74 research outputs found
Calibration of the Isomer Shift for the 35.46 keV Mossbauer Transition of 125Te
開始ページ、終了ページ: 冊子体のページ付
Chemical Effects on lnternal Conversion of Outer-Shell Electrons in 125Te
開始ページ、終了ページ: 冊子体のページ付
Superdeformation in Asymmetric NZ Nucleus Ar
A rotational band with five -ray transitions ranging from 2 to
12 states was identified in Ar. This band is linked through
transitions from the excited 2, 4 and 6 levels to
the low-lying states; this determines the excitation energy and the spin-parity
of the band. The deduced transition quadrupole moment of 1.45 indicates that the band has a superdeformed shape. The nature of the band
is revealed by cranked Hartree--Fock--Bogoliubov calculations and a
multiparticle--multihole configuration is assigned to the band
Search for the Production of Element 112 in the 48Ca + 238U Reaction
We have searched for the production of element 112 in the reaction of 231 MeV
48Ca with 238U. We have not observed any events with a "one event" upper limit
cross section of 1.6 pb for EVR-fission events and 1.8 pb for EVR-alpha events.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
Signature splitting inversion and backbending in 80Rb
High spin states of 80Rb are studied via the fusion-evaporation reactions
65Cu+19F, 66Zn+18O and 68Zn+16O with the beam energies of 75 MeV, 76 MeV and 80
MeV, respectively. Twenty-three new states with twenty-eight new \gamma
transitions were added to the previously proposed level scheme, where the
second negative-parity band is significantly pushed up to spins of 22^{-} and
15^{-} and two new sidebands are built on the known first negative-parity band.
Two successive band crossings with frequencies 0.51 MeV and 0.61 MeV in the
\alpha=0 branch as well as another one in the \alpha=1 branch of the second
negative-parity band are observed for the first time. Signature inversions
occur in the positive- and first negative-parity bands at the spins of 11\hbar
and 15\hbar, respectively. The signature splitting is seen obviously in the
second negative-parity band, but the signature inversion is not observed. It is
also found that the structure of the two negative-parity bands is similar to
that of its isotone ^{82}Y. Signature inversion in the positive-parity yrast
band with configuration \pi g_{9/2} \otimes \nu g_{9/2} in this nucleus is
discussed using the projected shell model (PSM)
The Alvarez impact theory of mass extinction; limits to its applicability and the „great expectations syndrome”
For the past three decades, the Alvarez impact theory of mass extinction, causally related to catastrophic meteorite impacts, has been recurrently applied to multiple extinction boundaries. However, these multidisciplinary research efforts across the globe have been largely unsuccessful to date, with one outstanding exception: the Cretaceous-Paleogene boundary. The unicausal impact scenario as a leading explanation, when applied to the complex fossil record, has resulted in force-fitting of data and interpretations ("great expectations syndrome". The misunderstandings can be grouped at three successive levels of the testing process, and involve the unreflective application of the impact paradigm: (i) factual misidentification, i.e., an erroneous or indefinite recognition of the extraterrestrial record in sedimentological, physical and geochemical contexts, (ii) correlative misinterpretation of the adequately documented impact signals due to their incorrect dating, and (iii) causal overestimation when the proved impact characteristics are doubtful as a sufficient trigger of a contemporaneous global cosmic catastrophe. Examples of uncritical belief in the simple cause-effect scenario for the Frasnian-Famennian, Permian-Triassic, and Triassic-Jurassic (and the Eifelian-Givetian and Paleocene-Eocene as well) global events include mostly item-1 pitfalls (factual misidentification), with Ir enrichments and shocked minerals frequently misidentified. Therefore, these mass extinctions are still at the first test level, and only the F-F extinction is potentially seen in the context of item-2, the interpretative step, because of the possible causative link with the Siljan Ring crater (53 km in diameter). The erratically recognized cratering signature is often marked by large timing and size uncertainties, and item-3, the advanced causal inference, is in fact limited to clustered impacts that clearly predate major mass extinctions. The multi-impact lag-time pattern is particularly clear in the Late Triassic, when the largest (100 km diameter) Manicouagan crater was possibly concurrent with the end-Carnian extinction (or with the late Norian tetrapod turnover on an alternative time scale). The relatively small crater sizes and cratonic (crystalline rock basement) setting of these two craters further suggest the strongly insufficient extraterrestrial trigger of worldwide environmental traumas. However, to discuss the kill potential of impact events in a more robust fashion, their location and timing, vulnerability factors, especially target geology and palaeogeography in the context of associated climate-active volatile fluxes, should to be rigorously assessed. The current lack of conclusive impact evidence synchronous with most mass extinctions may still be somewhat misleading due to the predicted large set of undiscovered craters, particularly in light of the obscured record of oceanic impact events
The earth-moon system during the late heavy bombardment period - geochemical support for impacts dominated by comets
The Late Heavy Bombardment (LHB) period is the narrow time interval between
3.8 and 3.9 Gyr ago, where the bulk of the craters we see on the Moon formed.
Even more craters formed on the Earth.
During a field expedition to the 3.8 Gyr old Isua greenstone belt in
Greenland, we sampled three types of metasedimentary rocks, that contain direct
traces of the LHB impactors by a seven times enrichment (150 ppt) in iridium
compared to present day ocean crust (20 ppt).
We show that this enrichment is in agreement with the lunar cratering rate,
providing the impactors were comets, but not if they were asteroids. Our study
is a first direct indication of the nature of the LHB impactors, and the first
to find an agreement between the LHB lunar cratering rate and the Earth's early
geochemical record (and the corresponding lunar record).
The LHB comets that delivered the iridium we see at Isua will at the same
time have delivered the equivalent of a km deep ocean, and we explain why one
should expect a cometary ocean to become roughly the size of the Earth's
present-day ocean, not only in terms of depth but also in terms of the surface
area it covers.Comment: Accepted for publication in Icaru
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