121 research outputs found
A nucleonic NJL model for finite nuclei: dynamic mass generation and ground-state observables
We test the compatibility of chiral symmetry, dynamic mass generation of the
nucleon due to spontaneous breaking of chiral symmetry, and the description of
finite nuclear systems by employing an NJL model understood as a chiral
invariant effective theory for nucleons. We apply the model to nuclear matter
as well as to finite nuclei. In the latter case, the model is adjusted to
nuclear ground-state observables. We treat the case of a pure chiral theory and
the physically more realistic case where a portion of the nucleon mass (160
MeV) explicitly breaks chiral symmetry. The best version of this current model
is found to deliver reasonably good results simultaneously for both finite
nuclei and the nucleon mass, which supports our motivation of probing a link
between low-momentum QCD and the nuclear many-body problem. However, the
observables calculated for finite nuclei are not as good as those coming from
existing relativistic mean field models without explicit chiral symmetry.Comment: 19 pages, 3 eps figures, accepted for publication in Nucl. Phys.
Recent progress in the study of fission barriers in covariant density functional theory
Recent progress in the study of fission barriers of actinides and superheavy
nuclei within covariant density functional theory is overviewed.Comment: 10 pages, 5 figures. In press in International Journal of Modern
Physics
Final excitation energy of fission fragments
We study how the excitation energy of the fully accelerated fission fragments
is built up. It is stressed that only the intrinsic excitation energy available
before scission can be exchanged between the fission fragments to achieve
thermal equilibrium. This is in contradiction with most models used to
calculate prompt neutron emission where it is assumed that the total excitation
energy of the final fragments is shared between the fragments by the condition
of equal temperatures. We also study the intrinsic excitation-energy partition
according to a level density description with a transition from a
constant-temperature regime to a Fermi-gas regime. Complete or partial
excitation-energy sorting is found at energies well above the transition
energy.Comment: 8 pages, 3 figure
Event-by-event study of neutron observables in spontaneous and thermal fission
The event-by-event fission model FREYA is extended to spontaneous fission of
actinides and a variety of neutron observables are studied for spontaneous
fission and fission induced by thermal neutrons with a view towards possible
applications for detection of special nuclear materials.Comment: 16 pages, 24 figure
Exploring continuum structures with a pseudo-state basis
The ability of a recently developed square-integrable discrete basis to
represent the properties of the continuum of a two-body system is investigated.
The basis is obtained performing a simple analytic local scale transformation
to the harmonic oscillator basis. Scattering phase-shifts and the electric
transition probabilities B(E1) and B(E2) have been evaluated for several
potentials using the proposed basis. Both quantities are found to be in
excellent agreement with the exact values calculated from the true scattering
states. The basis has been applied to describe the projectile continuum in the
6He scattering by 12C and 208Pb targets at 240 MeV/nucleon and the 11Be
scattering by 12C at 67 MeV/nucleon. The calculated breakup differential cross
sections are found to be in very good agreement with the available experimental
data for these reactions.Comment: 17 pages, 10 figures (Version to appear in Phys. Rev. C
Predicting total reaction cross sections for nucleon-nucleus scattering
Nucleon total reaction and neutron total cross sections to 300 MeV for 12C
and 208Pb, and for 65 MeV spanning the mass range, are predicted using
coordinate space optical potentials formed by full folding of effective
nucleon-nucleon interactions with realistic nuclear ground state densities.
Good to excellent agreement is found with existing data.Comment: 10 pages, 4 figure
Description of nuclear systems within the relativistic Hartree-Fock method with zero range self-interactions of the scalar field
An exact method is suggested to treat the nonlinear self-interactions (NLSI)
in the relativistic Hartree-Fock (RHF) approach for nuclear systems. We
consider here the NLSI constructed from the relativistic scalar nucleon
densities and including products of six and eight fermion fields. This type of
NLSI corresponds to the zero range limit of the standard cubic and quartic
self-interactions of the scalar field. The method to treat the NLSI uses the
Fierz transformation, which enables one to express the exchange (Fock)
components in terms of the direct (Hartree) ones. The method is applied to
nuclear matter and finite nuclei. It is shown that, in the RHF formalism, the
NLSI, which are explicitly isovector-independent, generate scalar, vector and
tensor nucleon self-energies strongly density-dependent. This strong isovector
structure of the self-energies is due to the exchange terms of the RHF method.
Calculations are carried out with a parametrization containing five free
parameters. The model allows a description of both types of systems compatible
with experimental data.Comment: 23 pages, 14 figures (v2: major quantitative changes
A large Hilbert space QRPA and RQRPA calculation of neutrinoless double beta decay
A large Hilbert space is used for the calculation of the nuclear matrix
elements governing the light neutrino mass mediated mode of neutrinoless double
beta decay of Ge76, Mo100, Cd116, Te128 and Xe136 within the proton-neutron
quasiparticle random phase approximation (pn-QRPA) and the renormalized QRPA
with proton-neutron pairing (full-RQRPA) methods. We have found that the
nuclear matrix elements obtained with the standard pn-QRPA for several nuclear
transitions are extremely sensitive to the renormalization of the
particle-particle component of the residual interaction of the nuclear
hamiltonian. Therefore the standard pn-QRPA does not guarantee the necessary
accuracy to allow us to extract a reliable limit on the effective neutrino
mass. This behaviour, already known from the calculation of the two-neutrino
double beta decay matrix elements, manifests itself in the neutrinoless
double-beta decay but only if a large model space is used. The full-RQRPA,
which takes into account proton-neutron pairing and considers the Pauli
principle in an approximate way, offers a stable solution in the physically
acceptable region of the particle-particle strength. In this way more accurate
values on the effective neutrino mass have been deduced from the experimental
lower limits of the half-lifes of neutrinoless double beta decay.Comment: 19 pages, RevTex, 1 Postscript figur
Isospin Dependence in the Odd-Even Staggering of Nuclear Binding Energies
The FRS-ESR facility at GSI provides unique conditions for precision
measurements of large areas on the nuclear mass surface in a single experiment.
Values for masses of 604 neutron-deficient nuclides (30<=Z<=92) were obtained
with a typical uncertainty of 30 microunits. The masses of 114 nuclides were
determined for the first time. The odd-even staggering (OES) of nuclear masses
was systematically investigated for isotopic chains between the proton shell
closures at Z=50 and Z=82. The results were compared with predictions of modern
nuclear models. The comparison revealed that the measured trend of OES is not
reproduced by the theories fitted to masses only. The spectral pairing gaps
extracted from models adjusted to both masses, and density related observables
of nuclei agree better with the experimental data.Comment: Physics Review Letters 95 (2005) 042501
http://link.aps.org/abstract/PRL/v95/e04250
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