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Meteoritics 11/1978; 13:541.
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ABSTRACT: The Sm-Nd evolution of Apollo 15 green glass is discussed. The ICE age (intercept with chondritic evolution) of 3.8 + or - 0.4 eons overlaps the range of reported (Ar-39)-(Ar-40) ages and implies a distinct source region for green glass, characterized by very low and unfractionated REE abundances. Evidence is presented that LINd (lunar initial Nd) is compatible with a 'chondritic'-type Nd isotopic evolution as observed in the Juvinas meteorite. This normalization is used to study the Sm-Nd system of various lunar rock types. The results obtained from a limited number of rocks clearly indicate differential Sm-Nd evolution for the lunar crust and mantle. High-Ti basalts returned by the Apollo 11 and 17 missions were derived from distinct source regions. The Nd-143 evolution in KREEP requires a source region which is clearly distinct from any mantle reservoir.
06/1978;
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02/1978; 9:672-674.
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Meteoritics 08/1977; 12:300.
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ABSTRACT: Isotope ratios and age estimations are presented for the ultramafic pyroxenite Angra dos Reis meteorite. A pyroxene-phosphate internal isochron age of 4.55 plus or minus 0.04 eons was obtained, in agreement with reported Pb-Pb ages. It is suggested that Sm-146 decay led to an increase in the ratio of Nd-142 to Nd-144 in pyroxene, which is greater than the ratio of the Nd isotopes in phosphates. The effect of Pu-244 on the fission xenon components in pyroxene and phosphate is examined. The ratios of Pu-244 to Nd, U-238, and Th-232 are compared for pyroxene and phosphate separates. The exposure age of the meteorite, as obtained by the Kr-81 to Kr-83 method, was found to be 55.5 plus or minus 1.2 million years.
07/1977;
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02/1977; 8:619.
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02/1976; 7:509.
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ABSTRACT: The history of lunar troctolite 76535 was investigated on the basis of information from the Sm-147-Nd-143 mineral isochron age, the Nd-143 evolution, extinct Pu-224, the Kr-81-Kr exposure age and the cosmic ray exposure record. It was found that the troctolite minerals last equilibrated 4.26 plus or minus 0.06 AE ago and that the Sm-Nd system became closed at this time. The rock remained at temperatures where the loss of radiogenic Ar-40 was small.
02/1976;
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09/1975;
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02/1975;
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ABSTRACT: The evidence for in situ produced fission xenon from Pu-244 in rock 14321 is presented. The inferred abundance ratio Pu-244/U-238 is found to be consistent with values observed in a meteorite. Data from a stepwise release of the xenon permits a characterization of the trapped component, which can be shown to be distinct from solar xenon. We discuss the evidence for the presence of fission gases and of uncorrelated radiogenic argon in this and in other Apollo 14 rocks and some implications regarding their origin.
09/1973;
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ABSTRACT: The evidence forin situ produced fission xenon from244Pu in rock 14321 is presented. The inferred abundance ratio244Pu/238U is found to be consistent with values observed in a meteorite. Data from a stepwise release of the xenon permits a characterization of the trapped component, which can be shown to be distinct from solar xenon. We discuss the evidence for the presence of fission gases and of uncorrelated radiogenic argon in this and in other Apollo 14 rocks and some implications regarding their origin.
Earth Moon and Planets 02/1973; 8(1):241-250. · 0.67 Impact Factor
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ABSTRACT: Cosmic-ray exposure ages of Apollo 14 rocks and rock fragments obtained by the Kr81-Kr83 method range from 27 to 700 m.y. Rock 14321, collected near the Cone crater rim, is one of the many approximately 27 m.y. old ejecta which were reported at the Third Lunar Science Conference. All the other rocks have considerably higher exposure ages. Isotopic anomalies from neutron capture in gadolinium, bromine, and barium are used to obtain information on the lunar neutron spectrum at various depths below the lunar surface. The flux ratio of resonance and slow (less than 0.3 eV) neutrons is found to be nearly constant in the topmost approximately 100 g/sq cm.
02/1972;
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ABSTRACT: The Gd isotopic composition in 19 lunar rock and soil samples from three Apollo sites is reported. The analytical techniques and the high precision mass spectrometric measurements are discussed. Enrichments in the Gd-158 oxide to G-157 oxide ratio due to neutron capture range up to 0.75%. Integrated 'thermal' neutron fluxes derived from the isotopic anomalies of Gd are compared with spallation Kr data from aliquot samples to construct a model which gives both average cosmic-ray irradiation depths and effective neutron exposure ages for some rocks. Rock 14310 is the first lunar sample where Kr anomalies due to resonance neutron capture in Br are observed. A Kr-81/Kr exposure age of 262 (plus or minus 7)m.y. is calculated for this rock.
01/1972;
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12/1971; 3:495.
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ABSTRACT: Cosmic ray exposure ages and rare gas concentration profiles in Apollo 12 lunar rocks, discussing spallation products and neutron capture effects
02/1971;
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12/1970; 2:62-62.
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ABSTRACT: Apollo 11 lunar soil irradiation history from solar wind rare gas abundances and cosmic ray spallation products
02/1970;
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ABSTRACT: The isotopic abundances of the rare gases in the fines are found to be similar to those previously reported for gas-rich meteorites. Relative to the heavy gases, neon and helium are depleted by factors of 2.5 and 10 respectively. Accurate krypton-krypton ages for rocks 10017, 10047, 10057, and 10071 were obtained covering a range of from 47 to 509 x 10(6) years. Varying relative production rates of the krypton and xenon isotopes in these rocks suggest different irradiation conditions and a complex history for at least some of the rocks.
Science 02/1970; 167(3918):548-50. · 31.20 Impact Factor
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ABSTRACT: The Gd isotopic composition in 19 lunar rock and soil samples from three Apollo sites is reported. The analytical techniques and the high precision mass spectrometric measurements are discussed. Enrichments in158GdO/157GdO due to neutron capture range up to 0.75%. Integrated ‘thermal’ neutron fluxes derived from the isotopic anomalies of Gd are compared with spallation Kr data from aliquot samples to construct a model which gives both average cosmic-ray irradiation depths and effective neutron exposure ages (Tn) for some rocks. In the case of rock 12053, this yields an average sample location of ∼300 g/cm2 below the lunar surface and an effective irradiation age of ∼230 my, compared to 99 my obtained by the81Kr-Kr method. Rock 14310 is the first lunar sample where Kr anomalies due to resonance neutron capture in Br are observed. A81Kr-Kr exposure age of 262 ± 7 my is calculated for this rock.
Earth and Planetary Science Letters.
