305 research outputs found
Bayesian averaging for ground state masses of atomic nuclei in a Machine Learning approach
We present global predictions of the ground state mass of atomic nuclei based
on a novel Machine Learning (ML) algorithm. We combine precision nuclear
experimental measurements together with theoretical predictions of unmeasured
nuclei. This hybrid data set is used to train a probabilistic neural network.
In addition to training on this data, a physics-based loss function is employed
to help refine the solutions. The resultant Bayesian averaged predictions have
excellent performance compared to the testing set and come with well-quantified
uncertainties which are critical for contemporary scientific applications. We
assess extrapolations of the model's predictions and estimate the growth of
uncertainties in the region far from measurements.Comment: 15 pages, 10 figures, comments welcom
Constraining inputs to realistic kilonova simulations through comparison to observed -process abundances
Kilonovae, one source of electromagnetic emission associated with neutron
star mergers, are powered by the decay of radioactive isotopes in the
neutron-rich merger ejecta. Models for kilonova emission consistent with the
electromagnetic counterpart to GW170817 predict characteristic abundance
patterns, determined by the relative balance of different types of material in
the outflow. Assuming the observed source is prototypical, this inferred
abundance pattern in turn must match -process abundances deduced by other
means, such as what is observed in the solar system. We report on analysis
comparing the input mass-weighted elemental compositions adopted in our
radiative transfer simulations to the mass fractions of elements in the Sun, as
a practical prototype for the potentially universal abundance signature from
neutron-star mergers. We characterize the extent to which our parameter
inference results depend on our assumed composition for the dynamical and wind
ejecta and examine how the new results compare to previous work. We find that a
dynamical ejecta composition calculated using the FRDM2012 nuclear mass and
FRLDM fission models with extremely neutron-rich ejecta ()
along with moderately neutron-rich () wind ejecta composition
yields a wind-to-dynamical mass ratio of = 0.47 which
best matches the observed AT2017gfo kilonova light curves while also producing
the best-matching abundance of neutron-capture elements in the solar system.Comment: 16 pages, 9 figures, submitted to PR
Executive Summary of the Topical Program: Nuclear Isomers in the Era of FRIB
We report on the Facility for Rare Isotope Beams (FRIB) Theory Alliance
topical program "Nuclear Isomers in the Era of FRIB". We outline the many ways
isomers influence and contribute to nuclear science and technology, especially
in the four FRIB pillars: properties of rare isotopes, nuclear astrophysics,
fundamental symmetries, and applications for the nation and society. We
conclude with a resolution stating our recommendation that the nuclear physics
community actively pursue isomer research. A white paper is forthcoming.Comment: 4 pages including reference
First application of mass measurement with the Rare-RI Ring reveals the solar r-process abundance trend at A=122 and A=123
The Rare-RI Ring (R3) is a recently commissioned cyclotron-like storage ring
mass spectrometer dedicated to mass measurements of exotic nuclei far from
stability at Radioactive Isotope Beam Factory (RIBF) in RIKEN. The first
application of mass measurement using the R3 mass spectrometer at RIBF is
reported. Rare isotopes produced at RIBF, Sn, In, Cd,
Ag, Pd, were injected in R3. Masses of In, Cd,
and Pd were measured whereby the mass uncertainty of Pd was
improved. This is the first reported measurement with a new storage ring mass
spectrometery technique realized at a heavy-ion cyclotron and employing
individual injection of the pre-identified rare nuclei. The latter is essential
for the future mass measurements of the rarest isotopes produced at RIBF. The
impact of the new Pd result on the solar -process abundances in a
neutron star merger event is investigated by performing reaction network
calculations of 20 trajectories with varying electron fraction . It is
found that the neutron capture cross section on Pd increases by a
factor of 2.2 and -delayed neutron emission probability,
, of Rh increases by 14\%. The neutron capture cross
section on Pd decreases by a factor of 2.6 leading to pileup of
material at , thus reproducing the trend of the solar -process
abundances. The trend of the two-neutron separation energies (S)
was investigated for the Pd isotopic chain. The new mass measurement with
improved uncertainty excludes large changes of the S value at
. Such large increase of the S values before was
proposed as an alternative to the quenching of the shell gap to
reproduce -process abundances in the mass region of
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