Guillaume Scamps

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.

Systematic study of isovector and isoscalar giant quadrupole resonances in normal and superfluid deformed 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 B(E2). Finally, the possibility to access to the density dependence of the symmetry energy through parallel measurements of both the ISand IV-GQR is discussed.

Pairing dynamics in particle transport

We analyze the effect of pairing on particle transport in time-dependent theories based on the Hartree-FockBogoliubov (HFB) or BCS approximations. The equations of motion for the HFB density matrices are unique and the theory respects the usual conservation laws defined by commutators of the conserved quantity with the Hamiltonian. In contrast, the theories based on the BCS approximation are more problematic. In the usual formulation of time-dependent Hartree-Fock (TDHF) + BCS, the equation of continuity is violated and one sees unphysical oscillations in particle densities. This can be ameliorated by freezing the occupation numbers during theevolutioninTDHF + BCS,butthereareotherproblemswiththeBCSapproximationthatmakeitdoubtfulfor reaction dynamics. We also compare different numerical implementations of the time-dependent HFB equations. The equations of motion for the U and V Bogoliubov transformations are not unique, but it appears that the usual formulation is also the most efficient. Finally, we compare the time-dependent HFB solutions with numerically

Neutron-pair transfer in the sub-barrier capture process

The sub-barrier capture reactions following the neutron pair transfer are proposed to be used for the indirect study of neutron-neutron correlation in the surface region of nucleus. The strong effect of the dineutron-like clusters transfer stemming from the surface of magic and non-magic nuclei

Collective aspects deduced from time-dependent microscopic mean-field with pairing: Application to the fission process

^{18}

Transfer probabilities for the reactions O14,20+O20 in terms of multiple time-dependent Hartree-Fock-Bogoliubov trajectories

O,

Gauge angle dependence in time-dependent Hartree-Fock-Bogoliubov calculations of O 20 + O 20 head-on collisions with the Gogny interaction

^{48}

Polarization of the nuclear surface in deformed nuclei

Ca,

Coupled-channels description of multinucleon transfer and fusion reactions at energies near and far below the Coulomb barrier

^{64}

Microscopic description of large amplitude collective motion in the nuclear astrophysics context

Ni,