988 research outputs found
Effect of pairing on one- and two-nucleon transfer below the Coulomb barrier: a time-dependent microscopic description
The effect of pairing correlation on transfer reaction below the Coulomb
barrier is investigated qualitatively and quantitatively using a simplified
version of the Time-Dependent Hartree-Fock + BCS approach. The effect of
particle number symmetry breaking on the description of reaction and dedicated
methods to extract one and two-nucleon transfer probabilities (P_{1n} and
P_{2n}) in a particle number symmetry breaking approach are discussed.
Influence of pairing is systematically investigated in the ^{40}Ca+
^{40,42,44,46,48,50}Ca reactions. A strong enhancement of the two-particle
transfer probabilities due to initial pairing correlations is observed. This
enhancement induces an increase of the ratio of probabilities P_{2n} /
(P_{1n})^2 compared to the case with no pairing. It is shown that this ratio
increases strongly as the center of mass energy decreases with a value that
could be larger than ten in the deep sub-barrier regime. An analysis of the
pair transfer sensitivity to the type of pairing interaction, namely surface,
mixed or volume, used in the theory is made. It is found that the pair transfer
is globally insensitive to the type of force and mainly depends on the pairing
interaction strength.Comment: 12 pages, 10 figure
Systematic of isovector and isoscalar giant quadrupole resonances in normal and superfluid spherical nuclei
The isoscalar (IS) and isovector (IV) quadrupole responses of nuclei are
systematically investigated using the time-dependent Skyrme Energy Density
Functional including pairing in the BCS approximation. Using two different
Skyrme functionals, Sly4 and SkM*, respectively 263 and 304 nuclei have been
found to be spherical along the nuclear charts. The time-dependent evolution of
these nuclei has been systematically performed giving access to their
quadrupole responses. It is shown that the mean-energy of the collective high
energy state globally reproduces the experimental IS and IV collective energy
but fails to reproduce their lifetimes. It is found that the mean collective
energy depends rather significantly on the functional used in the mean-field
channel. Pairing by competing with parity effects can slightly affect the
collective response around magic numbers and induces a reduction of the
collective energy compared to the average trend. Low-lying states, that can
only be considered if pairing is included, are investigated. While the approach
provides a fair estimate of the low lying state energy, it strongly
underestimates the transition rate . Finally, the possibility to access
to the density dependence of the symmetry energy through parallel measurements
of both the IS- and IV-GQR is discussed.Comment: 14 pages, 19 figure
Systematic of isovector and isoscalar giant quadrupole resonances in normal and superfluid deformed nuclei
The systematic study of isoscalar (IS) and isovector (IV) giant quadrupole
responses (GQR) in normal and superfluid nuclei presented in [G. Scamps and D.
Lacroix, Phys. Rev. 88, 044310 (2013)] is extended to the case of axially
deformed and triaxial nuclei. The static and dynamical energy density
functional based on Skyrme effective interaction are used to study static
properties and dynamical response functions over the whole nuclear chart. Among
the 749 nuclei that are considered, 301 and 65 are respectively found to be
prolate and oblate while 54 do not present any symmetry axis. For these nuclei,
the IS- and IV-GQR response functions are systematically obtained. In these
nuclei, different aspects related to the interplay between deformation and
collective motion are studied. We show that some aspects like the fragmentation
of the response induced by deformation effects in axially symmetric and
triaxial nuclei can be rather well understood using simple arguments. Besides
this simplicity, more complex effects show up like the appearance of
non-trivial deformation effects on the collective motion damping or the
influence of hexadecapole or higher-orders effects. A specific study is made on
the triaxial nuclei where the absence of symmetry axis adds further complexity
to the nuclear response. The relative importance of geometric deformation
effects and coupling to other vibrational modes are discussed.Comment: 17 pages, 26 figure
Beyond mean-field calculation for pairing correlation
The recently proposed Symmetry-Conserving Energy Density Functional approach
[G. Hupin, D. Lacroix and M. Bender, Phys. Rev. C84, 014309 (2011)] is applied
to perform Variation After Projection onto good particle number using Skyrme
interaction, including density dependent terms. We present a systematic study
of the Kr and Sn isotopic chains. This approach leads to non-zero pairing in
magic nuclei and a global enhancement of the pairing gap compared to the
original theory that breaks the particle number symmetry. The need to
consistently readjust the pairing effective interaction strength is discussed.Comment: 7 pages, 9 figure
Density functional for pairing with particle number conservation
In this work, a new functional is introduced to treat pairing correlations in
finite many-body systems. Guided by the projected BCS framework, the energy is
written as a functional of occupation numbers. It is shown to generalize the
BCS approach and to provide an alternative to Variation After Projection
framework. Illustrations of the new approach are given for the pairing
Hamiltonian for various particle numbers and coupling strengths. In all case, a
very good agreement with the exact solution is found.Comment: Proceeding of the International Symposium: Forefronts of Researches
in Exotic Nuclear Structures- Niigata201
Collectivity in small and large amplitude microscopic mean-field dynamic
The time-dependent energy density functional with pairing allows to describe
a large variety of phenomena from small to large amplitude collective motion.
Here, we briefly summarize the recent progresses made in the field using the
TD-BCS approach. A focus is made on the mapping of the microscopic mean-field
dynamic to the macroscopic dynamic in collective space. A method is developed
to extract the collective mass parameter from TD-EDF. Illustration is made on
the fission of Fm. The collective mass and collective momentum
associated to quadrupole deformation including non-adiabatic effects is
estimated along the TD-EDF path. With these information, the onset of
dissipation during fission is discussed.Comment: Proceeding of the XXII Nuclear Physics Workshop, Kazimierz, 2015,
Polan
On the formulation of functional theory for pairing with particle number restoration
The restoration of particle number within Energy Density Functional theory is
analyzed. It is shown that the standard method based on configuration mixing
leads to a functional of both the projected and non-projected densities. As an
alternative that might be advantageous for mass models, nuclear dynamics and
thermodynamics, we propose to formulate the functional in terms directly of the
one-body and two-body density matrices of the state with good particle number.
Our approach does not contain the pathologies recently observed when restoring
the particle number in an Energy Density Functional framework based on
transition density matrices and can eventually be applied with functionals
having arbitrary density dependencies.Comment: 11 pages, 3 figure
Dynamical description of the fission process using the TD-BCS theory
The description of fission remains a challenge for nuclear microscopic
theories. The time-dependent Hartree-Fock approach with BCS pairing is applied
to study the last stage of the fission process. A good agreement is found for
the one-body observables: the total kinetic energy and the average mass
asymmetry. The non-physical dependence of two-body observables with the initial
shape is discussed.Comment: 4 pages, 3 figures, Submitted as AIP Conference Proceeings for
NSD2015, Portoroz, Sloveni
Collective aspects deduced from time-dependent microscopic mean-field with pairing: application to the fission process
Given a set of collective variables, a method is proposed to obtain the
associated conjugated collective momenta and masses starting from a microscopic
time-dependent mean-field theory. The construction of pairs of conjugated
variables is the first step to bridge microscopic and macroscopic approaches.
The method is versatile and can be applied to study a large class of nuclear
processes. An illustration is given here with the fission of Fm. Using
the quadrupole moment and eventually higher-order multipole moments, the
associated collective masses are estimated along the microscopic mean-field
evolution. When more than one collective variable are considered, it is shown
that the off-diagonal matrix elements of the inertia play a crucial role. Using
the information on the quadrupole moment and associated momentum, the
collective evolution is studied. It is shown that dynamical effects beyond the
adiabatic limit are important. Nuclei formed after fission tend to stick
together for longer time leading to a dynamical scission point at larger
distance between nuclei compared to the one anticipated from the adiabatic
energy landscape. The effective nucleus-nucleus potential felt by the emitted
nuclei is finally extracted.Comment: 12 pages, 9 figure
Microscopic description of large amplitude collective motion in the nuclear astrophysics context
In the last 10 years, we have observed an important increase of interest in
the application of time-dependent energy density functional theory (TD-EDF).
This approach allows to treat nuclear structure and nuclear reaction from small
to large amplitude dynamics in a unified framework. The possibility to perform
unrestricted three-dimensional simulations using state of the art effective
interactions has opened new perspectives. In the present article, an overview
of applications where the predictive power of TD-EDF has been benchmarked is
given. A special emphasize is made on processes that are of astrophysical
interest. Illustrations discussed here include giant resonances, fission,
binary and ternary collisions leading to fusion, transfer and deep inelastic
processes.Comment: To appear in a special issue of IJMPE on "Collectivity in Nuclei,
Neutrinos, and Neutron Stars
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