Results 1 - 10 of 360
Results 1 - 10 of 360. Search took: 0.02 seconds
|Sort by: date | relevance|
[en] In this paper, the interacting boson model (IBM-1) is discussed and employed for calculating the energy level and the electromagnetic transition probabilities B(E2) of the even - even 174-180Hf isotopes. These isotopes have been investigated based on two different arrangements; i.e., the dynamical symmetry of 176-180Mf isotopes, SU (3) (deformed nuclei) and the dynamical symmetry of 174Hf isotopein transition region SU(30-O(6). The determined values using the IBM-1 Hamiltonian showed significant agreement with the experimentally reported energy level and B(E2) values. The model provides a fast and accurate predication method of energy level B(E2)values. (authors).
[en] The Mora Formation (Narcea Group) is one of the oldest Precambrian supracrustal successions in northern Spain. Here, we use U–Pb and in situ Hf isotope analysis on detrital zircon to determine its age and provenance. The youngest U–Pb dates constrain the maximum depositional age of the Mora Formation at 565 ± 11 Ma. Results indicate: (1) a dominant Ediacaran zircon population (33%; 565–633 Ma, Cadomian) within a spectrum of Neoproterozoic ages (40%; 636–996 Ma); and (2) smaller Mesoproterozoic (5%; 1004–1240 Ma), Palaeoproterozoic (11%; 1890–2476 Ma) and Archean (11%; 2519–3550 Ma) populations. Results here do not point to one specific cratonic source area; instead, detritus may have been derived from the West African craton and Amazonia, or even the concealed Iberian basement. The lack of 1.3–1.8 Ga grains suggests exclusion of the Sahara Craton as a major source, but this is not certain. This mixed composition favours a complex source history with reworking of detritus across terrane/craton boundaries. Hafnium isotope compositions indicate a range of crustal and juvenile sources, with initial εHf values between −15.8 and 11.1, and Hf model ages from 0.8 to 3.7 Ga. For Neoproterozoic zircons (80%), juvenile components (εHf(i) ~+10) may be related to Rodinia fragmentation and the onset of an active margin setting leading to the Cadomian orogeny. Palaeoproterozoic to Paleoarchean grains (20%) all have negative εHf values and Meso- to Eoarchean Hf model ages. This indicates an early (Archean) sialic crustal component for northwestern Gondwana.
[en] In context to determine nuclear parameters of stored hafnium ions with laserspectroscopic methods the isotope shifts of the isotopes with even mass numbers from 172Hf to 180Hf have been measured. The value for the isotope 172Hf and with it the change of the mean square charge radius has been unknown so far. Hafnium ions were stored in a Paul trap for mote than four hours. The advantage in using an ion trap is the small necessary sample size. In the case of hafnium an amount of 10 pg is sufficient. Because of the ion velocity the linewidth of a spectrum is dopplerbroadened. This is mainly due to the applied storage voltage. The spectral resolution is not enough to measure isotope shift and hyperfine structure of hafnium ions. Therefore new methods have been developed to reduce the linewidth by excitation of the ions with light only in definite phases of the applied alternating voltage. The width of the spectra is then reduced to a factor three. The signal strength decreases not more than 50%. (orig.)
[de]Im Rahmen der Bestimmung von Kerngroessen an gespeicherten Hafniumionen mit der Methode der Laserspektroskopie wurde die Isotopieverschiebung der Isotope mit gerader Massenzahl von 172Hf bis 180Hf gemessen. Der Wert fuer das Isotop 172Hf und damit die Aenderung des mittleren quadratischen Kernladungsradius war vorher noch unbekannt. Die Hafniumionen waren in einer Paulschen Ionenfalle gespeichert, die Speicherdauer betrug mehr als vier Stunden. Der grosse Vorteil der Ionenfalle liegt in der geringen erforderlichen Probengroesse, bei Hafnium genuegt eine Ausgangsmenge von 10 pg, um ein Isotop in einer sonst leeren Falle nachweisen zu koennen. Die Linienbreite der Spektren ist dopplerverbreitert durch die Geschwindigkeit der Ionen aufgrund des speichernden Wechselfeldes. Die damit erreichte Aufloesung reicht nicht aus, um bei Hafniumionen die Isotopieverschiebung oder Hyperfeinstruktur-Aufspaltung zu messen. Es wurden deshalb neue Methoden entwickelt, mit denen die Linienbreite reduziert werden kann, indem die Ionen nur in bestimmte Phasen zum speichernden Wechselfeld mit Licht angeregt wurden. Die Breite der Spektren geht dann um einen Faktor drei zurueck, die Signalrate nimmt dabei hoechstens um die Haelfte ab. (orig.)
[en] In this study, we present detrital zircon U--Pb ages and Hf isotopic data and whole-rock geochemical data from meta-sedimentary rocks of the Jiangyu Group in eastern Jilin Province (Northeast China) to constrain the late Silurian -- Early Devonian tectonic evolution of the southeastern Xing'an--Mongolia Orogenic Belt. Two samples of the meta-sedimentary rocks from the Jiangyu Group yielded concordant ages ranging from 2926 to 415 Ma, and the youngest zircon populations of the two samples yielded weighted mean ages of 427 ± 3 and 426 ± 3 Ma, respectively. Combined with reliable published muscovite 40Ar-39Ar ages of 408 Ma from the overlying metamorphic ophiolitic melange, these data indicate that the protoliths of the Jiangyu Group were deposited during the late Silurian-Early Devonian Era. A comparison of the U-Pb ages and Hf isotopic data for detrital zircons from northeastern Gondwana and the Jiangyu Group indicates a probable tectonic affinity. The whole-rock geochemical data indicate that the protoliths of the meta-sedimentary rocks from the Jiangyu Group were graywackes deposited in a continental arc setting. Based on the recognition of the early to middle Paleozoic subduction-accretion events along the eastern segment of the northern margin of the North China Craton (NCC), we infer that the subduction-accretion events may have occurred in the Yanbian area followed by one or more arc-continent collisions after the Early Devonian. (author)
[en] The deformation properties of two isotopic chains Yb and Hf from neutron deficient up to neutron drip lines using an axially deformed relativistic mean field (RMF) formalism were studied. A change in sign of ground state hexadecapole moments from positive to negative value at A=180 and again from negative to positive at A=198 for Hf isotopes with TM1 parameter set is found at A=178 and A=196 from positive to negative and negative to positive values respectively
[en] We discuss some characteristic features of the wobbling motion excited on the triaxial superdeformed Lu and Hf nuclei. We show these features are determined by the behavior of the moments of inertia
[en] Geodynamic evolution in the late Paleozoic is significant for understanding the final amalgamation of the Central Asian Orogenic Belt (CAOB). No consensus has yet been reached regarding the late Paleozoic geodynamic evolution of the northern Great Xing’an Range (GXR) in northeastern China, the eastern CAOB. Furthermore, late Paleozoic syenogranite- diabase dyke association is present in the Xiaokele area in northern GXR. It provides an important opportunity to understand the nature of magmatism and the geodynamic evolution during this period. This paper presents new zircon U-Pb ages, zircon Hf isotopic compositions, and geochemical data of whole rocks for Xiaokele syenogranite and diabase. Zircon U-Pb dating suggests that the Xiaokele syenogranite (292.5 ± 0.9 Ma) and diabase (298.3 ± 1.5 Ma) were emplaced during the early Permian. The Xiaokele syenogranites have high SiO2 contents, low MgO contents, and enriched zircon εHf(t) values, suggesting that their primary magma was generated by the partial melting of the juvenile crustal material. The Xiaokele diabases have low SiO2 contents, high MgO contents, are enriched in large-ion lithophile elements, depleted in high-field-strength elements, and exhibit enriched zircon εHf(t) values. They derived from a lithospheric mantle source that had previously been metasomatized by slab-derived fluids. Combined with previous research results, we believe that the continent-continent collision between the Xing’an and Songliao blocks occurred during the late early Carboniferous - early late Carboniferous (330-310 Ma), and the two blocks were transformed into a post-collisional extensional setting during the latest Carboniferous - early Permian. (author)
[en] The s-process nucleosynthesis of the isobar pair 176Lu/176Hf, a long-lived cosmic clock, is examined in conjunction with the s-only isotopes /sup 148,150/Sm, 154Gd, 160Dy, 170Yb, 186Os, and 192Pt. Expressions are derived which allow us to calculate the s-process age from measured quantities alone. A formula is specified which does not contain the population probability P to the 3.68 hr isometric state in 176Lu. This allows us to decide if 176Lu is, in addition to a cosmic clock, also a stellar thermometer