3,402 research outputs found
First Measurement of the 64Ni(gamma,n)63Ni Cross Section
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-Non Commercial-ShareAlike LicenceIn the past 10 years new and more accurate stellar neutron capture cross section measurements have changed and improved the abundance predictions of the weak s process. Among other elements in the region between iron and strontium, most of the copper abundance observed today in the solar system distribution was produced by the s process in massive stars. However, experimental data for the stellar 63Ni(n,gamma)64Ni cross section are still missing, but is strongly required for a reliable prediction of the copper abundances. 63Ni (t1/2 =101.2 a) is a branching point and also bottleneck in the weak s process flow, and abehaves differently during core He and shell C burning. During core He burning the reaction flow proceeds via beta-decay to 63Cu, and a change of the 63Ni(n,gamma)64Ni cross section would have no influence. However, this behavior changes at higher temperatures and neutron densities during the shell C burning phase. Under these conditions, a significant amount of the s process nucleosynthesis flow is passing through the channel 62Ni(n,gamma)63Ni(n,gamma)64Ni. At present only theoretical estimates are available for the 63Ni(n,gamma)64Ni cross section. The corresponding uncertainty affects the production of 63Cu in present s process nucleosynthesis calculations and propagates to the abundances of the heavier species up to A=70. So far, experimental information is also missing for the inverse 64Ni(gamma,n) channel. We have measured for the first time the 64Ni(gamma,n)63Ni cross section and also combined for the first time successfully the photoactivation technique with subsequent Accelerator Mass Spectrometry (AMS). The activations at the ELBE facility in Dresden-Rossendorf were followed by the 63Ni/64Ni determination with AMS at the MLL accelerator laboratory in Garching. First results indicate that theoretical predictions have overestimated this cross section up to now. If this also holds for the inverse channel 63Ni(n,gamma)64Ni, more 63Ni is accumulated during the high neutron density regime of the C shell that will contribute to the final abundance of 63Cu by radiogenic decay. In this case, also a lower s process efficiency is expected for the heavier species along the neutron capture path up to the Ga-Ge regio
Primary Proton Spectrum of Cosmic Rays measured with Single Hadrons
The flux of cosmic-ray induced single hadrons near sea level has been
measured with the large hadron calorimeter of the KASCADE experiment. The
measurement corroborates former results obtained with detectors of smaller size
if the enlarged veto of the 304 m^2 calorimeter surface is encounted for. The
program CORSIKA/QGSJET is used to compute the cosmic-ray flux above the
atmosphere. Between E_0=300 GeV and 1 PeV the primary proton spectrum can be
described with a power law parametrized as
dJ/dE_0=(0.15+-0.03)*E_0^{-2.78+-0.03} m^-2 s^-1 sr^-1 TeV^-1. In the TeV
region the proton flux compares well with the results from recent measurements
of direct experiments.Comment: 13 pages, accepted by Astrophysical Journa
Positron Fraction in the CMSSM
A fit to the present data on the cosmic ray positron fraction can be
considerably improved,if in addition to the positron production by nuclear
interactions in the universe the possible contribution from supersymmetric dark
matter annihilation is taken into account. We scan over the complete SUSY
parameter space of the Constrained Minimal Supersymmetric Model (CMSSM) and
find that in the acceptable regions the neutralino annihilation into b-bbar
quark pairs is the dominant channel with hard positrons emerging from the
semileptonic decays of the B-mesons.Comment: 6 pages, Latex, Proceedings of the 4th International Workshop on
Identification of Dark Matter (idm2002), York, England, 2-6 September, 200
A mobile detector for measurements of the atmospheric muon flux in underground sites
Muons comprise an important contribution of the natural radiation dose in air
(approx. 30 nSv/h of a total dose rate of 65-130 nSv/h), as well as in
underground sites even when the flux and relative contribution are
significantly reduced. The flux of the muons observed in underground can be
used as an estimator for the depth in mwe (meter water equivalent) of the
underground site. The water equivalent depth is an important information to
devise physics experiments feasible for a specific site. A mobile detector for
performing measurements of the muon's flux was developed in IFIN-HH, Bucharest.
Consisting of 2 scintillator plates (approx. 0.9 m2) which measure in
coincidence, the detector is installed on a van which facilitates measurements
at different locations at surface or underground. The detector was used to
determine muon fluxes at different sites in Romania. In particular, data were
taken and the values of meter water equivalents were assessed for several
locations from the salt mine from Slanic Prahova, Romania. The measurements
have been performed in 2 different galleries of the Slanic mine at different
depths. In order to test the stability of the method, also measure- ments of
the muon flux at surface at different elevations were performed. The results
were compared with predictions of Monte-Carlo simulations using the CORSIKA and
MUSIC codes
Lavender oil-potent anxiolytic properties via modulating voltage dependent calcium channels
Recent clinical data support the clinical use of oral lavender oil in patients suffering from subsyndromal anxiety. We identified the molecular mechanism of action that will alter the perception of lavender oil as a nonspecific ingredient of aromatherapy to a potent anxiolytic inhibiting voltage dependent calcium channels (VOCCs) as highly selective drug target. In contrast to previous publications where exorbitant high concentrations were used, the effects of lavender oil in behavioral, biochemical, and electrophysiological experiments were investigated in physiological concentrations in the nanomolar range, which correlate to a single dosage of 80 mg/d in humans that was used in clinical trials. We show for the first time that lavender oil bears some similarities with the established anxiolytic pregabalin. Lavender oil inhibits VOCCs in synaptosomes, primary hippocampal neurons and stably overexpressing cell lines in the same range such as pregabalin. Interestingly, Silexan does not primarily bind to P/Q type calcium channels such as pregabalin and does not interact with the binding site of pregabalin, the α2δ subunit of VOCCs. Lavender oil reduces non-selectively the calcium influx through several different types of VOCCs such as the N-type, P/Q-type and T-type VOCCs. In the hippocampus, one brain region important for anxiety disorders, we show that inhibition by lavender oil is mainly mediated via N-type and P/Q-type VOCCs. Taken together, we provide a pharmacological and molecular rationale for the clinical use of the oral application of lavender oil in patients suffering from anxiety
Opportunities for Nuclear Astrophysics at FRANZ
The "Frankfurter Neutronenquelle am Stern-Gerlach-Zentrum" (FRANZ), which is
currently under development, will be the strongest neutron source in the
astrophysically interesting energy region in the world. It will be about three
orders of magnitude more intense than the well-established neutron source at
the Research Center Karlsruhe (FZK)
Simulation of Atmospheric Muon and Neutrino Fluxes with CORSIKA
The fluxes of atmospheric muons and neutrinos are calculated by a three
dimensional Monte Carlo simulation with the air shower code CORSIKA using the
hadronic interaction models DPMJET, VENUS, GHEISHA, and UrQMD. For the
simulation of low energy primary particles the original CORSIKA has been
extended by a parametrization of the solar modulation and a microscopic
calculation of the directional dependence of the geomagnetic cut-off functions.
An accurate description for the geography of the Earth has been included by a
digital elevation model, tables for the local magnetic field in the atmosphere,
and various atmospheric models for different geographic latitudes and annual
seasons. CORSIKA is used to calculate atmospheric muon fluxes for different
locations and the neutrino fluxes for Kamioka. The results of CORSIKA for the
muon fluxes are verified by an extensive comparison with recent measurements.
The obtained neutrino fluxes are compared with other calculations and the
influence of the hadronic interaction model, the geomagnetic cut-off and the
local magnetic field on the neutrino fluxes is investigated.Comment: revtex, 19 pages, 19 Postscript figures, submitted to Phys. Rev.
Resonant all-electric spin pumping with spin-orbit coupling
All-electric devices for the generation and filtering of spin currents are of
crucial importance for spintronics experiments and applications. Here we
consider a quantum dot between two metallic leads in the presence of spin-orbit
coupling, and we analyze in the frame of a scattering matrix approach the
conditions for generating spin currents in an adiabatically driven two-terminal
device. We then focus on a dot with two resonant orbitals and show by specific
examples that both spin filtering and pure spin current generation can be
achieved. Finally, we discuss the effect of the Coulomb interaction.Comment: 4 pages, corrected typo in list of author
Monte Carlo Simulations of the Transition Radiation Detector of the AMS-02 Experiment
The Transition Radiation Detector of the AMS-02 experiment on the
International Space Station is used for the separation of cosmic-ray positrons
and electrons from protons and anti-protons, and for the identification of
nuclei up to carbon (Z<=6). We present the Geant4 simulation that is used to
describe the ionization and transition radiation processes and compare its
results to flight data from AMS-02. After applying empirical corrections to the
simulated data, the particle energy deposition and likelihood distributions in
the TRD are described with high accuracy.Comment: 7 pages, 9 figures. Accepted for publication in Nuclear Inst. and
Methods in Physics Research, A. CC-BY-NC-ND 4.0 licens
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