73 research outputs found
Description of dipole strength in heavy nuclei in conformity with their quadrupole degrees of freedom
In conformity to new findings about the widespread occurrence of triaxiality
arguments are given in favor of a description of the giant dipole resonance in
heavy nuclei by the sum of three Lorentzians. This TLO parameterization allows
a strict use of resonance widths {\Gamma} in accordance to the theoretically
founded power law relation to the resonance energy. No additional variation of
{\Gamma} with the photon energy and no violation of the sum rule are necessary
to obtain a good agreement to nuclear photo-effect, photon scattering and
radiative capture data. Photon strength other than E1 has a small effect, but
the influence of the level density on photon emission probabilities needs
further investigation.Comment: Presented at the 3rd International Workshop on Compound Nuclear
Reactions and Related Topics at Prague, 2011, to be published via the EPJ Web
of Conference
Strength of the =1.842 MeV resonance in the Ca(p,)Sc reaction revisited
The strength of the MeV resonance in the
Ca(p,)Sc reaction is determined with two different
methods: First, by an absolute strength measurement using calcium hydroxide
targets, and second, relative to the well-determined strength of the resonance
triplet at = 4.5 MeV in the Ca(,)Ti
reaction. The present new value of eV is 37%
(equivalent to ) higher than the evaluated literature value. In
addition, the ratio of the strengths of the 1.842 MeV
Ca(p,)Sc and 4.5 MeV
Ca(,)Ti resonances has been determined to be
. The newly corrected strength of the 1.842-MeV resonance can
be used in the future as a normalization point for experiments with calcium
targets.Comment: Submitted to Phys. Rev.
Neutron total cross section measurements of gold and tantalum at the nELBE photoneutron source
Neutron total cross sections of Au and Ta have been
measured at the nELBE photoneutron source in the energy range from 0.1 - 10 MeV
with a statistical uncertainty of up to 2 % and a total systematic uncertainty
of 1 %. This facility is optimized for the fast neutron energy range and
combines an excellent time structure of the neutron pulses (electron bunch
width 5 ps) with a short flight path of 7 m. Because of the low instantaneous
neutron flux transmission measurements of neutron total cross sections are
possible, that exhibit very different beam and background conditions than found
at other neutron sources.Comment: article (18 pages, 10 figures, 2 tables) with attached data tables
(13 pages
The new Felsenkeller 5 MV underground accelerator
The field of nuclear astrophysics is devoted to the study of the creation of
the chemical elements. By nature, it is deeply intertwined with the physics of
the Sun. The nuclear reactions of the proton-proton cycle of hydrogen burning,
including the 3He({\alpha},{\gamma})7Be reaction, provide the necessary nuclear
energy to prevent the gravitational collapse of the Sun and give rise to the by
now well-studied pp, 7Be, and 8B solar neutrinos. The not yet measured flux of
13N, 15O, and 17F neutrinos from the carbon-nitrogen-oxygen cycle is affected
in rate by the 14N(p,{\gamma})15O reaction and in emission profile by the
12C(p,{\gamma})13N reaction. The nucleosynthetic output of the subsequent phase
in stellar evolution, helium burning, is controlled by the
12C({\alpha},{\gamma})16O reaction.
In order to properly interpret the existing and upcoming solar neutrino data,
precise nuclear physics information is needed. For nuclear reactions between
light, stable nuclei, the best available technique are experiments with small
ion accelerators in underground, low-background settings. The pioneering work
in this regard has been done by the LUNA collaboration at Gran Sasso/Italy,
using a 0.4 MV accelerator.
The present contribution reports on a higher-energy, 5.0 MV, underground
accelerator in the Felsenkeller underground site in Dresden/Germany. Results
from {\gamma}-ray, neutron, and muon background measurements in the
Felsenkeller underground site in Dresden, Germany, show that the background
conditions are satisfactory for nuclear astrophysics purposes. The accelerator
is in the commissioning phase and will provide intense, up to 50{\mu}A, beams
of 1H+, 4He+ , and 12C+ ions, enabling research on astrophysically relevant
nuclear reactions with unprecedented sensitivity.Comment: Submitted to the Proceedings of the 5th International Solar Neutrino
Conference, Dresden/Germany, 11-14 June 2018, to appear on World Scientific
-- updated version (Figure 2 and relevant discussion updated, co-author A.
Domula added
The resonance triplet at E_alpha = 4.5 MeV in the 40Ca(alpha,gamma)44Ti reaction
The 40Ca(alpha,gamma)44Ti reaction is believed to be the main production
channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation
from decaying 44Ti has been observed so far for two supernova remnants, and a
precise knowledge of the 44Ti production rate may help improve supernova
models. The 40Ca(alpha,gamma)44Ti astrophysical reaction rate is determined by
a number of narrow resonances. Here, the resonance triplet at E_alpha = 4497,
4510, and 4523 keV is studied both by activation, using an underground
laboratory for the gamma counting, and by in-beam gamma spectrometry. The
target properties are determined by elastic recoil detection analysis and by
nuclear reactions. The strengths of the three resonances are determined to
omega gamma = (0.92+-0.20), (6.2+-0.5), and (1.32+-0.24) eV, respectively, a
factor of two more precise than before. The strengths of this resonance triplet
may be used in future works as a point of reference. In addition, the present
new data directly affect the astrophysical reaction rate at relatively high
temperatures, above 3.5 GK.Comment: 12 pages, 11 figures; submitted to Phys. Rev.
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