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A double focusing sector field mass filter used in Nier-Johnson geometry has been built in order to perform Kr isotope enrichment for 81 Kr and 85 Kr isotopes. The principle consists in implanting Kr+ ions accelerated at 7 keV in Al foils after separation using the magnetic sector. A specific ion source has been designed capable of generating high Kr+ ion beams (>0.5 μA) to transfer into the collecting Al foils in 3 to 5 h significant fractions of large Kr samples (1015 to 1016 atoms) initially introduced in the instrument. Implanted Kr isotopes can be further selectively released from the Al foil by surface ablation using an infrared laser beam. Implantation yields and enrichment factors are measured using a conventional mass spectrometer. Copyright © 2016 John Wiley & Sons, Ltd.

International audience; The northern Aquitaine basin (southwest France) is a large multi-layer aquifer system that contains groundwater with strong residence-time variability ranging from years to tens of thousands of years. This system constitutes an archive of paleoclimate variations. A multi-parameter approach involving isotopic tracers (14C, 18O, 2H) was used to determine the residence time of groundwater and to document climate fluctuations, while dissolved noble gases were used to estimate mean annual temperatures (noble gas recharge temperatures, NGRT) at the water table. Near-surface ground temperature reconstruction from 40 ka cal BP to the present was made using data collected from five aquifers. The coldest temperatures are recorded for late Marine Isotopic Stage (MIS) 3 and MIS 2, i.e. between 36 and 18 ka cal BP. The mean NGRT for the period 27–18 ka cal BP is estimated at 5.9 ± 0.9 °C, and a strong increase towards modern values (11–13 °C) is observed after 15 ka cal BP. The temperature change between the Holocene and the Last Glacial ranges from 5 to 7 °C, in agreement with previous NGRT studies in Europe. Since mean near-surface ground temperatures during the glacial were well above 0 °C, long-term presence of permafrost in northern Aquitaine is unlikely. However, a possible warm bias in reconstructed temperatures during the coldest events lies in the fact that NGRTs in cold regions do not reflect annual means but rather the ground temperature during the thaw months.

A new RIS-TOF instrument, called FAKIR (Facility for Analyzing Krypton Isotope Ratios), has been developed at CENBG in order to measure Kr isotope ratios with an extremely high sensitivity. The instrument uses a single color Kr ionization scheme with tunable coherent UV photons near 216.6 nm. A two-photon resonance excitation allows it to reach the 5p[5/2]2 excitation level followed by a single-photon ionization. Krypton ions are accelerated towards an electron multiplier. The instrument includes a cryogenic concentrator that increases the efficiency of the ion source and a new selecting system allowing the deflection of the abundant isotopes before they impact the detector. This device eliminates the blinding effect on the detector that alters the detection of the less abundant Kr isotopes. The current sensitivity of the instrument of ∼6700 atoms has been demonstrated by extracting the gas from 37 mg of the Boguslavka iron meteorite. The associated errors on the 81Kr isotope ratio measurements did not exceed ∼12%. A good agreement is observed with conventional mass spectrometry analysis, which requires several grams of material, by measuring the cosmic ray exposure age of the Boguslavka meteorite.

International audience; Before the excavation of the new gallery Ga08 in the Mont Terri Underground Rock Laboratory (Switzerland), which joined the existing gallery Ga04 in 2008, the end-face of gallery Ga04 was instrumented in 2007 to characterize the evolution of the rock mass with geochemical and geophysical methods. The noble gas content of a 12-m long horizontal borehole evidenced that desaturation processes occurred in the first 2 m, where pre-existing fractures accommodated the stress change during excavation of gallery Ga04 four years before. These first 2 m are associated with the so-called Excavation Damaged Zone (EDZ). As an inflow of pore water was observed in this borehole few weeks after its drilling, continuous self-potential (SP) measurements were performed to characterize its dynamics. After the drilling of new sub-horizontal boreholes in the end-face, strong localized variations of SP occurred. The comparison with the geological features of the rock mass suggests that these dynamic anomalies have to be associated with fluid circulation in pre-existing tectonic fractures that were primarily reactivated by the excavation of the gallery Ga04 and subsequently by the drilling operations.

Helium concentration measurements made on water and rock samples collected at various depths along a 2000 m depth borehole drilled in the eastern part of the Paris basin and reaching the Triassic conglomerates were used to establish a vertical profile of dissolved helium concentration throughout the entire Mesozoic sedimentary pile. Wireline logging tools were used to measure rock density, porosity and U and Th contents every 15 cm in the various formations. Samples from the deepest Muschelkalk and Buntsandstein show a very good agreement between measured and calculated 4He porewater contents. Shallower levels show lower and lower 4He concentrations compared to calculated values when going upwards. The data set obtained by wireline logging measurements was used as inputs for numerical simulations of 1D He production/diffusion throughout the 2000 m profile. Several assumptions regarding the transport properties in the various sedimentary layers were tested and all were found to yield fairly good agreement between modeled and measured He concentrations. There is no need to invoke either a transient regime or a deep crustal He flux in this “quiet” (seismically inactive) part of the Paris basin. Moreover, the modeling results suggest that the Keuper massive halite level associated with the upper Muschelkalk pre-evaporitic series efficiently isolates the overlying layers from any input from deeper formations in the Meuse/Haute Marne area.

International audience; A vertical distribution of helium-4 was obtained in pore-water from the Toarcian/Domerian argillaceous formation at Tournemire (South Aveyron, France). Most of the studied core samples were collected from two vertical air-drilled boreholes across the impervious argillaceous formation and penetrating the bounding aquifers. Accessible porosities for helium were assumed similar to those of water and calculated by weighting before and after heating the core samples. Helium-4 concentrations were obtained after out-gassing the rock samples in tight containers. The comparison of the total amount of 4He produced since the deposition of the formation with that presently measured in the rock reveals that more than 97% of 4He has been lost from the solid phase to pore-water and afterwards to the surrounding aquifers. Helium distribution in pore water shows a complex profile because of the presence of unexpectedly 4He-rich samples in the lower part of the Upper Toarcian level. In order to understand this distribution and to assess the transport of helium at the formation scale, a series of preliminary model calculations were performed using helium diffusion coefficients three times higher than those of water isotopes. The comparison between simulated and experimental data indicates that: (1) the helium profile could be similar to those of deuterium and chloride in pore-water if some unexpectedly 4He-rich samples are not considered; (2) the estimated transport parameters (at small scale) may be transposable at the formation scale with some uncertainties; (3) a steady state has most probably been reached between the in situ helium production and its loss towards the aquifers; (4) only 17-30Ma of diffusion time would be necessary to obtain steady state; this is short compared to the formation age (180Ma) and thus the helium profile cannot give very precise information about diffusion time in the massif, but is in agreement with the hypothesis that transport processes are dominated by diffusion. © 2011 Elsevier Ltd.

Galactic cosmic rays (GCR) provide information on the solar neighborhood during the sun's motion in the galaxy. There is now considerable evidence for GCR acceleration by shock waves of supernova in active star-forming regions (OB associations) in the galactic spiral arms. During times of passage into star-forming regions increases in the GCR-flux are expected. Recent data from the Spitzer Space Telescope (SST) are shedding light on the structure of the Milky Way and of its star-forming-regions in spiral arms. Records of flux variations may be found in solar system detectors, and iron meteorites with GCR-exposure times of several hundred million years have long been considered to be potential detectors (Voshage, 1962). Variable concentration ratios of GCR-produced stable and radioactive nuclides, with varying half-lives and therefore integration times, were reported by Lavielleet al. (1999), indicating a recent 38% GCR-flux increase. Potential flux recorders consisting of different pairs of nuclides can measure average fluxes over different time scales (Lavielleet al., 2007; Mathew and Marti, 2008). Specific characteristics of two pairs of recorders (81Kr-Kr and129I-129Xe) are the properties of self-correction for GCR-shielding (flux variability within meteorites of varying sizes). The81Kr-Kr method (Marti, 1967) is based on Kr isotope ratios, while stable129Xe is the decay product of the radionuclide129I, which is produced by secondary neutron reactions on Te in troilites of iron meteorites. The two chronometers provide records of the average GCR flux over 1 and 100 million year time scales, respectively.

The concentrations of cosmogenic radionuclides and noble gases in Pitts (IAB) and Horse Creek (ungrouped) provide unambiguous evidence that both irons have a complex exposure history with a first-stage irradiation of 100-600 Myr under high shielding, followed by a second-stage exposure of ?1 Myr as small objects. The first-stage exposure ages of ~100 Myr for Horse Creek and ~600 Myr for Pitts are similar to cosmic-ray exposure ages of other iron meteorites, and most likely represent the Yarkovsky orbital drift times of irons from their parent bodies in the main asteroid belt to one of the nearby chaotic resonance zones. The short second-stage exposure ages indicate that collisional debris from recent impact events on their precursor objects was quickly delivered to Earth. The short delivery times suggests that the recent collision events occurred while the precursor objects of Horse Creek and Pitts were either very close to the chaotic resonance zones or already in Earthcrossing orbits. Since the cosmogenic noble gas records of Horse Creek and Pitts indicate a minimum radius of a few meters for the precursor objects, but do not exclude km-sized objects, we conclude that these irons may represent fragments of two near-Earth asteroids, 3103 Eger and 1986 DA, respectively. Finally, we used the cosmogenic nuclide concentrations in Horse Creek, which contains 2.5 wt% Si, to test current model calculations for the production of cosmogenic 10Be, 26Al, and neonisotopes from iron, nickel, and silicon.

We measured integral thin target cross sections for the proton-induced production of 3He, 4He, 21Ne, 22Ne, 36Ar and 38Ar from Fe and Ni from the respective reaction thresholds up to 1.6 GeV. The production of noble gas isotopes, especially 4He, from Fe and Ni is of special importance for design studies of accelerator driven systems and/or energy amplifier, because Fe is the main structural material in almost every design study. Furthermore, the cross sections are needed to establish the first physical model calculations for the production of cosmogenic nuclides in iron meteorites. As a result of our new measurements there now exist for both target elements a complete and consistent database for the production of noble gas isotopes. The experimental data are compared to results from the theoretical nuclear model codes INCL4/ABLA and TALYS. This comparison clearly demonstrates again that experimental data are still needed because the predictive power of nuclear model codes, though permanently improving, does still not allow reliably predicting the cross sections needed for most applications and irradiation experiments remain indispensable.

— Two spherical targets made of gabbro with a radius of 25 cm and of steel with a radius of 10 cm were irradiated isotropically with 1600 MeV protons at the SATURNE synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay, in order to simulate the production of nuclides in meteorites induced by galactic cosmic-ray protons in space. These experiments supply depth-dependent production rate data for a wide range of radioactive and stable isotopes in up to 28 target elements. In this paper, we report results for 78Kr, 80–86Kr isotopes in Rb, Sr, Y and Zr and for 124Xe, 126Xe, 128–132Xe, 134Xe, 136Xe isotopes in Ba and La. Krypton and xenon concentrations have been measured at different depths in the spheres by using conventional mass spectrometry. Based on Monte-Carlo techniques, theoretical production rates are calculated by folding depth-dependent spectra of primary and secondary protons and secondary neutrons with the excitation functions of the relevant nuclear reactions. The comparison of the model calculation results with experimental data in the thick target experiments performed at LNS and previously at CERN have allowed adjustments of the poorly known excitation functions of neutron-induced reactions. Thus, for the two experiments at SATURNE, excellent agreement is obtained between experimental and calculated production rates for most Kr and Xe isotopes in all investigated target elements. Only Xe production in Ba in the gabbro is underestimated by the calculations by ˜25%. This work validates the approach of the thin-target model calculations of cosmogenic nuclide production rates in the attempt of modeling the interaction of galactic cosmic-ray protons with stony and iron meteorites in space as well as with lunar samples.

Nitrogen concentrations and isotopic signatures have been determined in groups IIE and IVA iron meteorites. Contrary to assumptions made in the literature, the present data show that spallation components significantly modify the N signatures of the metal. All 15N data are corrected for cosmic-ray produced spallation components using 21Ne concentrations measured in aliquots. A production-rate ratio 21Ne/15N = 0.80 is obtained, which can reliably be used for this correction, since it is not sensitive to shielding differences. The trapped N signatures in group IVA irons fall into two subgroups IVA (−26) with δ15N = −26 ± 2 ‰ and IVA (−6) with δ15N = −6 ± 1.4‰, respectively. Only the latter is close to values reported for metal of L-chondrites. Group IIE irons also define two distinct subgroups IIE (Y) with δ15N = −7.5 ± 1.5‰ and IIE (O) with δ15N = −2.3 ± 1‰. Therefore, the earlier proposed subdivision of IIE irons into “young” and “old” subgroups is substantiated by the different trapped N signatures. With regard to a possible relationship with H-chondrites as suggested by oxygen isotopes, only the young IIE subgroup overlaps the range of signatures reported in H-chondrite metal. Seymchan has a distinctly lighter signature (δ15N = −54‰), consistent with its reclassification as an ungrouped iron. We observe no correlation of either nitrogen concentrations or isotopic signatures with abundances of Ga, Ge, Ir or Ni. The distinct N components in the so-called magmatic group IVA constrain the thermal history of the parent body, as these signatures need to be reconciled with the magmatic history. Implications for the origin of nitrogen components are discussed. Some of the spread in N isotopic data in the literature apparently is due to inclusions.

This is the first contribution towards a reevaluation of exposure histories of iron meteorites and of the constancy of the cosmic ray flux over the last billion years, as recorded in these fossil detectors. We have performed new 36Cl, 26Al, 10Be, and noble gas measurements, including determination of the shielding parameter, S = 4He/21Ne, in samples with published K data. The K isotopic data, coupled to 36Ar and 36Cl concentrations permit selection of meteorites which have only experienced simple (constant geometry) irradiation histories. These objects can be used for the calibration of shielding-dependent production rates within these metallic detectors. In order to carry out production rate calibrations based on 40K–41K data, we assume constancy of the cosmic flux during the interval 150 to 700 My ago. We note that meteorites with very old potassium ages cannot be included in this calibration, as these meteorites require distinct parameter sets. A calibration data set representing a total of 13 meteorites was used to compute long-term (0.5 Gy) average production rates. These average production rates of 36Cl from this particular calibration set are significantly (28%) lower than those determined for the recent (≤10 My) cosmic ray flux. We also document here the quality of the resulting potassium production rate parameter M0(S) with a calculated isochron for irons of group IVA.

— The L/LL5 chondrite Knyahinya had an approximately spherical shape, and as it experienced a single stage exposure history, it represents a very interesting object to study depth profiles of cosmic-ray-produced nuclide concentrations. Such data are required to improve and to validate model calculations of production rates. We report Ne, Ar, Kr and Xe isotopic abundances in five bulk samples. The adopted procedure of noble gas extraction included two pyrolysis steps at 450 °C and 650 °C, respectively, followed by a combustion step in pure O2 at 650 °C before melting the sample. This procedure allows for the separation of a significant fraction of the trapped Kr and Xe, leading to an enrichment of the cosmic-ray produced component, which is released in the melting step. The isotopic composition of the trapped Xe component measured in the combustion step is found to be identical with the OC-Xe composition (Lavielle and Marti, 1992) and supports the suggestion that ordinary chondrites formed in a homogeneous trapped noble gas reservoir. Cosmic-ray produced Kr and Xe components and depth profiles were measured, including for the first time a 81Kr profile. The calculated exposure age of 39.5 ± 1.0 Ma, based on the 81Kr-Kr method, is found to be in excellent agreement with previous determinations. The concentrations of trapped and fissiogenic noble gas components are clearly lower than those generally observed in type 5 ordinary chondrites and may suggest diffusion losses before a meter-sized object was exposed to the cosmic radiation.

The purpose of this work is to study the diffusion properties in an argillaceous formation and how these properties change after the excavation of galleries, over a long period. The Tournemire Underground Research Laboratory (URL) located in Aveyron (France) offers the unique opportunity to investigate different stages of the evolution of the so-called Excavation Damaged Zone (EDZ) over a period of about 124 a. Four horizontal boreholes parallel to the bedding and one vertical borehole were drilled in order to study diffusion transport in the EDZ in both directions in galleries excavated 124, 13, 6, and 1 a ago, respectively. Noble gases dissolved in the pore water of 47 core samples were extracted in order to establish precise depth profiles. Mainly produced in situ by decay of U and Th, radiogenic He accumulates in the pore water of rocks and escapes toward the gallery, allowing a characterization of the diffusive transport in the EDZ and its evolution with time. For the oldest gallery (1882–1888), core mapping reveals an EDZ well developed with fractures up to a depth of 1.8 m. In this zone, all radiogenic He has been lost and at the same time heavy noble gases are trapped in the rock with an enrichment of Xe relative to Kr and of Kr relative to Ar. From 1.8 m, He concentration increases with depth to reach a plateau at about 3.5 m corresponding to a concentration normally found in the unaltered zone. Considering diffusive transport of the radiogenic He to the EDZ, model calculations allowed proposing transport properties in the unfractured and undisturbed zone (UZ) with a pore diffusion coefficient Dp of 1 × 10 −10 m 2 /s deduced from the best-fit curve to experimental data and a mean porosity of 0.1 obtained form petrophysical measurements. The most recent gallery (2008) did not show any evidence of EDZ at depths greater than 7.5 cm. A fracture located around 0.75 m, possibly of tectonic origin, induced large advection and diffusion losses of He on both sides in the next 50 cm. Excesses of Ar, Kr and Xe are found, suggesting diffusion of air from the gallery associated with He losses. The 6-a-old gallery is clearly influenced by fractures of tectonic origin increasing the EDZ thickness of 0.7 m up to a Damaged Zone of 1.8 m. Based on the He concentration profile, the 13-a-old gallery (1996) has a net EDZ of 1.2 m, larger than the 0.7 m deduced from the structural analysis by core mapping, followed by a disturbed zone of up to 3.5 m that could represent an intermediate stage before the development of fractures in the EDZ. The vertical borehole drilled in the same gallery shows a less extensive damaged zone (1.4 m) and allows the determination of a Dp of 3 × 10 −11 m 2 /s taking into account the anisotropy relative to the stratification plane. The rare gas analysis has, therefore, enabled confirmation and better description of the net time-dependent evolution of the EDZ around drifts in the argillaceous Tournemire site: no obvious EDZ for the 1-a gallery (2008), 1.2 m width for the 13-a-old gallery (1996), and 2 m width for the century-old tunnel. The occurrence of a disturbed and unfractured zone (dZ) around the 13-a-old gallery undetected by structural studies and geophysical methods clearly demonstrates the power of radiogenic He in assessing the transport properties around drifts excavated at different ages in compacted clay rocks.

The 140-m-thick, clay-rich Callovo-Oxfordian (COX) layer of the eastern Paris Basin, France, is being considered by the French Nuclear Waste Agency (Andra) as a long-term underground nuclear waste repository. Andra has selected a 250 km2 area (transposition zone) to be further characterised, especially in view of the confinement properties exhibited by the COX. This study reports the helium concentrations and isotopic ratios of water samples from the aquifers above and below the COX, which are the Oxfordian and Dogger aquifers, respectively. The samples were collected from five drilling sites (2007–2008). Both the Oxfordian and Dogger groundwaters are of meteoric origin and have accumulated radiogenic He with a 3He/4He ratio of approximately 0.02 Ra. The He concentrations in the groundwaters are two orders of magnitude higher than in the air-saturated water in the Oxfordian and approximately 10 times higher in the Dogger than in the Oxfordian. One borehole was drilled down into the Triassic sediments, allowing a sample to be collected from the Bundsandstein aquifer. Here, the He concentration is of the same order of magnitude as those measured in the Dogger, but the isotopic ratio is slightly higher at 0.04 Ra. However, this ratio is approximately 10 times lower than those measured by Marty et al. (2003) in waters collected closer to the Trias recharge and tagged with mantle-derived He. This lower ratio is most likely due to a significant and rapid slowdown of the circulation in this aquifer, allowing substantial radiogenic He accumulation. A key conclusion of this study concerns the lateral non-homogeneity of the studied area: He concentrations are higher in the northern part of the transposition zone. This observation can be explained by a longer residence time of the waters and/or a higher input of He from the basement. A simplified 2D model of He transport shows that the second hypothesis alone does not allow fitting of the data, thus implying more stagnant water in this area. The indicative residence times derived from this coarse model are 0.3–0.5 Myr (Oxfordian) and 0.5–0.6 Myr (Dogger) for the borehole located in the centre of the investigated zone; for the northernmost borehole, they reach 0.8–1.4 Myr for the Oxfordian and 1.5 Myr for the Dogger.

— Possible evidence for the presence of 248Cm in the early Solar System was reported from fission gas studies (Rao and Gopalan, 1973) and recently from studies of very high nuclear track densities (≥ 5 × 10g cm−2) in the merrillite of the H4 chondrite Forest Vale (F. V.) (Pellas et al., 1987). We report here an analysis of the isotopic abundances of xenon in F. V. phosphates and results of track studies in phosphate/pyroxene contacts. The fission xenon isotopic signature clearly identifies 244Pu as the extinct progenitor. We calculate an upper limit 248Cm/244Pu < 1.5 × 10−3 at the beginning of Xe retention in F. V. phosphates. This corresponds to an upper limit of the ratio 248Cm/235U ≤ 5 × 10−5, further constraining the evidence for any late addition of freshly synthesized actinide elements just prior to Solar System formation. The fission track density observed after annealing the phosphates at 290 °C (1 hr, which essentially erases spallation recoil tracks) is also in agreement with the 244Pu abundance inferred from fission Xe. The spallation recoil tracks produced during the 76 Ma cosmic-ray exposure account for the very high track density in merrillites.

$\beta$-Thorium phosphate diphosphate polycrystalline ceramic is considered as a promising candidate for the immobilization of actinides in the field of a long-term storage. In order to study the behavior of the ceramic in relation with the evacuation of helium produced by actinides and daughters disintegrations, the release of radiogenic helium from a sintered pellet aged over an about six year period was studied by thermal desorption and high resolution mass spectrometry. The apparent diffusion coefficients are determined for different annealing sequences and are approximately the same for zircon and britholite at low temperature and uranium dioxide ceramic at high temperature. The apparent diffusion coefficients are found to be (7 ± 3) x 10^-22 m^2 s^-1 and (1.5 ± 0.5) · 10^-20 m^2 s^-1 at 20 °C and 120°C, respectively. The activation energy for the apparent diffusion process encompassing both volume and inter-granular diffusion is estimated at 45 ± 15 kJ mol^-1 in the studied temperature range (20–1020° C).

We measured integral thin target cross sections for the proton-induced production of He-, Ne-, and Ar- isotopes from Fe and Ni and of He-, Ne-, Ar-, Kr-, and Xe-isotopes from Bi from the respective reaction thresholds up to 2.6GeV. Iron and Ni are important structural materials for the planned ADS/EA systems and Bi is a major constituent for planned spallation neutron sources. In addition, we give new data for the production of 3 He from Mg, Al, Si, and Pb by revising earlier data and considering now 3 Hd iffusive losses and new information for the 3 H/ 3 He branching ratios. The data are compared to results from theoretical nuclear model codes.

— The Campos Sales meteorite fell close to the town of Campos Sales in the northeastern Brazilian state of Ceara (7°2′ S, 40°10′ W) on 1991 January 31 at 10:00 P.M. (local time). Several fragments were recovered from an area estimated to be 1 × 3 km. The stone is an ordinary L5 chondrite (Fa25.0 and FS21.6) and is lightly shocked (S1). Metal phases present are kamacite, tetrataenite, and antitaenite. Noble gases He, Ne, Ar, Kr, and Xe have been analyzed in two bulk samples of Campos Sales. All exposure ages based on determination of cosmogenic 3He, 21Ne, 38Ar, 83Kr, and 126Xe abundances and on the cosmogenic 81Kr/83Kr ratio agree well, which suggests no gas loss during cosmic-ray exposure. The cosmic-ray exposure age is 23.3 ± 1.0 Ma, which falls in the range observed for L5 chondrites (20–30 Ma). The gas-retention ages indicate He loss that must have occurred prior to or during ejection from the L-chondrite parent body.

Dr. W. Wei, at UCSD, provided our laboratory with chips from a suspected iron meteorite. The mass (>10 kg) was found approximately 8 northwest of Zhongshan in Guangxi province by a farmer in his fields. This mass has now been identified as an IAB iron meteorite (provisional name Zhongshan No.1) based on its composition, N signature, and petrographic analysis. A second chip from a much larger mass (Zhongshan No.2), still in the ground, was recently made available and work is in progress on it, but not reported. Preliminary N isotopic analysis on Zhongshan sample No.1 suggested that the iron mass might be a IAB/IIICD type. Petrographic inspection and INAA analysis has verified that this sample is a typical member of the coarse octahedrites, of the resolved chemical group IAB. Zhongshan No.1 was well-shielded. Its estimated CRE age is {ge}440 Ma. Determination of the radionuclides and noble gases on Zhongshan sample No.2 (in progress) will give useful information on the exposure and shielding history of the meteoroid and its possible atmospheric break-up.

A trapped component of heavy noble gates representing a distinct solar system (presumably asteroid belt) reservoir is known to be concentrated in carbonaceous carriers of chondritic meteorites. The isotopic signature of trapped Xe in separates of the H4 chondrite Forest Vale (FV) was determined by combusting its carrier phases at 600 C in oxygen, discriminating against in situ produced nucleogenic components which are released above 600 C. The isotopic abundances of FV combustion-Xe (FVC-Xe) are compared to signatures of bulk trapped Xe in chondritic meteorites. We conclude that FVC-Xe represents the predominant trapped component in ordinary chondrites (OC) for which we adopt the term OC-Xe. Its isotopic signature differs from Xe in ureilites, in 'average carbonaceous chondrites', in earth's atmosphere, and in the solar wind. Additional minor Xe components were identified in type 3 chondrites and in the metal phase of chondrites. We discuss relationships among solar system Xe reservoirs and show that OC-Xe signature is consistent with a mixture of HL-Xe with slightly mass fractionated solar-type Xe.

Neutron-irradiated targets of natural magnesium have been analyzed by mass spectrometry in order to determine the excitation functions of neon from the energy threshold up to 20 MeV. Production cross sections of {sup 20,21,22}Ne isotopes were measured at 5.20, 7.00, 16.20, and 19.05 MeV.

We report xenon isotopic abundances observed in the stepwise release of noble gases in a highpurity metal separate of the Forest Vale (H4) chondrite. We identify a 244Pu-derived fission component, due to recoils into the metal, a cosmic-ray-produced spallation component and a new trapped component (FVM; 132Xe: 134Xe: 136Xe = 3.16:1.235:1.000) which is isotopically distinct from known solar system reservoirs. We discuss several processes which might account for observed isotopic shifts and conclude that the signature of FVM xenon may provide clues regarding the origin of chondritic metal.

Excitation functions of all stable or long-lived krypton isotopes were measured or estimated for incident protons and neutrons in Rb, Sr, Y, and Zr targets. Experimental data concern mostly Y and Zr targets bombarded with 0.059 to 24 GeV protons. The products /sup 78en-dash86/Kr, /sup 74/As, /sup 75/Se, /sup 83,84,86/Rb, /sup 85/Sr, /sup 88/Y, /sup 88,95/Zr, and /sup 92/Nb/sup m/ were measured using high-sensitivity mass spectrometry and nondestructive ..gamma.. counting. Lighter products such as /sup 38,39,42/Ar and 12 radioactive isotopes from /sup 7/Be to /sup 65/Zn were also measured in some cases and their cross sections are given in an appendix. Most excitation functions pass through a maximum between 0.4 and 0.8 GeV, and the peak energy could depend on the ..delta..A value. The results, combined with a general survey of nuclear reactions in Ga to Nb targets, permitted the development of new systematics leading to the calculation of spallation-produced Kr isotopes in the moon bombarded with galactic and solar cosmic rays. Compared to cosmogenic krypton measured in nine well-documented lunar samples, /sup 83/Kr is predicted with a precision better than 33% (1sigma) and the production ratios /sup i/Kr//sup 83/Kr are predicted to better than 25%. It is concluded thatmore » the cosmogenic ratios /sup 86/Kr//sup 83/Kr and /sup 81/Kr//sup 83/Kr are dependent on the main target element concentrations. This should be taken into account in strontium-rich samples when calculating exposure ages of extra-terrestrial materials.« less

Cosmogenic krypton in iron meteorites arises from the bombardment of the elements between Zr(Z = 40) and Pd(Z = 46) by primary and secondary cosmic rays. In this work we measured the cross-sections of 78- 86Kr formation in nuclear reactions induced by the proton bombardment of Pd and Ag at 0.15, 0.6 (Ag only), 1.05 and 24 GeV using high-sensitivity mass-spectrometry. We then developed a Rudstam-like semi-empirical spallation formula that gives good results in the target and product region of interest Of over about 500 cross-sections compiled for Y(Z = 39) up to Ag(Z = 47) with 5 ≤ Δ A- ≤ 40 and Ep ≽ 130 MeV, 89 % are calculated to better than a factor of 2. That percentage increases to 96 % when excluding small cross sections (σ ≤ 0.1) mb and low energies (Ep ≤ 206 MeV). Our formula is suitable for the calculation of unknown Kr cross-sections in Mo, Ru and Rh, the elements that make the main contribution to cosmogenic krypton in iron meteorites.