438 research outputs found
Low-energy magnetic radiation: deviations from GOE
A pronounced spike at low energy in the strength function for magnetic
radiation (LEMAR) is found by means of Shell Model calculations, which explains
the experimentally observed enhancement of the dipole strength. LEMAR
originates from statistical low-energy M1-transitions between many excited
complex states. Re-coupling of the proton and neutron high-j orbitals generates
the strong magnetic radiation. LEMAR is closely related to Magnetic Rotation.
LEMAR is predicted for nuclides participating in the r-process of element
synthesis and is expected to change the reaction rates. An exponential decrease
of the strength function and a power law for the size distribution of the
values are found, which strongly deviate from the ones of the GOE of
random matrices, which is commonly used to represent complex compound states.Comment: Proceedings of the conference on Nuclei and Mesoscopic Physics 2014,
MSU, to be published AIP Conference Proceeding
Low-energy enhancement of magnetic dipole radiation
Magnetic dipole strength functions have been deduced from averages of a large
number of transition strengths calculated within the shell model for the
nuclides Zr, Mo, Mo, and Mo. An enhancement of
strength toward low transition energy has been found for all nuclides
considered. Large strengths appear for transitions between close-lying
states with configurations including proton as well as neutron high- orbits
that re-couple their spins and add up their magnetic moments coherently. The
strength function deduced from the calculated transition strengths is
compatible with the low-energy enhancement found in (He,He') and
experiments. The present work presents for the first time an
explanation of the experimental findings
Spectroscopic features of low-energy excitations in skin nuclei
Systematic studies of dipole and other multipole excitations in stable and
exotic nuclei are discussed theoretically. Exploring the relation of the
strengths of low-energy dipole and quadrupole pygmy resonances to the thickness
of the neutron (proton) skin a close connection between static and dynamic
properties of the nucleus is observed. The fine structure of low-energy dipole
strength in 138Ba nucleus is revealed from E1 and spin-flip M1 strengths
distributions.Comment: A Talk given at the Int. Symposium 'Forefronts of Researches in
Exotic Nuclear Structures - Niigata2010 -', 1-4 March, 2010, Tokamachi,
Niigata, Japan; to be published in a volume of Modern Physics Letters A
(MPLA)
Photodissociation of p-process nuclei studied by bremsstrahlung induced activation
A research program has been started to study experimentally the
near-threshold photodissociation of nuclides in the chain of cosmic heavy
element production with bremsstrahlung from the ELBE accelerator. An important
prerequisite for such studies is good knowledge of the bremsstrahlung
distribution which was determined by measuring the photodissociation of the
deuteron and by comparison with model calculations. First data were obtained
for the astrophysically important target nucleus 92-Mo by observing the
radioactive decay of the nuclides produced by bremsstrahlung irradiation at
end-point energies between 11.8 MeV and 14.0 MeV. The results are compared to
recent statistical model calculations.Comment: 6 pages, 8 figures, Proceedings Nuclear Physics in Astrophysics II,
May 16-20, 2005, Debrecen, Hungary. The original publication is available at
www.eurphysj.or
Photon strength distributions in stable even-even molybdenum isotopes
Electromagnetic dipole-strength distributions up to the particle separation
energies are studied for the stable even-even nuclides Mo
in photon scattering experiments at the superconducting electron accelerator
ELBE of the Forschungszentrum Dresden-Rossendorf. The influence of inelastic
transitions to low-lying excited states has been corrected by a simulation of
cascades using a statistical model. After corrections for branching
ratios of ground-state transitions, the photon-scattering cross-sections
smoothly connect to data obtained from -reactions. With the newly
determined electromagnetic dipole response of nuclei well below the particle
separation energies the parametrisation of the isovector giant-dipole resonance
is done with improved precision.Comment: Proceedings Nuclear Physics in Astrophysics 3, March 2007, Dresden
Journal of Physics G, IOP Publishin
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