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Electron probe microanalyzer measurements of trace elements with high accuracy are challenging. Accurate Al measurements in olivine are required to calibrate SIMS implant reference materials for measurement of Al in the solar wind. We adopt a combined EPMA/SIMS approach that is useful for producing SIMS reference materials as well as for EPMA at the ~100 μg g(−1) level. Even for mounts not polished with alumina photoelectron spectroscopy shows high levels of Al surface contamination. In order to minimize electron beam current density, a rastered 50 × 100 μm electron beam was adequate and minimized sensitivity to small Al-rich contaminants. Reproducible analyses of eleven SIMS-cleaned spots on San Carlos olivine agreed at 69.3 ± 1.0 μg g(−1)• The known Al mass fraction was used to calibrate an Al implant into San Carlos. Accurate measurements of Al were made for olivines in the pallasites: lmilac, Eagle Station and Springwater. Our focus was on Al in olivine, but our technique could be refined to give accurate electron probe measurements for other contamination-sensitive trace elements. For solar wind, it is projected that the Al/Mg abundance ratio can be determined to 6%, a factor of 2 more precise than the solar spectroscopic ratio.

The Genesis mission captured Solar Wind (SW) and delivered it to Earth for laboratory analyses. Due to advanced mass spectrometric techniques developed specifically for analyses of returned Genesis SW-collectors, SW-oxygen, nitrogen and noble gas isotopes have been successfully measured providing new insights for cosmo- and geochemistry. SW-Xe collected by Genesis is the heaviest and the least abundant SW element analyzed. Here we describe in detail the experimental improvements we made over last 5 years and a latest refined SW-Xe isotopic composition. Combined with earlier, already published SW-Xe analyses, our new results provide the best current estimate for SW-Xe collected by Genesis: 136Xe/130Xe = 1.818 ± 0.004; 134Xe/130Xe = 2.242 ± 0.005; 132Xe/130Xe = 6.063 ± 0.010; 131Xe/130Xe = 5.010 ± 0.012; 129Xe/130Xe = 6.314 ± 0.013; 128Xe/130Xe = 0.510 ± 0.001; 126Xe/130Xe = 0.0256 ± 0.0004; 124Xe/130Xe = 0.0292 ± 0.0004 (all errors are 1σ). The achieved precision allows resolving small, but now statistically significant isotopic difference between solar wind Xe and Xe trapped in lunar regolith samples. This emerging difference, not apparent prior to this study, likely points to the composition of indigenous lunar Xe and to the temporal evolution of terrestrial Xe. Combining our Xe fluence with that for other high first ionization potential (FIP) elements, we find that the depletion of elements with the FIP greater than 12 eV is not constant but monotonically decreases as FIP increases.

NASA's Genesis mission was flown to capture samples of the solar wind and return them to the Earth for measurement. The purpose of the mission was to determine the chemical and isotopic composition of the Sun with significantly better precision than known before. Abundance data are now available for noble gases, magnesium, sodium, calcium, potassium, aluminum, chromium, iron, and other elements. Here, we report abundance data for hydrogen in four solar wind regimes collected by the Genesis mission (bulk solar wind, interstream low-energy wind, coronal hole high-energy wind, and coronal mass ejections). The mission was not designed to collect hydrogen, and in order to measure it, we had to overcome a variety of technical problems, as described herein. The relative hydrogen fluences among the four regimes should be accurate to better than ±5-6%, and the absolute fluences should be accurate to ±10%. We use the data to investigate elemental fractionations due to the first ionization potential during acceleration of the solar wind. We also use our data, combined with regime data for neon and argon, to estimate the solar neon and argon abundances, elements that cannot be measured spectroscopically in the solar photosphere.

The distribution of solar-wind ions in Genesis mission collectors, as determined by depth profiling analysis, constrains the physics of ion-solid interactions involving the solar wind. Thus, they provide an experimental basis for revealing ancient solar activities represented by solar-wind implants in natural samples. We measured the first depth profile of ^4He in a Genesis collector; the shallow implantation (peaking at

We have measured the isotopic composition and fluence of solar-wind nitrogen in a diamond-like-carbon collector from the Genesis B/C array. The B and C collector arrays on the Genesis spacecraft passively collected bulk solar wind for the entire collection period, and there is no need to correct data for instrumental fractionation during collection, unlike data from the Genesis “Concentrator.” This work validates isotopic measurements from the concentrator by Marty et al. (2010, 2011); nitrogen in the solar wind is depleted in ^(15)N relative to nitrogen in the Earth’s atmosphere. Specifically, our array data yield values for ^(15)N/^(14)N of (2.17 ± 0.37) × 10^(−3) and (2.12 ± 0.34) × 10^(−3), depending on data-reduction technique. This result contradicts preliminary results reported for previous measurements on B/C array materials by Pepin et al. (2009), so the discrepancy between Marty et al. (2010, 2011) and Pepin et al. (2009) was not due to fractionation of solar wind by the concentrator. Our measured value of ^(15)N/^(14)N in the solar wind shows that the Sun, and by extension the solar nebula, lie at the low-^(15)N/^(14)N end of the range of nitrogen isotopic compositions observed in the solar system. A global process (or combination of processes) must have operated in interstellar space and/or during the earliest stages of solar system formation to increase the ^(15)N/^(14)N ratio of the solar system solids. We also report a preliminary Genesis solar-wind nitrogen fluence of (2.57 ± 0.42) × 10^(12) cm^(−2). This value is higher than that derived by backside profiling of a Genesis silicon collector (Heber et al. 2011a).

We present bulk solar wind isotopic and elemental ratios for Ar, Kr, and Xe averaged from up to 14 individual analyses on silicon targets exposed to the solar wind for ~2.3 years during NASA’s Genesis mission. All averages are given with 1σ standard errors of the means and include the uncertainties of our absolute calibrations. The isotopic ratios ^(86)Kr/^(84)Kr and ^(129)Xe/^(132)Xe are 0.303 ± 0.001 and 1.06 ± 0.01, respectively. The elemental ratios ^(36)Ar/^(84)Kr and ^(84)Kr/^(132)Xe are 2390 ± 120 and 9.9 ± 0.3, respectively. Average fluxes of ^(84)Kr and ^(132)Xe in the bulk solar wind in atoms/(cm^2 s) are 0.166 ± 0.009 and 0.017 ± 0.001, respectively. The flux uncertainties also include a 2% uncertainty for the determination of the extracted areas. The bulk solar wind ^(36)Ar/^(38)Ar ratio of 5.50 ± 0.01 and the ^(36)Ar flux of 397 ± 11 atoms/(cm^2s) determined from silicon targets agree well with the ^(36)Ar/^(38)Ar ratio and the ^(36)Ar flux determined earlier on a different type of target by Heber et al. (2009). A comparison of the solar wind noble gas/oxygen abundance ratios with those in the solar photosphere revealed a slight enrichment of Xe and, within uncertainties a roughly uniform depletion of Kr–He in the solar wind, possibly related to the first ionization potentials of the studied elements. Thus, the solar wind elemental abundances He–Kr display within uncertainties roughly photospheric compositions relative to each other. A comparison of the Genesis data with solar wind heavy noble gas data deduced from lunar regolith samples irradiated with solar wind at different times in the past reveals uniform ^(36)Ar/^(84)Kr ratios over the last 1–2 Ga but an increase of the ^(84)Kr/^(132)Xe ratio of about a factor of 2 during the same time span. The reason for this change in the solar wind composition remains unknown.

We report concentrations and isotopic compositions of He, Ne, and Ar measured with high spatial resolution along a radial traverse of a silicon carbide (SiC) quadrant of the Genesis mission concentrator target. The Ne isotopic composition maps instrumental fractionation as a function of radial position in the target: the maximum observed isotopic fractionation is approximately 33‰ per mass unit between the center and periphery. The Ne fluence is enhanced by a factor of 43 at the target center and decreases to 5.5 times at the periphery relative to the bulk solar wind fluence. Neon isotopic profiles measured along all four arms of the "gold cross" mount which held the quadrants in the concentrator target demonstrate that the concentrator target was symmetrically irradiated during operation as designed. We used implantation experiments of Ne into SiC and gold to quantify backscatter loss and isotopic fractionation and compared measurements with numerical simulations from the code "stopping and range of ions in matter." The ^(20)Ne fluence curve as a function of radial distance on the target may be used to construct concentration factors relative to bulk solar wind for accurate corrections for solar wind fluences of other light elements to be measured in the concentrator target. The Ne isotopic composition as a function of the radial distance in the SiC quadrant provides a correction for the instrumental mass-dependent isotopic fractionation by the concentrator and can be used to correct measured solar wind oxygen and nitrogen isotopic compositions to obtain bulk solar wind isotopic compositions.

We present the first experimental radium mineral/melt partitioning data, specifically between anorthite and a CMAS melt at atmospheric pressure. ^(226)Ra disequilibria are an important chronometer of recent magmatic activity. Ion microprobe measurement of coexisting anorthite and glass phases produces a molar D_Ra = 0.040 ± 0.006 and D_(Ra)/D_(Ba) = 0.24 ± 0.05 at 1400 °C. Our results indicate that lattice strain partitioning models fit the divalent (Ca, Sr, Ba, Ra) partition coefficient data of this study well, supporting previous work on crustal melting and magma chamber dynamics that has relied on such models to approximate radium partitioning behavior in the absence of experimentally determined values.

Ion microprobe elemental and isotopic determinations can be precise but difficult to quantify. Error is introduced when the reference material and the sample to be analysed have different compositions. Mitigation of such “matrix effects” is possible using ion implants. If a compositionally homogeneous reference material is available which is “matrix-appropriate,” i.e., close in major element composition to the sample to be analysed, but having an unknown concentration of the element, E, to be determined, ion implantation can be used to introduce a known amount of an E isotope, calibrating the E concentration and producing a matrix-appropriate calibrator. Nominal implant fluences (ions cm^(−2)) are inaccurate by amounts up to approximately 30%. However, ion implantation gives uniform fluences over large areas, thus it is possible to “co-implant” an additional reference material of any bulk composition having known amounts of E, independently calibrating the implant fluence. Isotope-ratio measurement standards can be produced by implanting two different isotopes, but permil level precision requires post-implant calibration of the implant isotopic ratio. Examples discussed include: (1) standardising Li in melilite; (2) calibrating a ^(25)Mg implant fluence using NIST SRM 617 glass; and (3) using Si co-implanted with ^(25)Mg alongside NIST SRM 617 to produce a calibrated measurement of Mg in Si.

We propose a theory for crystal-melt trace element partitioning that considers the energetic consequences of crystal-lattice strain, of multi-component major-element silicate liquid mixing, and of trace-element activity coefficients in melts. We demonstrate application of the theory using newly determined partition coefficients for Ca, Mg, Sr, and Ba between pure anorthite and seven CMAS liquid compositions at 1330 °C and 1 atm. By selecting a range of melt compositions in equilibrium with a common crystal composition at equal liquidus temperature and pressure, we have isolated the contribution of melt composition to divalent trace element partitioning in this simple system. The partitioning data are fit to Onuma curves with parameterizations that can be thermodynamically rationalized in terms of the melt major element activity product (a_(Al_2O_3))(a_(SiO_2_)^2 and lattice strain theory modeling. Residuals between observed partition coefficients and the lattice strain plus major oxide melt activity model are then attributed to non-ideality of trace constituents in the liquids. The activity coefficients of the trace species in the melt are found to vary systematically with composition. Accounting for the major and trace element thermodynamics in the melt allows a good fit in which the parameters of the crystal-lattice strain model are independent of melt composition.

A new generation of time-of-flight mass spectrometers that implement ion sputtering and laser desorption for probing solid samples and can operate in regimes of laser post-ionization secondary neutral mass spectrometry and secondary ion mass spectrometry is being developed at Argonne National Laboratory. These new instruments feature novel ion optical systems for efficient extraction of ions from large laser post-ionization volumes and for lossless transport of these ions to detectors. Another feature of this design is a new in-vacuum all-reflecting optical microscope with 0.5-μm resolution. Advanced ion and light optics and three ion sources, including a liquid metal ion gun (focusable to 50 nm) and a low energy ion gun, give rise to an instrument capable of quantitative analyses of samples for the most challenging applications, such as determining elemental concentrations in shallow implants at ultra-trace levels (for example, solar wind samples delivered by NASA Genesis mission) and analyzing individual sub-micrometer particles on a sample stage (such as, interstellar dust delivered by NASA Stardust mission). Construction of a prototype instrument has been completed and testing is underway. A more advanced instrument of similar design is under construction. The overall design of the new instrument and the innovations that make it unique are outlined. Results of the first tests to characterize its analytical capabilities are presented also.

Apatite, titanite and olivine samples were bombarded with a ~ 150 MeV proton beam to produce ~ 10^8 atoms/mg of spallation ^3He. High-precision stepped-heating experiments were then performed in which the artificial ^3He and, for apatite and titanite, the natural radiogenic ^4He were measured to characterize the diffusive behavior of each isotope. Helium-3 diffusion coefficients are in excellent agreement with concurrently and/or previously determined He diffusion coefficients for each mineral. Our results indicate that proton-induced ^3He is uniformly distributed and that radiation damage associated with a proton fluence of ~ 5 x 10^(14) protons/cm^2 does not cause noticeable changes in ^4He diffusion behavior in at least apatite and titanite. Proton-induced ^3He can therefore be used to establish He diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural ^4He distribution is inhomogeneous. In addition,step-heating ^4He/^3He analysis of a mineral with a uniform synthetic ^3He concentration provides a means by which a natural ^4He distribution can be determined.

The design and operation of the Genesis Solar-Wind Concentrator relies heavily on computer simulations. The computer model is described here, as well as the solar wind conditions used as simulation inputs, including oxygen charge state, velocity, thermal, and angular distributions. The simulation included effects such as ion backscattering losses, which also affect the mass fractionation of the instrument. Calculations were performed for oxygen, the principal element of interest, as well as for H and He. Ion fluences and oxygen mass fractionation are determined as a function of radius on the target. The results were used to verify that the instrument was indeed meeting its requirements, and will help prepare for distribution of the target samples upon return of the instrument to earth. The actual instrumental fractionation will be determined at that time by comparing solar-wind neon isotope ratios measured in passive collectors with neon in the Concentrator target, and by using a model similar to the one described here to extrapolate the instrumental fractionation to oxygen isotopes.

International audience; A method to quantitatively determine the fluences of shallowly-implanted solar wind ions returned to Earth by the Genesis Discovery mission is described. Through backside depth-profiling, we recover nearly complete depth profiles of implanted solar wind for several nonvolatile elements, including Mg, Al, Ca, Cr, and, to a lesser extent, Na, in silicon targets that collected bulk solar wind and solar wind from specific velocity regimes. We also determine the fluences of the volatile elements C, N, and O in silicon targets that collected bulk solar wind. By the use of appropriately calibrated ion implanted standards, fluences as low as 2 x 10(10) atoms cm(-2) can be determined with precision and accuracy typically in the few percent range. Specific approaches to sample preparation, sputtering artifacts during depth profiling by secondary ion mass spectrometry, and quantification including the production of ion implant standards are discussed. (C) 2014 Elsevier B.V. All rights reserved.

RIMS depth profiles have been measured for Cr and Ca in Genesis solar wind collector made from Si and compared to such measurements for ion-implanted Si reference material. The presence of surface contamination has been shown to be a significant factor influencing the total Ca and Cr fluence measured in the Genesis collectors. A procedure to remove the contaminant signal from these depth profiles using the reference material implanted with a minor isotope demonstrated that 36% of the measured Ca fluence in our Genesis sample comes from terrestrial contamination.

The thermal diffusion of an Mg implant in Si has been measured with SIMS and compared to RIMS (resonant ionisation mass spectrometry) measurements of Mg implantation and diffusion in Si wafers exposed to solar wind irradiation in the NASA Genesis mission. The Genesis samples show much more surface segregation that the samples annealed in the laboratory, due to diffusion and segregation of the implanted Mg to the heavily damaged near surface regions of the Genesis wafers. This Mg transport has been modeled by solving a set of stiff differential equations and found to agree with RIMS measurements for a Mg interstitial migration energy of 0.7 eV.

To evaluate the isotopic composition of the solar nebula from which the planets formed, the relation between isotopes measured in the solar wind and on the Sun's surface needs to be known. The Genesis Discovery mission returned independent samples of three types of solar wind produced by different solar processes that provide a check on possible isotopic variations, or fractionation, between the solar-wind and solar-surface material. At a high level of precision, we observed no significant inter-regime differences in 20 Ne/ 22 Ne or 36 Ar/ 38 Ar values. For 20 Ne/ 22 Ne, the difference between low- and high-speed wind components is 0.24 ± 0.37%; for 36 Ar/ 38 Ar, it is 0.11 ± 0.26%. Our measured 36 Ar/ 38 Ar ratio in the solar wind of 5.501 ± 0.005 is 3.42 ± 0.09% higher than that of the terrestrial atmosphere, which may reflect atmospheric losses early in Earth's history.

One of the major goals of the Genesis Mission was to refine our knowledge of the isotopic composition of the heavy noble gases in solar wind and, by inference, the Sun, which represents the initial composition of the solar system. This has now been achieved with permil precision: ^(36)Ar/^(38)Ar = 5.5005 ± 0.0040, ^(86)Kr/^(84)Kr = .3012 ± .0004, ^(83)Kr/^(84)Kr = .2034 ± .0002, ^(82)Kr/^(84)Kr = .2054 ± .0002, ^(80)Kr/^(84)Kr = .0412 ± .0002, ^(78)Kr/^(84)Kr = .00642 ± .00005, ^(136)Xe/^(132)Xe = .3001 ± .0006, ^(134)Xe/^(132)Xe = .3691 ± .0007, ^(131)Xe/^(132)Xe = .8256 ± .0012, ^(130)Xe/^(132)Xe = .1650 ± .0004, ^(129)Xe/^(132)Xe = 1.0405 ± .0010, ^(128)Xe/^(132)Xe = .0842 ± .0003, ^(126)Xe/^(132)Xe = .00416 ± .00009, and ^(124)Xe/^(132)Xe = .00491 ± .00007 (error-weighted averages of all published data). The Kr and Xe ratios measured in the Genesis solar wind collectors generally agree with the less precise values obtained from lunar soils and breccias, which have accumulated solar wind over hundreds of millions of years, suggesting little if any temporal variability of the isotopic composition of solar wind krypton and xenon. The higher precision for the initial composition of the heavy noble gases in the solar system allows (1) to confirm that, exept ^(136)Xe and ^(134)Xe, the mathematically derived U–Xe is equivalent to Solar Wind Xe and (2) to provide an opportunity for better understanding the relationship between the starting composition and Xe-Q (and Q-Kr), the dominant current “planetary” component, and its host, the mysterious phase-Q.

The Genesis mission Solar Wind Concentrator was built to enhance fluences of solar wind by an average of 20x over the 2.3 years that the mission exposed substrates to the solar wind. The Concentrator targets survived the hard landing upon return to Earth and were used to determine the isotopic composition of solar-wind—and hence solar—oxygen and nitrogen. Here we report on the flight operation of the instrument and on simulations of its performance. Concentration and fractionation patterns obtained from simulations are given for He, Li, N, O, Ne, Mg, Si, S, and Ar in SiC targets, and are compared with measured concentrations and isotope ratios for the noble gases. Carbon is also modeled for a Si target. Predicted differences in instrumental fractionation between elements are discussed. Additionally, as the Concentrator was designed only for ions ≤22 AMU, implications of analyzing elements as heavy as argon are discussed. Post-flight simulations of instrumental fractionation as a function of radial position on the targets incorporate solar-wind velocity and angular distributions measured in flight, and predict fractionation patterns for various elements and isotopes of interest. A tighter angular distribution, mostly due to better spacecraft spin stability than assumed in pre-flight modeling, results in a steeper isotopic fractionation gradient between the center and the perimeter of the targets. Using the distribution of solar-wind velocities encountered during flight, which are higher than those used in pre-flight modeling, results in elemental abundance patterns slightly less peaked at the center. Mean fractionations trend with atomic mass, with differences relative to the measured isotopes of neon of +4.1±0.9 ‰/amu for Li, between -0.4 and +2.8 ‰/amu for C, +1.9±0.7‰/amu for N, +1.3±0.4 ‰/amu for O, -7.5±0.4 ‰/amu for Mg, -8.9±0.6 ‰/amu for Si, and -22.0±0.7 ‰/amu for S (uncertainties reflect Monte Carlo statistics). The slopes of the fractionation trends depend to first order only on the relative differential mass ratio, Δ m/ m. This article and a companion paper (Reisenfeld et al. 2012, this issue) provide post-flight information necessary for the analysis of the Genesis solar wind samples, and thus serve to complement the Space Science Review volume, The Genesis Mission (v. 105, 2003).

Experiments were conducted in air and at low oxygen fugacity (f_O_2)) to evaluate Mg and Ti partitioning between anorthite and liquid (D_(Mg) and D_(Ti) in a synthetic composition similar to that of a Type B Ca, AI-rich inclusion (CAI). The starting material showed a range of compositions, which allowed assessment of the composition dependence of D_(Mg) and D_(Ti) in this system. Additional experiments using a homogeneous split of the same material investigated the effect of oxygen fugacity on the partitioning of Ti^(3+) and Ti^(4+) between anorthite and liquid. The low foe charges were purple, consistent with the presence of significant amounts of Ti^(3+).This was verified by electron spin resonance (ESR) spectra, and quantitative estimates of Ti^(3+) contents were obtained using ESR. The Ti and Mg partition coefficients in the air run using the homogeneous starting material are similar (0.034 and 0.036, respectively) and consistent with those determined in other studies. However, D_(Ti) at low f_(O_2) is slightly greater than D_(Ti) in the air experiments. Using Ti^(3+)/total Ti from the ESR measurements, D_(Ti^(3+)) is calculated to be about 0.040. The range of compositions reveal a clustering of D_(Mg) and D_(Ti) within charges, but a wide range of D_s between charges of different composition. A well-defined inverse correlation exists between D_(Mg) and D_(Ti). This variation is not due to temperature-dependence, but is instead due to the dependence of D_(Mg) and D_(Ti) on liquid composition (Si and Al in particular). D_(Mg) correlates positively with Si content and negatively with Al content, while D_(Ti) shows the opposite correlations. The results of these experiments have interesting implications for the petrogenesis of Type B CAIs and for substitution mechanisms of Mg, Ti^(4+), and Ti^(3+) into anorthite. Crystallization models for Type B CAIs permit certain predictions concerning trace element systematics in plagioclase. The Mg and Ti systematics are best explained by a fractional crystallization model where plagioclase crystallizes very late (>95% crystallization), and D_(Ti^(3+)). is equal to D_(Ti^(4+)). The results from our experiments support this model for the relative partitioning of Ti^(4+) and Ti^(3+) between plagioclase and liquid. In addition, the dependence of D_(Mg), and D_(Ti) on the Si content of a Type B CAI liquid helps explain systematics expected during late-stage crystallization of plagioclase. The composition dependence of D_(Mg) and D_(Ti) also allows assessment of substitution mechanisms in anorthite using a crystallization reaction approach. Using these methods, a plausible mechanism for Mg involves substitution for tetrahedral A1 by the reaction Mg^(2+) + Si^(4+) = 2AI^(3+), consistent with that proposed by previous workers. The systematics are also consistent with Ti^(4+) and Ti^(3+) substitution for tetrahedral Si^(4+) by the reactions 2Al^(3+) + Ti^(4+) = Ca^(2+) + 2Si^(4+) and Al^(3+) + Ti^(3+) = Ca^(2+) + Si^(4+), respectively.

Total reflection X-ray fluorescence spectrometry (TXRF) was used to analyze residual surface contamination on Genesis solar wind samples and to evaluate different cleaning methods. To gauge the suitability of a cleaning method, two samples were analyzed following cleaning by lab-based TXRF. The analysis comprised an overview and a crude manual mapping of the samples by orienting them with respect to the incident X-ray beam in such a way that different regions were covered. The results show that cleaning with concentrated hydrochloric acid and a combination of hydrochloric acid and hydrofluoric acid decreased persistent inorganic contaminants substantially on one sample. The application of CO2 snow for surface cleaning tested on the other sample appears to be effective in removing one persistent Genesis contaminant, namely germanium. Unfortunately, the TXRF analysis results of the second sample were impacted by relatively high background contamination. This was mostly due to the relatively small sample size and that the solar wind collector was already mounted with silver glue for resonance ion mass spectrometry (RIMS) on an aluminium stub. Further studies are planned to eliminate this problem. In an effort to identify the location of very persistent contaminants, selected samples were also subjected to environmental scanning electron microscopy. The results showed excellent agreement with TXRF analysis.

We present the elemental and isotopic composition of noble gases in the bulk solar wind collected by the NASA Genesis sample return mission. He, Ne, and Ar were analyzed in diamond-like carbon on a silicon substrate (DOS) and ^(84),^(86)Kr and ^(129),^(132)Xe in silicon targets by UV laser ablation noble gas mass spectrometry. Solar wind noble gases are quantitatively retained in DOS and with exception of He also in Si as shown by a stepwise heating experiment on a flown DOS target and analyses on other bulk solar wind collector materials. Solar wind data presented here are absolutely calibrated and the error of the standard gas composition is included in stated uncertainties. The isotopic composition of the light noble gases in the bulk solar wind is as follows: ^3He/^4He: (4.64 ± 0.09) × 10^(−4), ^(20)Ne/^(22)Ne: 13.78 ± 0.03, ^(21)Ne/^(22)Ne: 0.0329 ± 0.0001, ^(36)Ar/^(38)Ar 5.47 ± 0.01. The elemental composition is:^4He/^(20)Ne: 656 ± 5, and ^(20)Ne/^(36)Ar 42.1 ± 0.3. Genesis provided the first Kr and Xe data on the contemporary bulk solar wind. The preliminary isotope and elemental composition is: ^(86)Kr/^(84)Kr: 0.302 ± 0.003, ^(129)Xe/^(132)Xe: 1.05 ± 0.02, ^(36)Ar/^(84)Kr 2390 ± 150, and ^(84)Kr/^(132)Xe 9.5 ± 1.0. The ^3He/^4He and the ^4He/^(20)Ne ratios in the Genesis DOS target are the highest solar wind values measured in exposed natural and artificial targets. The isotopic composition of the other noble gases and the Kr/Xe ratio obtained in this work agree with data from lunar samples containing “young” (~100 Ma) solar wind, indicating that solar wind composition has not changed within at least the last 100 Ma. Genesis could provide in many cases more precise data on solar wind composition than any previous experiment. Because of the controlled exposure conditions, Genesis data are also less prone to unrecognized systematic errors than, e.g., lunar sample analyses. The solar wind is the most authentic sample of the solar composition of noble gases, however, the derivation of solar noble gas abundances and isotopic composition using solar wind data requires a better understanding of fractionation processes acting upon solar wind formation.

One of the primary objectives of the Genesis sample return mission is to measure the oxygen isotopic composition of the Sun to permil-level precision. The returned samples pose a unique analytical challenge, and around the world, there has been parallel development of several competing techniques to make the oxygen measurement on the Genesis concentrator samples. At UCLA, we have developed a hybrid instrument: a secondary ion mass spectrometer (SIMS) front-end combined with an accelerator mass spectrometer (AMS), whose purpose is to eliminate molecular interferences via dissociation. We describe here the current status of the development of the instrument and the remaining issues to address before we request the Genesis samples for analysis.

Space Science Reviews, 130 (1-4), ISSN:1572-9672, ISSN:0038-6308

NASA's Genesis capsule, carrying the first samples ever returned from beyond the Moon, took a hard landing in the western Utah desert on 8 September after its parachutes failed to deploy Despite the impact, estimated at 310 km per hour, some valuable solar wind collector materials have been recovered. With these samples, the Genesis team members are hopeful that nearly all of the primary science goals may be met. The Genesis spacecraft was launched in August 2001 to collect and return samples of solar wind for precise isotopic and elemental analysis. The spacecraft orbited the Earth-Sun Lagrangian point (LI), ˜1.5 million km sunward of Earth, for 2.3 years. It exposed ultrapure materials—including wafers of silicon, silicon carbide, germanium, chemically deposited diamond, gold, aluminum, and metallic glass— to solar wind ions, which become embedded within the substrates' top 100 nm of these materials.

The partitioning of Pu and Sm between diopside/liquid and whitlockite/liquid has been investigated experimentally to evaluate the geochemical coherence of Pu and the light REEs. ^(Pu)D/^(Sm)D is 2 ~ for both diopsidic pyroxene and whitlockite. This small amount of fractionation would be decreased further if Pu were compared to Ce or Nd. Our experimental results thus validate the suggestion that Pu behaves as a LREE during igneous processes in reducing environments. Our data and the data of Ray et al. (1983) indicate that temperature rather than melt composition is the most important control on elemental partitioning. This is true even though we demonstrate that additions of only 1–2 wt.% of P2_O_5 to the diopside-anorthite-albite system change ^(Pu)D_(cpx) by a factor of two. Our data suggest that P_2O_5 in aluminosilicate melts serves as a complexing agent for the actinides and lanthanides.

Elemental abundances from Cl carbonaceous chondrite meteorites are thought to represent the average solar system (“cosmic”) composition, based on the agreement between Cl and solar photospheric abundances and on the smoothness of heavy element abundances of odd mass nuclei when plotted as a function of mass number. To test Cl elemental smoothness, we have analyzed Cl meteorites, using conventional PIXE (proton probe) techniques, where we have good sensitivity for the range of elements: Ni to Mo. Preliminary analyses indicate that elemental smoothness is only approximate, with possible deviations of 30% to perhaps even 50%. This may be due to chemical fractionation. Alternatively, explanations for nonsmooth behavior may be understandable with the aid of general ideas of n-capture nucleosynthesis. As Cl abundances are refined, it could be that the lack of elemental smoothness may provide the strongest argument for the identification of Cl with primordial solar system abundances.

A new method involving the detection of fission fragments in mica has been applied to the measurement of the fission cross section of the compound nucleus Tl201 produced by bombardments of Au197 with helium ions. These data have been interpreted in terms of an expression for the ratio of fission to neutron-emission probabilities similar to those used conventionally, but modified to include the effect of quantum-mechanical barrier penetrability. In this way a height of 22.5±1.5 MeV was found for the fission barrier of Tl201 and a lower limit on the width could be established. The above value of the barrier, when interpreted on the basis of the liquid-drop theory, leads to an accurate determination of the ratio of the electrostatic to the surface energy of nuclei. This serves to establish the constant of proportionality between the "fissionability parameter" x and the value of Z2/A as follows: x=(Z2/A)/(48.4±0.5). This measured barrier height, when added to the ground-state mass of Tl201, gives a saddle-point mass of this nucleus equal to 200.9949±0.0015 mass units (carbon scale).

Rb Sr isotopic analyses were made on silicate inclusions from Kodaikanal, a brecciated fine octahedrite. Twelve analyses of different mineral fractions and separate inclusions were made. The silicates in this iron meteorite are highly enriched in alkalis and show ^(87)Sr/^(86)Sr ratios ranging up to 8.8. The samples lie on a well defined isochron on the Sr-Rb evolution diagram and indicate an age of 3.8 ± 0.1 × 10^9 y and an initial ^(87)Sr/^(86)Sr ratio between 0.69 and 0.73. These data provide unambiguous evidence for the ‘formation’ of younger solid objects in the solar system in a process which demands extensive chemical differentiation. This is evidence for an intermediate history for some meteoritic objects of a different sort than has been previously observed.

Chemical and mineralogical study of Kodaikanal meteorite silicate and metal phases, using optical, X ray and electron microprobe techniques

Rb-Sr measurements were made on silicate inclusions extracted from the iron meteorites Toluca, Odessa, Four Corners, Linwood, Pine River, Colomera and Weekeroo Station. Strontium isotopic analyses were made on samples as small as 24 ng. The typical Sr and Rb blanks were 2 × 10^(−9) g and 2 × 10^(−10) g, respectively. In certain cases it was possible to obtain relatively precise isochrons. With the exception of Colomera, all of these samples gave ages compatible with 4.4 to 4.8 × 10^9 y. The Colomera data scatter widely and do not meet the requirements for defining a reliable age. None of the samples are compatible with an age of 6 × 10^9 y. The primary strontium observed or estimated for Toluca and Pine River agrees with that obtained from achondrites. It is evident that extensive Rb-Sr isotopic studies may be made on a large number of rather typical iron meteorites.

Analyses of the argon and potassium in silicate inclusions were made on Weekerro Station, Toluca, Four Corners and Kodaikanal. The 40Ar40K ratios of all samples except Kodaikanal are compatible with an age of 4.5±0.15 × 109yr. These results are in agreement with the SrRb results obtained previously but not with the so-called 40Ar40K ages determined on iron meteorites by other workers. The 40Ar40K age of 3.5±0.1 × 109yr on Kodaikanal is consistent with the 87Sr87Rb age of 3.8±0.1 × 109yr. Estimates of the U + Th content of the silicate inclusions were made based on the 4He contents. Kodaikanal was found to have a very young exposure age for an iron meteorite (⪅40 m.y) based on upper limits to the cosmogenic He, Ne and Ar in the metal phase.

Measurements of the energy and mass distributions of fission fragments produced by the bombardment of a number of relatively light elements with heavy ions and alpha particles are presented. The results have been interpreted in terms of an approximate version of the liquid drop model which applies to this region of elements. The energies of both fission fragments from every event considered have been measured with solid state detectors, recorded in a correlated manner, and transformed to give mass-total kinetic energy density-of-events distributions. In some cases, data at several bombarding energies have been obtained. Comparisons with liquid drop calculations were made and good agreement was found in the gross features of the distributions, and in the nuclear temperature dependence of the widths.

Fission fragment kinetic energy measurements using semiconductor detectors were made for the alpha-induced fission of Au/sup 197/, Bi/sup 209/, Th/ sup 232/, and U/sup 238/ at alpha energi es of 21 to 65 Mev. The data were recorded as the number of events at fragment energies E/sub 1/ and E/sub 2/, N(E/ sub 1/,E/sub 2/). The data were then transformed into mass--total kinetic energy maps and analyzed by means of moments. The Bi and Au data are in good agreement with quantitative theoretical predictions from the liquid drop model available for the lighter elements. The U and Th data are discussed in terms of qualitative ideas that have been proposed to explain the properties of the fission process for the heavier elements. The changes in the U and Th mass and total kinetic energy distributions with excitation energy are emphasized. Pulse- height energy relations for the detectors used were obtained by a detailed comparison of detector and time-offlight results for the spontaneous fission of Cf/sup 252/. 54 references. (auth)