883 research outputs found
Thomas-Ehrman effect in a three-body model: Ne case
The dynamic mechanism of the Thomas-Ehrman shift is studied in three-cluster
systems by example of Ne and C isobaric mirror partners. We
predict configuration mixings for and states in Ne and
C. Large isospin symmetry breaking on the level of wave function
component weights is demonstrated for these states and discussed as three-body
mechanism of Thomas-Ehrman shift. It is shown that the description of the
Coulomb displacement energies requires a consistency among three parameters:
the Ne decay energy , the F ground state energy , and
the configuration mixing parameters for the Ne/C and
states. Basing on this analysis we infer the F ground state
energy to be MeV.Comment: 10 pages 8 figure
Pauli-principle driven correlations in four-neutron nuclear decays
Mechanism of simultaneous non-sequential four-neutron () emission (or
`true' -decay) has been considered in phenomenological five-body approach.
This approach is analogous to the model of the direct decay to the continuum
often applied to - and -decays. It is demonstrated that -decay
fragments should have specific energy and angular correlations reflecting
strong spatial correlations of `valence' nucleons orbiting in their
-precursors. Due to the Pauli exclusion principle, the valence neutrons are
pushed to the symmetry-allowed configurations in the -precursor structure,
which causes a `Pauli focusing' effect. Prospects of the observation of the
Pauli focusing have been considered for the -precursors H and O.
Fingerprints of their nuclear structure or/and decay dynamics are predicted
Anomalous population of He states in reactions with Li
Structure with the lowest energy observed in the He spectrum populated
in the proton knockout reaction with Li beam has a peak at
MeV. This peak is usually interpreted as a resonant ground state of
He. Our theoretical calculations indicate that this peak is likely to be
a pileup of , , and excitations with very similar shapes. %We
predict a very specific nature of the excitation in He. Moreover,
the ``soft'' excitation appears to be the lowest one in energy. Such an
anomalous continuum response is traced to the halo structure of Li
providing extreme low energy shift to all the expected continuum excitations.
Competitions of the initial state structure (ISS) and the final state
interaction (FSI) effects on the spectrum and three-body correlations in
He are discussed. Analogous effect of the extreme low-energy shift could
also be expected in other cases of emitters populated in reactions with
halo nuclei. Simplified example of the He spectrum in knockout
from Be, is given. We also discuss limits on the properties of He
stemming from the observed He spectrum.Comment: 10 pages, 13 figure
Possibility to study a two-proton halo in Ne
The nuclide Ne is studied theoretically in a three-body
O++ model. We demonstrate that the experimental condition for
existence of a proton halo in Ne can be reasonably quantified in terms
of configuration mixing. We discuss experimental evidences for a proton
halo in Ne. We define which kind of experimental data could elucidate
this issue.Comment: 5 pages, 5 figure
Problems with interpretation of He ground state
The continuum of He nucleus is studied theoretically in a three-body
He++ model basing on the recent information concerning He
spectrum [Golovkov, \textit{et al.}, Phys. Rev. C \textbf{76}, 021605(R)
(2007)]. The He ground state (g.s.) candidate with structure
for new g.s. energy of He is predicted to be at about
MeV. The peak in the cross section associated with this state may be
shifted to a lower energy (e.g. MeV) when He is populated in
reactions with Li due to peculiar reaction mechanism. Formation of the
low-energy ( keV) ``alternative'' ground state with structure
is highly probable in He in the case of considerable
attraction (e.g. fm) in the s-wave He channel, which properties are
still quite uncertain. This result either questions the existing experimental
low-energy spectrum of He or place a limit on the scattering length in
He channel, which contradicts existing data.Comment: 14 pages, 13 figures, 1 tabl
Decay mechanism and lifetime of Kr
The lifetime of the recently discovered emitter Kr was recently
found considerably below the lower limit predicted theoretically. This
communication addresses this issue.Different separation energy systematics are
analyzed and different mechanisms for emission are evaluated. It is found
that the most plausible reason for this disagreement is a decay mechanism of
Kr, which is not "true " emission, but "transition dynamics" on the
borderline between true and sequential decay mechanisms. If this is
true, this imposes stringent limits MeV on the ground state
energy of Br relative to the Se- threshold.Comment: 7 pages, 8 figure
Two-proton radioactivity and three-body decay. V. Improved momentum distributions
Nowadays quantum-mechanical theory allows one to reliably calculate the
processes of 2p radioactivity (true three-body decays) and the corresponding
energy and angular correlations up to distances of the order of 1000 fm.
However, the precision of modern experiments has now become sufficient to
indicate some deficiency of the predicted theoretical distributions. In this
paper we discuss the extrapolation along the classical trajectories as a method
to improve the convergence of the theoretical energy and angular correlations
at very large distances (of the order of atomic distances), where only the
long-range Coulomb forces are still operating. The precision of this approach
is demonstrated using the "exactly" solvable semianalytical models with
simplified three-body Hamiltonians. It is also demonstrated that for heavy 2p
emitters, the 2p decay momentum distributions can be sensitive to the effect of
the screening by atomic electrons. We compare theoretical results with
available experimental data.Comment: 13 pages, 18 figure
Optimized design of universal two-qubit gates
We construct optimized implementations of the CNOT and other universal
two-qubit gates that, unlike many of the previously proposed protocols, are
carried out in a single step. The new protocols require tunable inter-qubit
couplings but, in return, show a significant improvements in the quality of
gate operations. Our optimization procedure can be further extended to the
combinations of elementary two-qubit as well as irreducible many-qubit gates.Comment: 6 pages, 2 figure
A new class of photo-catalytic materials and a novel principle for efficient water splitting under infrared and visible light - MgB2 as unexpected example
Water splitting is unanimously recognized as environment friendly,
potentially low cost and renewable energy solution based on the future hydrogen
economy. Especially appealing is photo-catalytic water splitting whereby a
suitably chosen catalyst dramatically improves efficiency of the hydrogen
production driven by direct sunlight and allows it to happen even at zero
driving potential. Here, we suggest a new class of stable photo-catalysts and
the corresponding principle for catalytic water splitting in which infrared and
visible light play the main role in producing the photocurrent and hydrogen.
The new class of catalysts based on ionic binary metals with layered
graphite-like structures which effectively absorb visible and infrared light
facilitating the reaction of water splitting, suppress the inverse reaction of
ion recombination by separating ions due to internal electric fields existing
near alternating layers, provide the sites for ion trapping of both polarities,
and finally deliver the electrons and holes required to generate hydrogen and
oxygen gases. As an example, we demonstrate conversion efficiency of 27 percent
at bias voltage bias 0.5 V for magnesium di-boride working as a catalyst for
photo-induced water splitting. We discuss its advantages over some existing
materials and propose the underlying mechanism of photo-catalytic water
splitting by binary layered metals
Transition from direct to sequential two-proton decay in - shell nuclei
Transitions among different mechanisms of two-proton decay are studied in
general. The introduced improved direct-decay model generalizes the
semi-analytical models used before and provides flawless phenomenological
description of three-body correlations in decays. This is demonstrated by
examples of the low-lying Ne state decays. Different forms of transition
dynamic are shown to be highly probable beyond the proton dripline for the
- shell nuclei. It is demonstrated that transition dynamic of
emitters can provide means for extraction of a width of the ground-state
resonance of a core+ subsystem of the core+ system. Practical
applicability of the method is demonstrated by properties of the F
ground state derived from the ^{15}\mbox{Ne}\rightarrow
^{\,13\!\!}\mbox{O}+2p decay data and of the Cl ground state derived
from the ^{30}\mbox{Ar}\rightarrow ^{\,28\!\!}\mbox{S}+2p decay data.Comment: 8 pages, 10 figure
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