87 research outputs found
Compilation of Giant Electric Dipole Resonances Built on Excited States
Giant Electric Dipole Resonance (GDR) parameters for gamma decay to excited
states with finite spin and temperature are compiled. Over 100 original works
have been reviewed and from some 70 of which more than 300 parameter sets of
hot GDR parameters for different isotopes, excitation energies, and spin
regions have been extracted. All parameter sets have been brought onto a common
footing by calculating the equivalent Lorentzian parameters. The current
compilation is complementary to an earlier compilation by Samuel S. Dietrich
and Barry L. Berman (At. Data Nucl. Data Tables 38(1988)199-338) on
ground-state photo-neutron and photo-absorption cross sections and their
Lorentzian parameters. A comparison of the two may help shed light on the
evolution of GDR parameters with temperature and spin. The present compilation
is current as of January 2006.Comment: 31 pages including 1 tabl
Evidence for the Jacobi shape transition in hot 46Ti
The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in
the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an
experiment using a setup consisting of the combined EUROBALL IV, HECTOR and
EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the
predictions of the thermal shape fluctuation model shows evidence for the
Jacobi shape transition in hot 46Ti. In addition to the previously found broad
structure in the GDR lineshape region at 18-27 MeV caused by large
deformations, the presence of a low energy component (around 10 MeV), due to
the Coriolis splitting in prolate well deformed shape, has been identified for
the first time.Comment: 8 pages, 4 figures, proceedings of the COMEX1 conference, June 2003,
Paris; to be published in Nucl. Phys.
Critical behavior in the variation of GDR width at low temperature
We present the first experimental giant dipole resonance (GDR) width
systematics, in the temperature region 0.8 1.2 MeV for Tl, a
near Pb nucleus, to investigate the evolution of the GDR width in shell effect
& pairing dominated region. The extracted GDR widths are well below the
predictions of shell effect corrected thermal shape fluctuation model (TSFM)
and thermal pairing included phonon damping model. A similar behavior of the
GDR width is also observed for Cu measured in the present work and
Sb, measured earlier. This discrepancy is attributed to the GDR induced
quadrupole moment leading to a critical point in the increase of the GDR width
with temperature. We incorporate this novel idea in the phenomenological
description based on the TSFM for a better understanding of the GDR width
systematics for the entire range of mass, spin and temperature.Comment: Accepted for publication in Phys. Lett. B, 7 pages, 4 figure
Scaling Properties of the Giant Dipole Resonance Width in Hot Rotating nuclei
We study the systematics of the giant dipole resonance width in hot
rotating nuclei as a function of temperature , spin and mass . We
compare available experimental results with theoretical calculations that
include thermal shape fluctuations in nuclei ranging from A=45 to A=208. Using
the appropriate scaled variables, we find a simple phenomenological function
which approximates the global behavior of the giant dipole
resonance width in the liquid drop model. We reanalyze recent experimental and
theoretical results for the resonance width in Sn isotopes and Pb.Comment: LaTeX, 4 pages with 4 figures (to appear in Phys. Rev. Lett.
The damping width of giant dipole resonances of cold and hot nuclei: a macroscopic model
A phenomenological macroscopic model of the Giant Dipole Resonance (GDR)
damping width of cold- and hot-nuclei with ground-state spherical and
near-spherical shapes is developed. The model is based on a generalized Fermi
Liquid model which takes into account the nuclear surface dynamics. The
temperature dependence of the GDR damping width is accounted for in terms of
surface- and volume-components. Parameter-free expressions for the damping
width and the effective deformation are obtained. The model is validated with
GDR measurements of the following nuclides, K, Ca, Sc,
Cu, Sn,Eu, Hg, and Pb, and is
compared with the predictions of other models.Comment: 10 pages, 5 figure
Reaction mechanisms in the 6Li+59Co system
The reactions induced by the weakly bound 6Li projectile interacting with the
intermediate mass target 59Co were investigated. Light charged particles
singles and - coincidence measurements were performed at the near
barrier energies E_lab = 17.4, 21.5, 25.5 and 29.6 MeV. The main contributions
of the different competing mechanisms are discussed. A statistical model
analysis, Continuum-Discretized Coupled-Channels calculations and two-body
kinematics were used as tools to provide information to disentangle the main
components of these mechanisms. A significant contribution of the direct
breakup was observed through the difference between the experimental sequential
breakup cross section and the CDCC prediction for the non-capture breakup cross
section.Comment: 30 pages, 8 figure
Deformation Effects in Hot Rotating 46Ti Probed by the Charged Particle Emission and GDR gamma-Decay
The 46Ti* compound nucleus, as populated by the fusion-evaporation reaction
27Al+19F at the bombarding energy of E_lab=144 MeV, has been investigated by
charged particle spectroscopy using the multidetector array ICARE at the
VIVITRON tandem facility of the IReS (Strasbourg). The light charged particles
and high-energy gamma-rays from the GDR decay have been measured in coincidence
with selected evaporation residues. The CACARIZO code, a Monte Carlo
implementation of the statistical-model code CASCADE, has been used to
calculate the spectral shapes of evaporated alpha-particles which are compared
with the experimental coincident spectra. This comparison indicates the
signature of large deformations (possibly superdeformed and hyperdeformed
shapes) present in the compound nucleus decay. The occurrence of the Jacobi
shape transition is also discussed in the framework of a newly developed
rotating liquid drop model.Comment: contribution to the COMEX2 conference proceedings, to be published in
Nucl. Phys.
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High Energy Gamma Rays from p+X, X=Cu, Ag, Au at 34 MeV
In this paper we present results from the measurement of the gamma ray yield in the reaction of 34-MeV protons on Cu, Ag and Au. The protons were produced by the University of Washington superconducting linac. The gamma rays were measured using a large NaI and two large BaF{sub 2} detectors. Angular distributions were obtained for each of the three targets. Data for the Cu and Ag target were taken at six lab angles between 35 and 135 degrees, while data were taken at eight lab angles between 35 and 135 degrees for the Au target. The data were compared to several models. These included Hauser-Feshbach and direct-semidirect (DSD) calculations. We also compared the measurements to proton-nucleus bremsstrahlung calculations. The bremsstrahlung calculations greatly underpredicted the cross section and produced an angular distribution which was too flat. The Hauser-Feshbach calculations reproduced the yield of the softer portion of the spectrum reasonably well for all three targets. The DSD calculations reproduced the yield and angular distributions quite well for energies above about 20 MeV. However, the yields were underpredicted in the 15-18 MeV region, which suggests that multistep mechanisms may be needed for this target
Testing ab initio nuclear structure in neutron-rich nuclei: Lifetime measurements of second 2+ state in 16C and 20O
To test the predictive power of ab initio nuclear structure theory, the lifetime of the second 2+ state in neutron-rich 20O,τ(2+2)=150+80−30fs, and an estimate for the lifetime of the second 2+ state in 16C have been obtained for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds of femtoseconds range by analyzing the Doppler-shifted γ-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction 18O(7.0MeV/u)+181Ta. The requested sensitivity could only be reached owing to the excellent performances of the Advanced γ-Tracking Array AGATA, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two- and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for 20O and with the no-core shell model for 16C. The present measurement shows the power of electromagnetic observables, determined with high-precision γ spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetime measurements in unexplored regions of the nuclear chart, including r-process nuclei, when intense beams, produced by Isotope Separation On-Line (ISOL) techniques, become available
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