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The primary goal of the Genesis Mission is to collect solar wind ions and, from their analysis, establish key isotopic ratios that will help constrain models of solar nebula formation and evolution. The ratios of primary interest include 17O/16O and 18O/16O to ±0.1%, 15N/14N to ±1%, and the Li, Be, and B elemental and isotopic abundances. The required accuracies in N and O ratios cannot be achieved without concentrating the solar wind and implanting it into low-background target materials that are returned to Earth for analysis. The Genesis Concentrator is designed to concentrate the heavy ion flux from the solar wind by an average factor of at least 20 and implant it into a target of ultra-pure, well-characterized materials. High-transparency grids held at high voltages are used near the aperture to reject >90% of the protons, avoiding damage to the target. Another set of grids and applied voltages are used to accelerate and focus the remaining ions to implant into the target. The design uses an energy-independent parabolic ion mirror to focus ions onto a 6.2 cm diameter target of materials selected to contain levels of O and other elements of interest established and documented to be below 10% of the levels expected from the concentrated solar wind. To optimize the concentration of the ions, voltages are constantly adjusted based on real-time solar wind speed and temperature measurements from the Genesis ion monitor. Construction of the Concentrator required new developments in ion optics; materials; and instrument testing and handling.

A verification technique for use at reprocessing facilities, which integrates existing technologies to strengthen safeguards through the use of environmental monitoring, has been developed at Los Alamos National Laboratory. This technique involves the measurement of isotopic ratios of stable noble fission gases from on-stack emissions during reprocessing of spent fuel using high-precision mass spectrometry. These results are then compared to a database of calculated isotopic ratios using a data analysis method to determine specific fuel parameters (e.g., burnup, fuel type, reactor type, etc.). These inferred parameters can be used to verify operator declarations. The integrated system (mass spectrometry, reactor modeling, and data analysis) has been validated using on-stack measurements during reprocessing of fuel from a US production reactor. These measurements led to an inferred burnup that matched the declared burnup to within 3.9%, suggesting that the current system is sufficient for most safeguards applications. Partial system validation using gas samples from literature measurements of power reactor fuel has been reported elsewhere. This has shown that the technique developed here may have some difficulty distinguishing pressurized water reactor (PWR) from boiling water reactor (BWR) fuel; however, it consistently can distinguish light water reactor (either PWR or BWR) fuels from other reactor fuel types. Future validations will include advanced power reactor fuels (such as breeder reactor fuels) and research reactor fuels as samples become available.

21 Ne depth profiles measured from amalgamated samples of sand-sized quartz from the Quaternary Bandelier Tuff were used to estimate inheritance-corrected exposure ages in stream terraces and an alluvial fan on the Pajarito Plateau. Stable alluvium and associated soils display a downward decreasing (Type I) nuclide profile pattern. Bioturbated colluvium with uniform (Type III) nuclide concentrations has buried these alluvial surfaces. Another possible profile type with downward increasing nuclide concentrations (Type II) is described but was not found on the Pajarito Plateau. We present mathematical models for each of the profile patterns relating nuclide concentration to inheritance, time-averaged bulk density, and either exposure time or burial rate. Curve fits of Type I profiles are used to estimate the age of alluvial landforms. A burial correction technique for deposits buried by younger colluvium is also presented. Inheritance- and burial-corrected 21 Ne surface exposure ages of 144±17 ka and 63±8 ka for two Pajarito Plateau stream terraces agree within error with independent soil profile development index dates of 160 ka and 68–78 ka. A soil overlying the 50–60 ka El Cajete pumice yields an inheritance-corrected 21 Ne exposure age of 44±11 ka that also agrees closely with a 14 C age on soil charcoal of 41 ka. These results demonstrate that reliable cosmogenic 21 Ne exposure ages can be obtained for fine-grained alluvial surfaces with the depth profile technique.

Measurements of cosmogenic nuclides made in situ in the Earth's surface are being used to help resolve a wide range of geologic and chronologic questions. Cosmogenic nuclides (3He, 10Be, 14C, 21Ne, 26Al 36C1 are presently used) can reveal rock exposure history information leading to estimates of timing of surface forming events, rates and styles of erosion, and timing and durations of episodes of burial. Depending on the problems being tackled, a significant source of error (±10–25%) for any cosmogenic nuclide method is the present uncertainty in the spatial and temporal variability of the rates of production of these in-situ nuclides.

Dating of very young igneous activity has been hampered by lack of suitable chronometers. We report here the results of 3He surface exposure dating (Kurz, 1986a,b; Craig and Poreda, 1986) for lavas from the Potrillo volcanic field. This field is particularly suited to the technique because it has well-preserved, young (

The formation of stone pavements, a ubiquitous gravel armor mantling landforms in arid regions of the world, has been previously attributed to erosion by wind and water or alternating shrinking and swelling of soil horizons, implying that gravel is concentrated at the land surface in a time-transgressive manner. A newly proposed model for pavement evolution differs from these models in that pavement clasts are continuously maintained atthelandsurfaceinresponsetodepositionandpedogenicmodificationofwindblowndust. In-situ cosmogenic 3 He surface-exposure ages on volcanic and alluvial landforms in the Mojave Desert of California are used to understand pavement evolution over geologic time scales and to test this new model. These exposure ages are stratigraphically consistent, show internal consistency at each site, and, for stone pavements adjacent to pristine, continuously exposed volcanic bedrock, are indistinguishable at the 1! level. We conclude that stone pavements are born at the surface and that pavements may provide one of the longest-term records of geologic, hydrologic, and climatic processes operating on desert surfaces.

Concordant radiocarbon and cosmogenic [sup 3]He dates of 3 and 11 ka on basalt flows and associated scoria deposits from the Zuni-Bandera volcanic field in New Mexico further substantiate published production rates and latitudinal and altitudinal corrections for [sup 3]He. Identical [sup 3]He concentrations in coexisting olivine and clinopyroxene confirm that these two minerals have very similar production rates. A cosmogenic [sup 3]He date of 57 ka on another flow is concordant with a U-series date and is younger than two K-Ar dates, suggesting that this flow contains excess [sup 40]Ar. This excess [sup 40]Ar is also evident in gases released by vacuum crushing of olivine-clinopyroxene fractions from all three flows. 27 refs., 3 figs., 3 tabs.

The deuterated methanes, 13CD4 and 12CD4, are useful as tracers for long-range (>500 km) atmospheric transport. They are easily synthesized and released. Sampling is accomplished by collecting about 330 l of air and chromatographically separating the methane fraction, which is then analyzed by mass spectrometry for the 13 CD 4 12 CH 4 and 12 CD 4 12 CH 4 ratios. Detection limits in air are about 7 × 10−16 STP mol m−3 for 13CD4 and 2 × 10−15 STP mol m−3 for 12CD4.

Carbon stable isotopic composition of the major carbonaceous component in enstatite chondrites varies with petrologic type. Investigation of a suite of HF/HCl-resistant residues has shown that this variation is due to an inherent difference in δ 13 C of the carbon, and is not a result of the presence of small amounts of isotopically anomalous carbon-bearing components. These latter do occur in type EH3 and EH4 chondrites, in concentrations similar to those found in C1 and C2 carbonaceous chondrites. Combustion of the major carbon component (apparently elemental carbon, not necessarily graphite) occurs at relatively higher temperatures in enstatite chondrites of increasing petrologic type. This is considered to reflect an increase in crystallinity or ordering of the carbonaceous component, and is a measure of the degree of thermal processing to which the meteorites have been subjected during accretion and/or metamorphism.