II-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

A3-Foresight theory collaboration for nuclear data library: A3LIB
K. Yoshida∗1 for the A3LIB Collaboration
A quantitative understanding of the r-process nucleosynthesis requires nuclear data across the nuclear
chart, including the vicinities of the neutron drip line,
which are experimentally inaccessible. Thus the nuclear theory plays a decisive role to bridge between
nuclear experiments at RI beam facilities and microscopic inputs of the r-process simulation.
The condition of the r-process is given by an astrophysical environment of explosive phenomena withsome possible scenarios. Although nuclear physics thatenters the reaction network may depend on the scenario, the most important nuclear data are the nuclear masses, β-decay properties, and neutron capture
rates;1,2) Given the neutron-number density, temperature, and entropy, the seed nuclei are formed throughthe nuclear statistical equilibrium. Here, the nuclear
masses are a key nuclear physics quantity. When thetemperature decreases in the order of 100 keV, various
nuclear reactions take place, and the neutron-capture
process generates neutron-rich nuclei. If the neutronnumber density is high, it proceeds to the productionof the heaviest nuclei, and ﬁssion occurs. In every process, competition with the β-decay should be considered. The β-decay and the β-delayed neutron emission
play a role in shaping the ﬁnal abundance distributions
observed in nature.
The nuclear energy-density functional (EDF) approach is a possible theoretical model to describe theabove-mentioned nuclear properties in a vast mass region of the nuclear chart in a single framework. Researchers in the A3 (Chine, Japan, and Korea) countries have developed the nuclear EDF method andcomputational techniques. It is natural to start collaboration on the construction of the nuclear data tablenecessary for the r-process modeling and the development of the associated nuclear many-body theory.
I brieﬂy explain a rough plan of the theory collaboration. As shown in Fig. 1, the development of thetheory and model for each nuclear property is stronglyrelated. The key to success is the construction of theEDF. Given the EDF, the binding energy of a nucleus and the single-particle level density are obtainedin a Kohn–Sham scheme. Parallel to an attempt at
the microscopic construction of EDF from an interparticle interaction, a phenomenological constructionis planned in collaboration with the researchers in Korea. The KIDS functional was introduced to better
describe the neutron-star equation of state. We apply
the KIDS functional to open-shell nuclei, where the nucleonic superﬂuidity and shape deformation show up.
Subsequently, the KIDS functional is improved for ﬁ∗1FY

2020

2021

2022

KIDS for mass table

Level densitymicroscopic evaluationtransitions between excited states

β-decay
Fission2024

describing odd-A and odd-odd nuclei

Massn-capture2023

E1 strengths in odd-A nuclei

QRPA and beyond QRPA

extension to odd-A nuclei

fission rates for symmetric fission

spontaneous fission rates for asym. fission

neutron-induced fission

Fig. 1. Plan for the development of A3LIB.

nite nuclei. We developed a novel method for describing odd mass nuclei for a systematic calculation of thenuclear mass. The implementation is performed in theKIDS code.
To describe the neutron capture and β decay rates,
we employ the EDF-based quasiparticle RPA (QRPA).
In neutron-rich nuclei where the neutron separationenergy is approximately a few MeV, the direct capture
process dominates over the compound process. In sucha case, the low-lying excited states and transitions areevaluated microscopically. The description of the transitions among excited states is in progress. For β decay,
we take two approaches: a beyond QRPA method formagic nuclei to describe the spreading eﬀect and theQRPA for deformed nuclei.
The microscopic calculation of the ﬁssion rate is a
big challenge in nuclear theory. The mass parametersand potential energy in the collective (eﬀective) Hamiltonian for ﬁssion are microscopically calculated in an
EDF approach. The ﬁssion rate is then evaluated, e.g.,
by WKB approximation. Hybrid modeling for the ﬁssion yield is planned, where the parameters of the phenomenological model, such as the Langevin approach,are evaluated by a microscopic EDF method.
Finally, the uncertainty quantiﬁcation is essential indeveloping a new generation of the nuclear data table.
The A3LIB is based on the EDF method; thus, all thecalculated quantities are correlated through the coupling constants of EDF. We plan to perform the correlation analysis at each step of the calculation. The
results will be provided in the existing data library online.
References

1) M. R. Mumpower et al., Prog. Part. Nucl. Phys. 86, 86(2016).
2) T. Kajino et al., Prog. Part. Nucl. Phys. 107, 109(2019).

Department of Physics, Kyoto University- 52 -1