1,364 research outputs found
Exploring manifestation and nature of a dineutron in two-neutron emission using a dynamical dineutron model
Emission of two neutrons or two protons in reactions and decays is often
discussed in terms of "dineutron" or "diproton" emission. The discussion often
leans intuitively on something described by Migdal-Watson approximation. In
this work we propose a way to formalize situations of dineutron emission. It is
demonstrated that properly formally defined dineutron emission may reveal
properties which are drastically different from those traditionally expected,
and properties which are actually observed in three-body decays.Comment: 11 pages, 11 Figure
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
High precision studies of soft dipole mode in two-neutron halo nuclei: He case
The "soft dipole" E1 strength function is calculated for the transition from
the He ground state to the continuum He++. The
calculations were performed within the hyperspherical harmonics formalism. The
sensitivity of the results to the He ground state structure and to final
state interactions, are analyzed. The large-basis calculations show the
reliably converged results for soft dipole strength function and for momentum
correlations of the ^{6}\mbox{He} \rightarrow \, ^{4}He++ dissociation
products. Transition mechanisms are analyzed based on the momentum
correlations. The comparison with experimental data is provided.Comment: 16 pages, 17 figure
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
Recommended from our members
Assessment of cognitive abilities in multiethnic countries: The case of the Wolof and Mandinka in the Gambia
Background: The use of cognitive tests is increasing in Africa but little is known about how such tests are affected by the great ethnic and linguistic diversity on the continent.
Aim: To assess ethnic and linguistic group differences in cognitive test performance in the West African country of the Gambia and to investigate the sources of these differences.
Samples: Study 1 included 579 participants aged 14–19 years from the Wolof and Mandinka ethnic groups of the Gambia. Study 2 included 41 participants aged 12–18 years from the two ethnic groups.
Methods: Study 1 assessed performance on six cognitive tests. Participants were also asked about their history of education, residence in the city, parental education, and family socio-economic status. Study 2 assessed performance on two versions of the digit span test. Recall of the numbers 1–5 were compared with recall of numbers 1–9 for both the Wolof (who count in base 5) and the Mandinka (who count in base 10).
Results: Study 1 established that Wolof performance was lower than that of the Mandinka on five out of six cognitive tests. In four of these tests, group differences were partially mediated by participation in primary school and migration to the city. Group differences were substantial for the digit span test and were not attenuated by mediating variables. Study 2 found that digit span among the Wolof was shorter than that of the Mandinka for numbers 1–9 but not for numbers 1–5.
Conclusions: Several suggestions are made on how to consider the ethnicity, language, education, and residence (urban vs. rural) of groups when conducting comparative cognitive assessments or collecting normative data
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
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
- …