996 research outputs found
Large-angle scattering and quasi-elastic barrier distributions
We study in detail the barrier distributions extracted from large-angle
quasi-elastic scattering of heavy ions at energies near the Coulomb barrier.
Using a closed-form expression for scattering from a single barrier, we compare
the quasi-elastic barrier distribution with the corresponding test function for
fusion. We examine the isocentrifugal approximation in coupled-channels
calculations of quasi-elastic scattering and find that for backward angles, it
works well, justifying the concept of a barrier distribution for scattering
processes. This method offers an interesting tool for investigating unstable
nuclei. We illustrate this for the Mg + Pb reaction, where the
quadrupole collectivity of the neutron-rich Mg remains to be clarified
experimentally.Comment: 26 pages, 10 eps figure
Role of non-collective excitations in heavy-ion fusion reactions and quasi-elastic scattering around the Coulomb barrier
Despite the supposed simplicity of double-closed shell nuclei, conventional
coupled-channels calculations, that include all of the known collective states
of the target and projectile, give a poor fit to the fusion cross section for
the O + Pb system. The discrepancies are highlighted through the
experimental barrier distribution and logarithmic derivative, that are both
well defined by the precise experimental fusion data available. In order to
broaden our search for possible causes for this anomaly, we revisit this system
and include in our calculations a large number of non-collective states of the
target, whose spin, parity, excitation energy and deformation paramter are
known from high-precision proton inelastic-scattering measurements. Although
the new coupled-channels calculations modify the barrier distribution, the
disagreemnt with experiment remains both for fusion and for quasi-elastic (QE)
scattering. We find that the Q-value distributions for large-angle QE
scattering become rapidly more important as the incident energy increases,
reflecting the trend of the experimental data. The mass-number dependence of
the non-collective excitations is discussed.Comment: 8 pages, 7 figure
Iterative solution of a Dirac equation with inverse Hamiltonian method
We solve a singe-particle Dirac equation with Woods-Saxon potentials using an
iterative method in the coordinate space representation. By maximizing the
expectation value of the inverse of the Dirac Hamiltonian, this method avoids
the variational collapse, in which an iterative solution dives into the Dirac
sea. We demonstrate that this method works efficiently, reproducing the exact
solutions of the Dirac equation.Comment: 4 pages, 3 figure
Hierarchical Equations of Motion Approach to Quantum Thermodynamics
We present a theoretical framework to investigate quantum thermodynamic
processes under non-Markovian system-bath interactions on the basis of the
hierarchical equations of motion (HEOM) approach, which is convenient to carry
out numerically "exact" calculations. This formalism is valuable because it can
be used to treat not only strong system-bath coupling but also system-bath
correlation or entanglement, which will be essential to characterize the heat
transport between the system and quantum heat baths. Using this formalism, we
demonstrated an importance of the thermodynamic effect from the tri-partite
correlations (TPC) for a two-level heat transfer model and a three-level
autonomous heat engine model under the conditions that the conventional quantum
master equation approaches are failed. Our numerical calculations show that TPC
contributions, which distinguish the heat current from the energy current, have
to be take into account to satisfy the thermodynamic laws.Comment: 9 pages, 4 figures. As a chapter of: F. Binder, L. A. Correa, C.
Gogolin, J. Anders, and G. Adesso (eds.), "Thermodynamics in the quantum
regime - Recent Progress and Outlook", (Springer International Publishing
Time-Dependent Generator Coordinate Method for Many-Particle Tunneling
It has been known that the time-dependent Hartree-Fock (TDHF) method, or the
time-dependent density functional theory (TDDFT), fails to describe many-body
quantum tunneling. We overcome this problem by superposing a few time-dependent
Slater determinants with the time-dependent generator coordinate method
(TDGCM). We apply this method to scattering of two particles in one
dimension, and demonstrate that the TDGCM method yields a finite tunneling
probability even at energies below the Coulomb barrier, at which the tunneling
probability is exactly zero in the TDHF. This is the first case in which a
many-particle tunneling is simulated with a microscopic real-time approach.Comment: 9 pages, 4 figure
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