9,823 research outputs found

### Nuclear mass predictions based on Bayesian neural network approach with pairing and shell effects

Bayesian neural network (BNN) approach is employed to improve the nuclear
mass predictions of various models. It is found that the noise error in the
likelihood function plays an important role in the predictive performance of
the BNN approach. By including a distribution for the noise error, an
appropriate value can be found automatically in the sampling process, which
optimizes the nuclear mass predictions. Furthermore, two quantities related to
nuclear pairing and shell effects are added to the input layer in addition to
the proton and mass numbers. As a result, the theoretical accuracies are
significantly improved not only for nuclear masses but also for single-nucleon
separation energies. Due to the inclusion of the shell effect, in the unknown
region, the BNN approach predicts a similar shell-correction structure to that
in the known region, e.g., the predictions of underestimation of nuclear mass
around the magic numbers in the relativistic mean-field model. This manifests
that better predictive performance can be achieved if more physical features
are included in the BNN approach.Comment: 15 pages, 4 figures, and 3 table

### Self-consistent relativistic quasiparticle random-phase approximation and its applications to charge-exchange excitations and $\beta$-decay half-lives

The self-consistent quasiparticle random-phase approximation (QRPA) approach
is formulated in the canonical single-nucleon basis of the relativistic
Hatree-Fock-Bogoliubov (RHFB) theory. This approach is applied to study the
isobaric analog states (IAS) and Gamov-Teller resonances (GTR) by taking Sn
isotopes as examples. It is found that self-consistent treatment of the
particle-particle residual interaction is essential to concentrate the IAS in a
single peak for open-shell nuclei and the Coulomb exchange term is very
important to predict the IAS energies. For the GTR, the isovector pairing can
increase the calculated GTR energy, while the isoscalar pairing has an
important influence on the low-lying tail of the GT transition. Furthermore,
the QRPA approach is employed to predict nuclear $\beta$-decay half-lives. With
an isospin-dependent pairing interaction in the isoscalar channel, the
RHFB+QRPA approach almost completely reproduces the experimental $\beta$-decay
half-lives for nuclei up to the Sn isotopes with half-lives smaller than one
second. Large discrepancies are found for the Ni, Zn, and Ge isotopes with
neutron number smaller than $50$, as well as the Sn isotopes with neutron
number smaller than $82$. The potential reasons for these discrepancies are
discussed in detail.Comment: 34 pages, 14 figure

### Nuclear $\beta^+$/EC decays in covariant density functional theory and the impact of isoscalar proton-neutron pairing

Self-consistent proton-neutron quasiparticle random phase approximation based
on the spherical nonlinear point-coupling relativistic Hartree-Bogoliubov
theory is established and used to investigate the $\beta^+$/EC-decay half-lives
of neutron-deficient Ar, Ca, Ti, Fe, Ni, Zn, Cd, and Sn isotopes. The isoscalar
proton-neutron pairing is found to play an important role in reducing the decay
half-lives, which is consistent with the same mechanism in the $\beta$ decays
of neutron-rich nuclei. The experimental $\beta^+$/EC-decay half-lives can be
well reproduced by a universal isoscalar proton-neutron pairing strength.Comment: 12 pages, 4 figure

### $\beta$-decay half-lives of neutron-rich nuclei and matter flow in the $r$-process

The $\beta$-decay half-lives of neutron-rich nuclei with $20 \leqslant Z
\leqslant 50$ are systematically investigated using the newly developed fully
self-consistent proton-neutron quasiparticle random phase approximation (QRPA),
based on the spherical relativistic Hartree-Fock-Bogoliubov (RHFB) framework.
Available data are reproduced by including an isospin-dependent proton-neutron
pairing interaction in the isoscalar channel of the RHFB+QRPA model. With the
calculated $\beta$-decay half-lives of neutron-rich nuclei a remarkable
speeding up of $r$-matter flow is predicted. This leads to enhanced $r$-process
abundances of elements with $A \gtrsim 140$, an important result for the
understanding of the origin of heavy elements in the universe.Comment: 14 pages, 4 figure

### Reexamining the temperature and neutron density conditions for r-process nucleosynthesis with augmented nuclear mass models

We explore the effects of nuclear masses on the temperature and neutron
density conditions required for r-process nucleosynthesis using four nuclear
mass models augmented by the latest atomic mass evaluation. For each model we
derive the conditions for producing the observed abundance peaks at mass
numbers A ~ 80, 130, and 195 under the waiting-point approximation and further
determine the sets of conditions that can best reproduce the r-process
abundance patterns (r-patterns) inferred for the solar system and observed in
metal-poor stars of the Milky Way halo. In broad agreement with previous
studies, we find that (1) the conditions for producing abundance peaks at A ~
80 and 195 tend to be very different, which suggests that, at least for some
nuclear mass models, these two peaks are not produced simultaneously; (2) the
typical conditions required by the critical waiting-point (CWP) nuclei with the
N = 126 closed neutron shell overlap significantly with those required by the
N=82 CWP nuclei, which enables coproduction of abundance peaks at A ~ 130 and
195 in accordance with observations of many metal-poor stars; and (3) the
typical conditions required by the N = 82 CWP nuclei can reproduce the
r-pattern observed in the metal-poor star HD 122563, which differs greatly from
the solar r-pattern. We also examine how nuclear mass uncertainties affect the
conditions required for the r-process and identify some key nuclei
including76Ni to 78Ni, 82Zn, 131Cd, and 132Cd for precise mass measurements at
rare-isotope beam facilities.Comment: 28 pages,9 figures,1 tabl

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