125 research outputs found
Exceptional points in the scattering continuum
The manifestation of exceptional points in the scattering continuum of atomic
nucleus is studied using the real-energy continuum shell model. It is shown
that low-energy exceptional points appear for realistic values of coupling to
the continuum and, hence, could be accessible experimentally. Experimental
signatures are proposed which include the jump by of the elastic
scattering phase shift and a salient energy dependence of cross-sections in the
vicinity of the exceptional point.Comment: 7 pages, 9 figure
Near-threshold correlations of neutrons
The appearance of charged-particle clustering in near-threshold configuration
is a phenomenon that can be explained in the Open Quantum System description of
the atomic nucleus. In this work we apply the realistic Shell Model Embedded in
the Continuum to elucidate the emergence of neutron correlations in
near-threshold many-body states coupled to l=1,2 neutron decay channels.
Spectral consequences of such continuum coupling are briefly discussed together
with the emergence of complex multi-neutron correlations.Comment: Invited talk at XXXIII Mazurian Lakes Conference on Physic
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
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
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
Ab-initio No-Core Gamow Shell Model calculations with realistic interactions
No-Core Gamow Shell Model (NCGSM) is applied for the first time to study
selected well-bound and unbound states of helium isotopes. This model is
formulated on the complex energy plane and, by using a complete Berggren
ensemble, treats bound, resonant, and scattering states on equal footing. We
use the Density Matrix Renormalization Group method to solve the many-body
Schr\"{o}dinger equation. To test the validity of our approach, we benchmarked
the NCGSM results against Faddeev and Faddeev-Yakubovsky exact calculations for
H and He nuclei. We also performed {\textit ab initio} NCGSM
calculations for the unstable nucleus He and determined the ground state
energy and decay width, starting from a realistic NLO chiral interaction.Comment: 17 pages, 14 figures. Revised version. Discussion on microscopic
overlap functions, SFs and ANCs is added. Added references. Accepted for
publication at PR
Description of the proton-decaying 0 resonance of the particle
The recent precise experimental determination of the monopole transition form
factor from the ground state of He to its resonance via electron
scattering has reinvigorated discussions about the nature of this first excited
state of the particle. The state has been traditionally
interpreted in the literature as the isoscalar monopole resonance (breathing
mode) or, alternatively, as a particle-hole shell-model excitation. To better
understand the nature of this state, which lies only 410 keV above the
proton emission threshold, we employ the coupled-channel representation of the
no-core Gamow shell model. By considering the H, He,
and H+H] reaction channels, we explain the excitation energy and
monopole form-factor of the state. We argue that the continuum coupling
strongly impacts the nature of this state, which carries characteristics of the
proton decay threshold.Comment: 5 pages, 2 figure
Near-threshold resonances in 11C and the 10B(p,{\alpha})7Be aneutronic reaction cross section
The nucleus 11C plays an important role in the boron-proton fusion reactor
environment as a catalyzer of the 10B(p,{\alpha})7Be reaction which, by
producing a long-lived isotope of 7Be, poisons the aneutronic fusion process
11B(p,2{\alpha})4He. The low-energy cross section of 10B(p,{\alpha})7Be depends
on the near-threshold states 7/2+1 , 5/2+2 , 5/2+3 in 11C whose properties are
primarily known from the indirect measurements. We investigate the
continuum-coupling induced collectivization of these resonances in the shell
model embedded in the continuum. We predict a significant enhancement of the
10B(p,{\alpha})7Be cross section at energies accessible to the laser-driven hot
plasma facilities.Comment: 4 pages, 2 figure
and decay of the Be neutron halo ground state
Beta-delayed proton emission from the neutron halo ground state of Be
raised much attention due to the unusually high decay rate. It was argued that
this may be due to the existence of a resonance just above the proton decay
threshold. In this Letter, we use the lenses of real-energy continuum shell
model to describe several observables including the Gamow-Teller rates for the
-delayed and proton decays, and argue that, within our model,
the large branching ratio cannot be reconciled with other
data.Comment: 5 pages, 3 figure
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
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