850 research outputs found
Microscopic Study of the Isoscalar Giant Monopole Resonance in Cd, Sn and Pb Isotopes
The isoscalar giant monopole resonance (ISGMR) in Cd, Sn and Pb isotopes has
been studied within the self-consistent Skyrme Hartree-Fock+BCS and
quasi-particle random phase approximation (QRPA). Three Skyrme parameter sets
are used in the calculations, i.e., SLy5, SkM* and SkP, since they are
characterized by different values of the compression modulus in symmetric
nuclear matter, namely K=230, 217, and 202 MeV, respectively. We also
investigate the effect of different types of pairing forces on the ISGMR in Cd,
Sn and Pb isotopes. The calculated peak energies and the strength distributions
of ISGMR are compared with available experimental data. We find that SkP fails
completely to describe the ISGMR strength distribution for all isotopes due to
its low value of the nuclear matter incompressibility, namely K=202 MeV. On the
other hand, the SLy5 parameter set, supplemented by an appropriate pairing
interaction, gives a reasonable description of the ISGMR in Cd and Pb isotopes.
A better description of ISGMR in Sn isotopes is achieved by the SkM*
interaction, that has a somewhat softer value of the nuclear incompressibility.Comment: Submitted to Phys. Rev.
Proton decay from the isoscalar giant dipole resonance in Ni
Proton decay from the 3 isoscalar giant dipole resonance (ISGDR)
in Ni has been measured using the () reaction at a
bombarding energy of 386 MeV to investigate its decay properties. We have
extracted the ISGDR strength under the coincidence condition between
inelastically scattered particles at forward angles and decay protons
emitted at backward angles. Branching ratios for proton decay to low-lying
states of Co have been determined, and the results compared to
predictions of recent continuum-RPA calculations. The final-state spectra of
protons decaying to the low-lying states in Co were analyzed for a more
detailed understanding of the structure of the ISGDR. It is found that there
are differences in the structure of the ISGDR as a function of excitation
energy.Comment: Minor changes after review. Accepted for publication in Phys. Rev. C.
19 pages; 7 figure
Effect of the tensor force on the charge-exchange spin-dipole excitations of 208Pb
The charge-exchange spin-dipole (SD) excitations of 208Pb are studied by
using a fully self-consistent Skyrme Hartree-Fock plus Random Phase
Approximation (HF+RPA) formalism which includes the tensor interaction. It is
found, for the first time, that the tensor correlations have a unique,
multipole-dependent effect on the SD excitations, that is, they produce
softening of 1- states, but hardening of 0- and 2- states. This paves the way
to a clear assessment of the strength of the tensor terms. We compare our
results with a recent measurement, showing that our choice of tensor terms
improves the agreement with experiment. The robustness of our results is
supported by the analytic form of the tensor matrix elements.Comment: 4 pages, 1 figure, 2 table
Self-consistent calculation of nuclear photoabsorption cross section: Finite amplitude method with Skyrme functionals in the three-dimensional real space
The finite amplitude method (FAM), which we have recently proposed (T.
Nakatsukasa, T. Inakura, and K. Yabana, Phys. Rev. C 76, 024318 (2007)),
simplifies significantly the fully self-consistent RPA calculation. Employing
the FAM, we are conducting systematic, fully self-consistent response
calculations for a wide mass region. This paper is intended to present a
computational scheme to be used in the systematic investigation and to show the
performance of the FAM for a realistic Skyrme energy functional. We implemented
the method in the mixed representation in which the forward and backward RPA
amplitudes are represented by indices of single-particle orbitals for occupied
states and the spatial grid points for unoccupied states. We solve the linear
response equation for a given frequency. The equation is a linear algebraic
problem with a sparse non-hermitian matrix, which is solved with an iterative
method. We show results of the dipole response for selected spherical and
deformed nuclei. The peak energies of the giant dipole resonance agree well
with measurements for heavy nuclei, while they are systematically
underestimated for light nuclei. We also discuss the width of the giant dipole
resonance in the fully self-consistent RPA calculation.Comment: 11 pages, 10 figure
Isotopic dependence of the giant monopole resonance in the even-A ^{112-124}Sn isotopes and the asymmetry term in nuclear incompressibility
The strength distributions of the giant monopole resonance (GMR) have been
measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of
400-MeV particles in the angular range
--. We find that the experimentally-observed GMR energies
of the Sn isotopes are lower than the values predicted by theoretical
calculations that reproduce the GMR energies in Pb and Zr very
well. From the GMR data, a value of MeV is obtained
for the asymmetry-term in the nuclear incompressibility.Comment: Submitted to Physical Review Letters. 10 pages; 4 figure
Isoscalar dipole strength in ^{208}_{82}Pb_{126}: the spurious mode and the strength in the continuum
Isoscalar dipole (compression) mode is studied first using schematic
harmonic-oscillator model and, then, the self-consistent Hartree-Fock (HF) and
random phase approximation (RPA) solved in coordinate space. Taking ^{208}Pb
and the SkM* interaction as a numerical example, the spurious component and the
strength in the continuum are carefully examined using the sum rules. It is
pointed out that in the continuum calculation one has to use an extremely fine
radial mesh in HF and RPA in order to separate, with good accuracy, the
spurious component from intrinsic excitations.Comment: 19 pages, 2 figure
Breathing mode in an improved transport approach
The nuclear breathing-mode giant monopole resonance is studied within an
improved relativistic Boltzmann-Uehling-Uhlenbeck (BUU) transport approach. As
a new feature, the numerical treatment of ground state nuclei and their
phase-space evolution is realized with the same semiclassical energy density
functional. With this new method a very good stability of ground state nuclei
in BUU simulations is achieved. This is important in extracting clear
breathing-mode signals for the excitation energy and, in particular, for the
lifetime from transport theoretical studies including mean-field and
collisional effects.Comment: 33 pages, 11 figures, accepted for publication in Phys. Rev.
Isospin properties of electric dipole excitations in 48Ca
Two different experimental approaches were combined to study the electric
dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold.
Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and
nearly mono-energetic linearly polarized photons with energies between 6.6 and
9.51 MeV provided strength distribution and parities, and an
(\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for
an isoscalar probe. The unexpected difference observed in the dipole response
is compared to calculations using the first-order random-phase approximation
and points to an energy-dependent isospin character. A strong isoscalar state
at 7.6 MeV was identified for the first time supporting a recent theoretical
prediction.Comment: 6 pages, 5 figures, as accepted in Phys. Lett.
Overtones of Isoscalar Giant Resonances in medium-heavy and heavy nuclei
A semi-microscopic approach based on both the
continum-random-phase-approximation (CRPA) method and a phenomenological
treatment of the spreading effect is extended and applied to describe the main
properties (particle-hole strength distribution, energy-dependent transition
density, partial direct-nucleon-decay branching ratios) of the isoscalar giant
dipole, second monopole, and second quadrupole resonances. Abilities of the
approach are checked by description of gross properties of the main-tone
resonances. Calculation results obtained for the resonances in a few singly-
and doubly-closed-shell nuclei are compared with available experimental data.Comment: 12 pages, 14 figures, submitted to Phys. Rev.
Time scales in nuclear giant resonances
We propose a general approach to characterise fluctuations of measured cross
sections of nuclear giant resonances. Simulated cross sections are obtained
from a particular, yet representative self-energy which contains all
information about fragmentations. Using a wavelet analysis, we demonstrate the
extraction of time scales of cascading decays into configurations of different
complexity of the resonance. We argue that the spreading widths of collective
excitations in nuclei are determined by the number of fragmentations as seen in
the power spectrum. An analytic treatment of the wavelet analysis using a
Fourier expansion of the cross section confirms this principle. A simple rule
for the relative life times of states associated with hierarchies of different
complexity is given.Comment: 5 pages, 4 figure
- …