36 research outputs found
Density matrix renormalization group description of the island of inversion isotopes F
Recent experiments have confirmed that the neutron-rich isotopes F
belong to the so-called island of inversion (IOI), a region of the nuclear
chart around and where nuclear structure deviates from the
standard shell model predictions due to deformation and continuum effects.
However, while the general principles leading to the IOI are relatively well
understood, the details of the low-lying structure of the exotic fluorine
isotopes F are basically unknown. In this work, we perform
large-scale shell model calculations including continuum states to investigate
the properties of the neutron-rich isotopes F, using a core of
O and an effective two-body interaction with only three adjustable
parameters. We adjust the core potential and interaction on experimentally
confirmed states in O and F and solve the many-body problem
using the density matrix renormalization group method for open quantum systems
in a - model space. We obtain the first detailed spectroscopy of
F in the continuum and show how the interplay between continuum
effects and deformation explains the recent data on F, and produces
an inversion of the and states in F. Several
deformed one- and two-neutron halo states are predicted in F, and we
predict the ground state of F to have a structure similar to that of the
first state of F. We also suggest several experimental studies
to constraint models and test the present predictions. The complex structure of
neutron-rich fluorine isotopes offers a trove of information about the
formation of the southern shore of the IOI through a subtle interplay of
deformation and continuum couplings driven by the occupation of the
quasi-degenerate neutron shells and
Bound states of dipolar molecules studied with the Berggren expansion method
Bound states of dipole-bound negative anions are studied by using a
non-adiabatic pseudopotential method and the Berggren expansion involving bound
states, decaying resonant states, and non-resonant scattering continuum. The
method is benchmarked by using the traditional technique of direct integration
of coupled channel equations. A good agreement between the two methods has been
found for well-bound states. For weakly-bound subthreshold states with binding
energies comparable with rotational energies of the anion, the direct
integration approach breaks down and the Berggren expansion method becomes the
tool of choice.Comment: 12 pages, 10 figure
Nuclear rotation in the continuum
Atomic nuclei often exhibit collective
rotational-like behavior in highly excited states, well above the particle
emission threshold. What determines the existence of collective motion in the
continuum region, is not fully understood.
In this work, by studying the collective rotation of
the positive-parity deformed configurations of the one-neutron halo nucleus
Be, we assess different mechanisms that stabilize collective behavior
beyond the limits of particle stability.
To solve a particle-plus-core problem, we employ a
non-adiabatic coupled-channel formalism and the Berggren single-particle
ensemble, which explicitly contains bound states, narrow resonances, and the
scattering continuum. We study the valence-neutron density in the intrinsic
rotor frame to assess the validity of the adiabatic approach as the excitation
energy increases.
We demonstrate that collective rotation of the ground
band of Be is stabilized by (i) the fact that the one-neutron
decay channel is closed, and (ii) the angular momentum alignment, which
increases the parentage of high- components at high spins; both effects
act in concert to decrease decay widths of ground-state band members. This is
not the case for higher-lying states of Be, where the
neutron-decay channel is open and often dominates.
We demonstrate that long-lived collective states can
exist at high excitation energy in weakly bound neutron drip-line nuclei such
as Be
Description of the proton and neutron radiative capture reactions in the Gamow shell model
We formulate the Gamow shell model (GSM) in coupled-channel (CC)
representation for the description of proton/neutron radiative capture
reactions and present the first application of this new formalism for the
calculation of cross-sections in mirror reactions 7Be(p,gamma)8B and
7Li(n,gamma)8Li. The GSM-CC formalism is applied to a translationally-invariant
Hamiltonian with an effective finite-range two-body interaction. Reactions
channels are built by GSM wave functions for the ground state 3/2- and the
first excited state 1/2- of 7Be/7Li and the proton/neutron wave function
expanded in different partial waves
Gamow shell model description of radiative capture reactions LiBe and LiLi
According to standard stellar evolution, lithium abundance is believed to be
a useful indicator of the stellar age. However, many evolved stars like red
giants show huge fluctuations around expected theoretical abundances that are
not yet fully understood. The better knowledge of nuclear reactions that
contribute to the creation and destruction of lithium can help to solve this
puzzle. In this work we apply the Gamow shell model (GSM) formulated in the
coupled-channel representation (GSM-CC) to investigate the mirror radiative
capture reactions LiBe and LiLi. The
cross-sections are calculated using a translationally invariant Hamiltonian
with the finite-range interaction which is adjusted to reproduce spectra,
binding energies and one-nucleon separation energies in Li, Be. All
relevant , , and transitions from the initial continuum states to
the final bound states and of Li and Be are
included. We demonstrate that the -wave radiative capture of proton
(neutron) to the first excited state of Be (Li) is
crucial and increases the total astrophysical -factor by about 40 \%.Comment: arXiv admin note: text overlap with arXiv:1502.0163
Bound and resonance states of the dipolar anion of hydrogen cyanide: competition between threshold effects and rotation in an open quantum system
Bound and resonance states of the dipole-bound anion of hydrogen cyanide
HCN are studied using a non-adiabatic pseudopotential method and the
Berggren expansion technique involving bound states, decaying resonant states,
and non-resonant scattering continuum. We devise an algorithm to identify the
resonant states in the complex energy plane. To characterize spatial
distributions of electronic wave functions, we introduce the body-fixed density
and use it to assign families of resonant states into collective rotational
bands. We find that the non-adiabatic coupling of electronic motion to
molecular rotation results in a transition from the strong-coupling to
weak-coupling regime. In the strong coupling limit, the electron moving in a
subthreshold, spatially extended halo state follows the rotational motion of
the molecule. Above the ionization threshold, electron's motion in a resonance
state becomes largely decoupled from molecular rotation. Widths of
resonance-band members depend primarily on the electron orbital angular
momentum.Comment: 11 pages, 13 figure