75 research outputs found
Low-lying magnetic excitations of doubly-closed-shell nuclei and nucleon-nucleon effective interactions
We have studied the low lying magnetic spectra of 12C, 16O, 40Ca, 48Ca and
208Pb nuclei within the Random Phase Approximation (RPA) theory, finding that
the description of low-lying magnetic states of doubly-closed-shell nuclei
imposes severe constraints on the spin and tensor terms of the nucleon-nucleon
effective interaction. We have first made an investigation by using four
phenomenological effective interactions and we have obtained good agreement
with the experimental magnetic spectra, and, to a lesser extent, with the
electron scattering responses. Then we have made self-consistent RPA
calculations to test the validity of the finite-range D1 Gogny interaction. For
all the nuclei under study we have found that this interaction inverts the
energies of all the magnetic states forming isospin doublets.Comment: 19 pages, 13 figures, 7 tables, accepted for publication in Phys.
Rev.
Collective Excitations of (154)Sm nucleus at FEL{gamma}+LHC Collider
The production of collective excitations of the (154)Sm at FEL{gamma}+LHC
collider is investigated. We show that this machine will be a powerful tool for
investigation of high energy level excitations.Comment: 6 pages, 1 figure, 4 table
Photon data shed new light upon the GDR spreading width in heavy nuclei
A global study of the electric dipole strength in and below the isovector
giant dipole resonance (GDR) is presented for mass numbers A>80. It relies on
the recently established remarkably good match between data for the nuclear
photo effect to novel photon scattering data covering the region below the
neutron emission threshold as well as by average resonance neutron capture
(ARC). From the wide energy coverage of these data the correlation of the GDR
spreading width with energy can be studied with remarkable accuracy. A clear
sensitivity to details of the nuclear shape, i.e. the beta- and
gamma-deformations, is demonstrated. Based hereon a new parameterization of the
energy dependence of the nuclear electric-dipole strength is proposed which -
with only two new parameters - allows to describe the dipole strength in all
heavy nuclei with A>80. Although it differs significantly from previous
parameterizations it holds for spherical, transitional, triaxial and well
deformed nuclei. The GDR spreading width depends in a regular way on the
respective resonance energy, but it is independent of the photon energy.Comment: accepted by Phys. Lett. B after minor modification
Tensor effective interaction in self-consistent Random Phase Approximation calculations
We present a study of the effects of the tensor-isospin term of the effective
interaction in Hartree-Fock and Random Phase Approximation calculations. We
used finite-range forces of Gogny type, and we added to them a tensor-isospin
term which behaves, at large internucleonic distances, as the analogous term of
the microscopic interactions. The strength of this tensor force has been chosen
to reproduce the experimental energy of the lowest 0 excited state in
O, which shows large sensitivity to this term of the interaction. With
these finite-range interactions, we have studied the effects of the
tensor-isospin force in ground and excited states of carbon, oxygen, calcium,
nickel, zirconium, tin and lead isotopes. Our results show that the tensor
force affects mainly the nucleon single particle energies. However, we found
some interesting cases where also bulk nuclear properties are sensitive to the
tensor interaction.Comment: 18 pages, 14 figures, 3 table
Pygmy dipole strength close to particle-separation energies - the case of the Mo isotopes
The distribution of electromagnetic dipole strength in 92, 98, 100 Mo has
been investigated by photon scattering using bremsstrahlung from the new ELBE
facility. The experimental data for well separated nuclear resonances indicate
a transition from a regular to a chaotic behaviour above 4 MeV of excitation
energy. As the strength distributions follow a Porter-Thomas distribution much
of the dipole strength is found in weak and in unresolved resonances appearing
as fluctuating cross section. An analysis of this quasi-continuum - here
applied to nuclear resonance fluorescence in a novel way - delivers dipole
strength functions, which are combining smoothly to those obtained from
(g,n)-data. Enhancements at 6.5 MeV and at ~9 MeV are linked to the pygmy
dipole resonances postulated to occur in heavy nuclei.Comment: 6 pages, 5 figures, proceedings Nuclear Physics in Astrophysics II,
May 16-20, Debrecen, Hungary. The original publication is available at
www.eurphysj.or
Performance metrics and auditing framework using application kernels for high‐performance computer systems
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97468/1/cpe2871.pd
Photon scattering studies of the giant dipole resonance in medium weight nuclei
Quasimonochromatic photons have been used to measure elastic and inelastic photon scattering cross sections in the giant dipole resonance region of 52Cr, Fe, 60Ni, 92Mo, and 96Mo in an experiment in which the elastic and inelastic scattering are resolved. The elastic scattering cross sections show clear evidence for isospin splitting of the giant dipole resonance. The inelastic scattering to low-lying vibrational levels, which is a measure of the coupling between the giant dipole resonance and collective surface vibrations, is in qualitative agreement with the predictions of the dynamic collective model. However, when examined in detail, this model does not provide an adequate description of the scattering data
M1 Resonances in Unstable Magic Nuclei
Within a microscopic approach which takes into account RPA configurations,
the single-particle continuum and more complex
configurations isoscalar and isovector M1 excitations for the unstable nuclei
Ni and Sn are calculated. For comparison, the
experimentally known M1 excitations in Ca and Pb have also been
calculated. In the latter nuclei good agreement in the centroid energy, the
total transition strength and the resonance width is obtained. With the same
parameters we predict the magnetic excitations for the unstable nuclei. The
strength is sufficiently concentrated to be measurable in radioactive beam
experiments. New features are found for the very neutron rich nucleus Ni
and the neutron deficient nucleus Sn.Comment: 17 pages (LATEX), 12 figures (available from the authors),
KFA-IKP(TH)-1993-0
A Measurement of the Interference Structure Function, R_LT, for the 12C(e,e'p) reaction in the Quasielastic Region
The coincidence cross-section and the interference structure function, R_LT,
were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and
central momentum transfer of q=400 MeV/c. The measurement was at an opening
angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to
65 MeV. The R_LT structure function is found to be consistent with zero for E_m
> 50 MeV, confirming an earlier study which indicated that R_L vanishes in this
region. The integrated strengths of the p- and s-shell are compared with a
Distorted Wave Impulse Approximation calculation. The s-shell strength and
shape are compared with a Hartree Fock-Random Phase Approximation calculation.
The DWIA calculation overestimates the cross sections for p- and s-shell proton
knockout as expected, but surprisingly agrees with the extracted R_LT value for
both shells. The HF-RPA calculation describes the data more consistently, which
may be due to the inclusion of 2-body currents in this calculation.Comment: 8 Pages LaTex, 5 postscript figures. Submitted to Phys. Rev.
The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method
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