review of lunar science is presented, utilizing two themes: a summary of fundamental problems relating to the composition, structure, and history of the moon and a discussion of some surprising, unanticipated results obtained from Apollo lunar science. (1) The moon has a crust of approximately 60-km thickness, probably composed of feldspar-rich rocks. Such rocks are exposed at the surface in the light-colored lunar highlands. Many highlands rocks are complex impact breccias, perhaps produced by large basin-forming impacts. Most highlands rocks have ages of ∼3.9 × 10^9 yr; the record of igneous activity at older times is obscured by the intense bombardment. The impact rate decreased sharply at 3.8–3.9 × 10^9 yr ago. The impact basins were filled by flows of Fe- and, locally, Ti-rich volcanic rocks creating the dark mare regions and providing the strong visual color contrast of the moon, as viewed from earth. Crustal formation has produced enrichments in many elements, e.g., Ba, Sr, rare earths, and U, analogous to terrestrial crustal rocks. Compared with these elements, relatively volatile elements like Na, K, Rb, and Pb are highly depleted in the source regions for lunar surface rocks. These source regions were also separated from a metal phase, probably before being incorporated into the moon. The physical properties of the lunar mantle are compatible with mixtures of olvine and pyroxene, although Ca- and Al-rich compositions cannot be ruled out. Deeper regions, below ∼1000 km, are probably partially molten. (2) Lunar rocks cooled in the presence of a magnetic field very much stronger than the one that exists today, owing either to dynamo action in an ancient molten core or to an external magnetization of the moon. Lunar soil properties cannot be explained strictly by broken-up local rocks. Distant impacts throw in exotic material from other parts of the moon. About 1% of the soil appears to be of meteoritic origin. Vertical mixing by impacts is important; essentially all material sampled from lunar cores shows evidence of surface residence. The surface layers of lunar material exposed to space contain a chemical record of implanted solar material (rare gases, H) and constituents of a lunar atmosphere (^(40)Ar, Pb). Large isotopic fractionation effects for O, Si, S, and K are present. Physical properties of the surface layers are dominated by radiation damage effects. Lunar rocks have impact craters (≤1 cm) produced by microgram-sized interplanetary particles. The contemporary micrometeorite flux may be much higher than is indicated by the microcrater densities, indicating time variations in the flux. Particle track studies on the returned Surveyor camera filter first showed that the Fe nuclei were preferentially enhanced in solar flares.

A nuclear microprobe cannot give direct information on the chemical state of an element, but the spatial distribution of elements in a specimen is often determined by the chemical history of the sample. Fuel cells and minerals are examples of complex systems whose elemental distributions are determined by past chemical history. The distribution of catalyst in used fuel cell electrodes provides direct information on the chemical stability of dispersed catalysts under operating conditions. We have used spatially resolved Rutherford backscattering to measure the migration of platinum and vanadium from intermetallic catalysts and to determine their suitability for use under the extreme operating conditions found in phosphoric acid fuel cells. Geologic materials are complex, heterogeneous samples with small mineral grains. The trace element distribution within the individual mineral grains and between different mineral phases is sensitive to the details of the mineral formation and history. The spatial resolution and sub-100-ppm sensitivity available with a nuclear microprobe open up several new classes of experiments to the geochemist. Geochemistry and electrochemistry are two areas proving particularly fruitful for application of the nuclear microprobe.

The possibility of heating of planetary cores by K radioactivity has been extensively discussed, as well as the possibility that K partitioning into the terrestrial core is the reason for the difference between the terrestrial and chondritic K/U. We had previously suggested that U and Th partitioning into FeFeS liquids was more important than K. Laboratory FeFeS liquid, silicate liquid partition coefficient measurements (D) for K, U, and Th were made to test this suggestion. For a basaltic liquid at 1450°C and 1.5 GPa, D_U is 0.013 and D_K is 0.0026; thus U partitioning into FeFeS liquids is 5 times greater than K partitioning under these conditions. There are problems with 1-atm experiments in that they do not appear to equilibrate or reverse. However, measurable U and Th partitioning into sulfide was nearly always observed, but K partitioning was normally not observed (D_K ≲ 10^(−4)). A typical value for D_U from a granitic silicate liquid at one atmosphere, 1150°C, and low f0_2 is about 0.02; D_(Th) is similar. At low f0_2 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with D_U > 1. D_(Th) is less strongly affected. Because of the consistently low D_K/D_U, pressure effects near the core-mantle boundary would need to increase D_U by factors of ∼10^3 with much smaller increases in DU in order to have the terrestrial K and U abundances at chondritic levels. In addition, if radioactive heating is important for planetary cores, U and Th will be more important than K unless the lower mantle has K/U greater than 10 times chondritic or large changes in partition coefficients with conditions reverse the relative importance of K versus U and Th from our measurements.

In the Hvittis enstatite chondrite fission track radiography shows that U is highly concentrated in CaS (oldhamite), with a concentration of 400±50 ppb. The oldhamite U concentrations are equilibrated, although intergrain concentration variations of less than 15% would not be detected. Various approaches to a U material balance do not agree, but at least 50% and, more likely, nearly 100% of the U is concentrated in CaS. It is likely that CaS is the major reservoir for other actinide and lanthanide elements as well. Consequently, enstatite chondrites may provide reliable Pu/U abundance ratios. The highly reducing formation conditions for enstatite chondrites have caused U to deviate from lithophile behaviour, but K is observed to remain lithophile. Although this observation may not be generalizable, we propose that discussions of radioactive heating of planetary cores should include U and Th and not focus exclusively on K.

The isotopic composition of Gd in one chondrite, two achondrites and the silicate inclusions of two meteorites have been determined. When corrected for mass discrimination, Gd in all samples except the Norton County achondrite shows the same relative isotopic abundances as terrestrial Gd. These results set an upper limit of 3 × 10 15 neutrons per cm 2 on a differential integrated thermal neutron irradiation of the earth and these meteorites. Neutron capture effects are present in Gd extracted from the Norton County achondrite. These most probably have been produced by secondary neutrons during the exceptionally long cosmic ray exposure of this large stone meteorite. The isotopic anomalies correspond to an integrated thermal neutron flux of (6.3 ± 0.9) × 10 15 neutrons per cm 2 .

The isotopic composition of Gd in one chondrite, two achondrites, and the silicate inclusions of two iron meteorites has been determined. When corrected for mass discrimination, Gd in all samples except the Norton County achondrite shows the same relative isotopic abundances as terrestrial Gd. These results set an upper limit of 3×10^(15) neutrons per cm^2 on a differential integrated thermal neutron irradiation of the earth and these meteorites. Neutron-capture effects are present in Gd extracted from the Norton County achondrite. These most probably have been produced by secondary neutrons during the exceptionally long cosmic ray exposure of this large stone meteorite. The isotopic anomalies correspond to an integrated thermal neutron flux of (6.3±0.9)×10^(15) neutrons per cm^2. The percent abundances of terrestrial Gd found in our work for Gd^(160), Gd^(158), Gd^(157), Gd^(156), Gd^(155), Gd^(154), and Gd^(152) are 21.863, 24.835, 15.652, 20.466, 14.800, 2.1809, and 0.2029, respectively. Because of the higher precision, these abundances should replace the currently accepted values.

Meteoritic whitlockite containing excess fission tracks has a large concentration of excess neutron-rich xenon isotopes which is 25 times that calculated from the track density. The isotopic spectrum is identical to that calculated previously for the Pasamonte achondrite. These results uniquely associate this spectrum with in situ fission. Identification of the fissioning nucleus as Pu244 gives Pu244/U238 ≅ 1/30 at the time of xenon retention. Neither "sudden" nor "uniform" nucleosynthetic models give consistent solutions for Pu244/U238 and U235/U238.

Whitlockite from the St. Severin chondrite, previously shown to contain excess fission tracks, is here shown to have a large concentration of excess neutron-rich xenon isotopes. The concentration of excess heavy Xe in the whitlockite is about twenty-five times that calculated from the track density. An isotopic spectrum is deduced that is identical to the spectrum calculated previously for excess heavy xenon in the Pasamonte achondrite. These results uniquely associate this xenon spectrum with in situ fission in meteorites. Chemical arguments support the correlation of this with Pu^(244). Identification of the fissioning nucleus as Pu^(244) gives Pu^(244)/U^(238) ≈ 1/30. Neither ‘sudden’ nor ‘uniform’ nucleosynthetic models give consistent solutions for Pu^(244)/U^(238) and U^(235)/U^(238).