Search results for "Pluton"
showing 10 items of 80 documents
Nuclear Forensics: A methodology applicable to Nuclear Security and to Non-Proliferation
2011
Nuclear Security aims at the prevention and detection of and response to, theft, sabotage, unauthorized access, illegal transfer or other malicious acts involving nuclear material". Nuclear Forensics is a key element of nuclear security. Nuclear Forensics is defined as a methodology that aims at re-establishing the history of nuclear material of unknown origin. It is based on indicators that arise from known relationships between material characteristics and process history. Thus, nuclear forensics analysis includes the characterization of the material and correlation with production history. To this end, we can make use of parameters such as the isotopic composition of the nuclear material…
Fission fragment anisotropy for the 242mAm fission isomer by spin exchange pumping with polarized rubidium vapour
1992
Abstract The foundations of an experiment have been worked out with which, in principle, the spin, hyperfine constants and the isomer shift of the 14 ms fission isomer 242mAm can be measured. Such an experiment would be based on the fission fragment anisotropy signal which has actually been observed in this work after spin exchange pumping with polarized rubidium vapour in an optical buffer gas cell. A decrease of the count rate of (12±4)% has been measured at 90% with respect to the quantization axis. From this result it is concluded that the nuclear spin of the 242mAm fission isomer must be larger than 1. The low-energy fission isomers originating from the 242Pu(d, 2n)242mAm reaction have…
Fast-neutron-induced fission cross section of Pu242 measured at the neutron time-of-flight facility nELBE
2019
The fast-neutron-induced fission cross section of $^{242}\mathrm{Pu}$ was measured at the neutron time-of-flight facility $n$ELBE. A parallel-plate fission ionization chamber with novel, homogeneous, large-area $^{242}\mathrm{Pu}$ deposits on Si-wafer backings was used to determine this quantity relative to the IAEA neutron cross-section standard $^{235}\mathrm{U}(n,f)$ in the energy range of 0.5 to 10 MeV. The number of target nuclei was determined from the measured spontaneous fission rate of $^{242}\mathrm{Pu}$. This helps to reduce the influence of the fission fragment detection efficiency on the cross section. Neutron transport simulations performed with geant4, mcnp6, and fluka2011 ar…
Production of plutonium tracers in 237Np nuclear reactions with 3He-ions in the energy range from 26 to 60 MeV
1998
Cross-sections for the reaction Np-237 + He-3 --> Pu-236,Pu-237,Pu-238 at He-3 bombarding energies from 26 to 60 MeV were measured. Thick-target yields, based on the measured and previously known cross-sections were constructed. The results are discussed and compared with Ether reactions leading to the formation of the same final nuclei. (C) 1998 Elsevier Science S.A.
Early Pan-African evolution of the basement around Elat, Israel,and the Sinai Peninsula revealed by single-zircon evaporation dating, and implication…
1990
We report 2<r7Pb/206Pb single-zircon evaporation ages for early Pan-African rocks from southern Israel and the northeastern Sinai Peninsula, the northernmost extension of the Arabian-Nubian shield. The oldest rocks are metamorphic schists of presumed island-arc derivation; detrital zircons date the source terrain at ca. 800-820 Ma. A major phase of tonalite-trondhjemite plutonism occurred at ca. 760-780 Ma; more evolved granitic rocks were emplaced at about 745 Ma. A metagabbro-met adiorite complex reflects the youngest igneous phase at ca. 640 Ma. We Find no evidence for pre-Pan-African crust, and our data document important crust-forming events that correlate with similar episodes elsewhe…
Constraints on Earth accretion deduced from noble metals in the oceanic mantle
1998
If the Earth's mantle were in equilibrium with its core, the mantle would contain three orders of magnitude less of the noble metals (platinum-group elements Pt, Os, Ir, Ru, Pd and Rh, plus Au and Re) than are observed. An explanation put forward to account for this disparity has been that the last 1% of the Earth's accretion occurred after the iron-rich core had separated from the mantle1,2. Recent debate has accordingly centred on which meteorite class or classes made up this ‘late veneer’ of accretion3. Here we present analyses of noble-metal concentrations in oceanic peridotites (plutonic rocks which are thought to represent samples of the Earth's upper mantle). We find that the average…
Chapter 5.2 The Ancient Gneiss Complex of Swaziland and Environs: Record of Early Archean Crustal Evolution in Southern Africa
2007
Publisher Summary This chapter discusses the record of early Archean crustal evolution in Southern Africa. Southern Africa preserves one of the most complete and detailed records of early Precambrian crustal evolution, and the Ancient Gneiss Complex (AGC) of Swaziland and the related rocks along the southern margin of the 3.5–3.2 Ga Barberton Greenstone Belt (BGB) have played a prominent role in models for the early evolution of continental crust. The AGC is separated from the BGB by a large granitoid sheet-like pluton some 3 Ga in age and known as the Mpuluzi Batholith. In northwest Swaziland, however, small inliers of AGC gneisses occur in faulted and sheared contact with BGB rocks, and t…
Zircon ages and Hf isotopic compositions of plutonic rocks from the Central Tianshan (Xinjiang, northwest China) and their significance for early to …
2014
We present new zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the crustal evolution of the Chinese Central Tianshan (Xinjiang, northwest China) in the early to mid-Palaeozoic. The Early Ordovician (ca. 475–473 Ma) granitoid rocks have zircon eHf(t) values either positive (+0.3 to +9.5) or negative (−6.0 to −12.9). This suggests significant addition of juvenile material to, and coeval crustal reworking of, the pre-existing continental crust that is fingerprinted by numerous Precambrian zircon xenocrysts. The Late Ordovician–Silurian (ca. 458–425 Ma) rocks can be assigned to two sub-episodes of magmatism: zircon from rocks of an earlier event (ca. 458–442 Ma) has neg…
Geochemistry, single zircon ages and Sm–Nd systematics of granitoid rocks from theGóry Sowie (Owl Mts), Polish West Sudetes: evidence for earlyarc-re…
1998
Granitoid gneisses as well as their migmatitic and anatectic derivates were investigated from theGory Sowie (Owl Mts) Massif of SW Poland in the central West Sudetes. The gneisses and migmatites aretectonically interlayered with paragneisses, and experienced several consecutive tectono-metamorphicevents. Geochemically, the granitoid gneisses are calc-alkaline and similar to orogenic granite suites, whichtherefore lends support to a subduction-related origin. Single zircon Pb–Pb evaporation ages suggest that the gneiss precursors were emplaced between 473 and488 Ma, and most samples analysed contain zircon xenocrysts with minimum ages between 1124 and2620 Ma. An early phase of high-grade met…
Pb–Pb age, stable isotope and chemical composition of Archaean magnesite, Barberton Greenstone Belt, South Africa
2010
International audience; Trace-element, carbon, oxygen and lead-isotope analyses were carried out to determine the formation mode and crystallization age of magnesite from the Budd ultramafic complex of the Archaean Barberton Greenstone Belt, South Africa. Its significantly high Ti contents probably relate to a soluble Ti-rich accessory mineral, probably dissolved during magnesite precipitation. Primitive mantle-normalized REE patterns of the magnesite show negative Ce and Eu anomalies induced by two events: (1) the Eu anomaly indicates reducing conditions probably induced by the emplacement of the ultramafic source rock; (2) the Ce anomaly implies oxidizing conditions, probably during a hyd…