[RIBF ULIC mini-WS]
Structure of neutron-richmatter revealed by beta decay
Monday, 29 July 2024 - Tuesday, 30 July 2024

Book of Abstracts

iiContents
Beyond mean field approach for beta decay . . . . . . . . . . . . . . . . . . . . . . . . . .

1Large-scale shell model study of β − -decay properties of N = 126, 125 nuclei along the
r-process path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

Nuclear spectroscopy of the nuclei in the vicinity of N = 126 at KISS . . . . . . . . . . .

1

Recent progress and attempts to describe beta decay based on nuclear DFT . . . . . . . .

2

Perspectives for next beta-decay and delayed-neutron data table . . . . . . . . . . . . . .

2Introduction: Challenges to nuclear theory of beta decay . . . . . . . . . . . . . . . . . .

2[online] Sensitivity studies of the r-process rare-earth peak abundances to nuclear masses
and beta-decay half-lives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Test of segmented plastic implantation detector with RI beam at RIBF . . . . . . . . . . .

3

Decay spectroscopy results from EURICA and future perspective of IDATEN . . . . . . .

3[online] Why beta delayed neutrons matter⋯ . . . . . . . . . . . . . . . . . . . . . . . .

4[online] Recent progress in studying β-delayed neutron emission . . . . . . . . . . . . .

4Shape Coexistence and Shape Evolution in Neutron-Rich Nuclei Studied by Beta Decay .

5

Can nuclear physics solve the ”missing gold problem” in the evolution of Galaxy? . . . .

5

RI experiment for the r-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

Summary and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Beta-decay in heavy neutron-rich nuclei . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Research opportunities of heavy neutron-rich nuclei with DTAS at RIBF: TATAKI-Pro .

6

Half-life and beta-delayed neutron emission measurements of N ∼ 126 neutron-rich nuclei
by BRIKEN at RIBF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7[online] Experimental Beta-Decay Half-Lives and Beta-Delayed Neutron Emission Probabilities in Medium-Mass Nuclei (A ∼ 110) . . . . . . . . . . . . . . . . . . . . . . . . 7

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[RIBF ULIC mini-WS] Structure of neutron-rich matter revealed by beta … / Book of Abstracts
Session 2 / 1

Beyond mean field approach for beta decay
Author: HIROYUKI SAGAWANone
Corresponding Author: sagawa@ribf.riken.jp

We study beta decay by using beyond mean field model so called Subtracted second RPA model
including 2-particle-2hole configurations on top of 1p-1h configuration. We study also the effect of
tensor correlations in beta decay process.

Session 4 / 2

Large-scale shell model study of β − -decay properties of N = 126, 125
nuclei along the r-process path
Author: ANIL KUMAR1
Co-authors: Cenxi Yuan 2 ; Noritaka Shimizu 1 ; Praveen C. Srivastava 3 ; Yutaka Utsuno 4
1

Center for Computational Sciences, University of Tsukuba, Tsukuba

2

Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, Zhuhai, Guangdong, China

3

Deaprtment of Physics, IIT Roorkee, India

4

Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan and Center for Nuclear
Study, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan

Corresponding Author: anil@nucl.ph.tsukuba.ac.jp

The rapid neutron capture process (r-process) is the most important mechanism for the synthesisof about half of the elements heavier than iron. It occurs in an environment with relatively hightemperatures and high neutron densities. The abundances of the elements created by the r-processstrongly depend on several nuclear inputs like masses, neutron capture rates, β-decay rates, andβ-delayed neutron emission probabilities at the waiting point nuclei. Among them, the β-decay
process is crucial in the r-process. In this work, we have investigated various nuclear β-decay
properties of N = 126, 125 isotones with proton numbers Z = 52 − 79 within the framework of
the nuclear shell model. This comprehensive analysis considered both Gamow-Teller (GT) and firstforbidden (FF) transitions to evaluate β-decay rates. We have found that including FF transitions inaddition to GT transitions is essential, as they significantly impact the total β-decay half-lives near
Z = 82. Additionally, we systematically analyzed the GT strength distributions as a function of
proton number. We have observed that the GT strengths at low excitation energies are rather strongon the proton deficient side due to the increasing number of proton holes in the proton 0h11/2
orbit, which accelerates GT decay. This investigation aims to provide detailed information on βdecay properties around A ≈ 195 to understand the distribution of the third r-process abundance
peak.

Session 4 / 3

Nuclear spectroscopy of the nuclei in the vicinity of N = 126 at
KISS
Author: Yoshikazu HIRAYAMA1
1

IPNS, KEK

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Corresponding Author: yoshikazu.hirayama@kek.jp

The study of the β-decay half-lives and massees of waiting-point nuclei with N = 126 is crucial
to understand the explosive astrophysical environment for the formation of the third peak in theobserved solar abundance pattern, which is produced by a rapid neutron capture process (r-process).
However, the half-life and mass measurements of the waiting-point nuclei remain impracticable dueto the difficulty in the production of the nuclei. Therefore, accurate theoretical predictions for thehalf-lives and masses are required for investigations of astrophysical environments. It is essential
to perform nuclear spectroscopy for investigating β-decay schemes including spin-parity values,
nuclear wave-functions and interactions, and nuclear masses in this heavy region for more precise
predictions.
For the nuclear spectroscopy, we developed KEK Isotope Separation System (KISS). The nuclei inthe vicinity of N = 126 are produced by multi-nucleon transfer reactions (MNT) of 136 Xe beam
(10.75 MeV/A) impinging upon a 198 Pt target. Thanks to newly developed doughnut-shaped gas
cell, the extraction yields of the reaction products increased by more than one order of magnitude.
This system enabled us to successfully perform bg-decay spectroscopy, in-gas-cell laser ionization
spectroscopy, and mass measurements by using MRTOF-MS. To promote these nuclear spectroscopy,
we started KISS-1.5/2 project to upgrade the KISS facility to provide more exotic RI beam.
In the presentation, we will report the present status of KISS, experimental results of nuclear spectroscopy in the heavy region, and future plan.

Session 2 / 4

Recent progress and attempts to describe beta decay based on nuclear DFT
Author: Nobuo HINOHARA1
1

Center for Computational Sciences, University of Tsukuba

Corresponding Author: hinohara@nucl.ph.tsukuba.ac.jp-

Session 4 / 5

Perspectives for next beta-decay and delayed-neutron data table
Author: Futoshi Minato1
1

Kyushu university

Corresponding Author: minato.futoshi.009@m.kyushu-u.ac.jp

TBA

Session 1 / 6Introduction: Challenges to nuclear theory of beta decay
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Author: Kenichi Yoshida1
1

Osaka University

Corresponding Author: kyoshida@rcnp.osaka-u.ac.jp

I will discuss the roles of nuclear structure on the beta decay in the framework of DFT.

Session 3 / 7[online] Sensitivity studies of the r-process rare-earth peak abundances to nuclear masses and beta-decay half-lives
Author: Yifei Niu1
1

Lanzhou University

Corresponding Author: niuyf@lzu.edu.cn

The sensitivities of the r-process rare-earth peak abundances to nuclear masses and beta-decay halflives have been studied in different astrophysical scenarios. The most impactful nuclei are identified
by varying nuclear masses and beta-decay half-lives, respectively. The impacts of nuclear mass aswell as β-decay rate of an individual nucleus on the r-process rare-earth peak abundances are analyzed. The role of fission is discussed in details. This work provides recommended targets for future
researches and thus helps to increase the understanding of rare-earth peak formation mechanism
and the efficacy of the rare-earth peak as an r -process site diagnostic.

Session 2 / 8

Test of segmented plastic implantation detector with RI beam at
RIBF
Author: Quanbo Zeng1
1

RIKEN

Corresponding Author: quanbo.zeng@riken.jp

The segmented plastic scintillation detector GARi was tested with RI beam in the focal plain F11of the RIBF accelerator complex. Implantation-decay correlation was obtained based on the reconstructed ion and beta positions on GARi. Known half-lifes in neutron-rich Ar region were used tovalidate the implantation-decay correlation. Additionally, several new half-lives in this region were
measured for the first time.

Session 4 / 9

Decay spectroscopy results from EURICA and future perspectiveof IDATEN
Author: Byul Moon1
1

Center for Exotic Nuclear Studies, Institute for Basic Science

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Corresponding Author: mb0316@ibs.re.kr

In this talk, the some experimental results from the previous decay spectroscopy carried out at RIBF,
EURICA (EUROBALL-RIKEN Cluster Array), will be introduced. These results are mostly from theneutron-rich isotope beyond the doubly-magic 132 Sn nucleus, which are important for the r-process
nucleosynthesis scenario. New nuclear structure observables will be presented with the theoreticalpredictions.
In addition, a newly initiated international collaboration, IDATEN (International Detector Assembly for fast-Timing measurements of Exotic Nuclei) will be also introduced. The IDATEN is theworld-largest fast-timing γ-ray detection system comprised of 82 LaBr3 (Ce) detectors for decay spectroscopy and a commissioning experiment was recently carried out at RIBF. Preliminary results fromthis experiment will be presented and the future perspective will be given in this talk.

Session 2 / 10

[online] Why beta delayed neutrons matter⋯
Author: Alejandro Algora1
1

IFIC (CSIC-Univ. Valencia)

Corresponding Author: algora@ific.uv.es

Discovered by Roberts et al. beta delayed neutrons are very relevant in reactor control, nuclear
astrophysics and nuclear structure. Beta delayed neutron emission is a process that become morea more dominant as we move far away from stability, so its study is crucial for understanding thenuclear structure of very exotic neutron rich nuclei. In this talk, I will present how it is possible
to infer nuclear shapes from Pn and T1/2 measurements and why it is relevant to combine neutron
spectroscopic measurements with total absorption studies.

Session 3 / 11

[online] Recent progress in studying β-delayed neutron emission
Authors: Zhengyu Xu1 ; Robert Grzywacz1 ; Miguel Madurga1
1

University of Tennessee KnoxvilleCorresponding Authors: mmadurga@utk.edu, zxu41@utk.edu, rgrzywac@utk.edu

β-delayed neutron emission is a common and dominating decay process for most of the neutronrich nuclei far from the stability line. Experimental investigations on β-delayed neutrons are ofgreat significance in a large variety of fields, including nuclear physics, astrophysics, and industrial
applications. First, it is a sensitive probe to the β-decay feedings above neutron separation energy,
which is related to the nuclear structures of parent and daughter nuclei. Second, the decay processitself carries fundamental information on how neutron unbound states are formed in β decay. Owing
to its importance, rapid progress has been made in measuring β-delayed neutron emission, either
inclusive or exclusive, at many different radioactive ion-beam facilities in the last decade. In thiscontribution, I will present a few highlights of our recent experimental effort in studying β-delayed
neutrons in a range of nuclei with mass numbers A = 24 ∼ 132. The experimental findings werecompared with various theoretical models, gaining valuable insights into the shell evolution in exotic
nuclei as well as the statistical/nonstatistical natures of β-delayed neutron emission in mediumheavy and heavy isotopes.
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Session 4 / 12

Shape Coexistence and Shape Evolution in Neutron-Rich Nuclei
Studied by Beta Decay
Author: Atsuko Odahara1
1

Department of Physics, Osaka University

Corresponding Author: odahara@phys.sci.osaka-u.ac.jp

We have been systematically studying shape coexistence and shape evolution in neutron-rich nuclei.
These are one of the important subjects to understand appearance of variety of nuclear structure
as increase of neutron and proton numbers. We have studied change of nuclear structure by the βdecay in wide isospin region such as neutron-rich Mg and Al isotopes close to ‘Island of Inversion(IoI)’and neutron-rich A ~ 140 nuclei, which are located in the northeast region of the doubly-magic
nucleus on the nuclear chart.
In the former case, experiments have been performed by using spin-polarized beam at TRIUMF witheffectiveness to unambiguously assign the spins and parities of the states in daughter nucleus bymeasuring the β-decay spatial asymmetry of the spin-polarized isotope. We have been systematically studying shape coexistence and shell evolution of neutron-rich nuclei in and around the N =20 IoI.
In the latter case, the experiment was performed as one in EURICA campaign at BigRIPS in RIKEN.
Nuclear structure gradually changes from spherical (single-particle like) shape in nuclei close to the
doubly-magic 132Sn to deformed (collective like) shape for nuclei located in transitional region withincreasing neutron and proton number. Additionally, octupole correlation can be observed in nuclei
around 144Ba (Z=56 and N=88). Namely, we a variety of structure, such as prolate deformation andvibrational states (octupole band, beta band, and gamma band) can be observed in low-lying states.
In this workshop, I will talk mainly results of EURICA experiment about nuclear structure of 141−144 Xe
nuclei by the beta decay of 141−144 I as well as results of TRIUMF experiments.

Session 3 / 13

Can nuclear physics solve the ”missing gold problem” in the evolution of Galaxy?
Author: Nobuya Nishimura1
1

RIKEN

Corresponding Author: nobuya@cns.s.u-tokyo.ac.jp

Understanding neutron-rich unstable nuclei is crucial for investigating the r-process nucleosynthesis.
In particular, the β decay of the N = 126 isotones is decisive for the production of the third peak,including gold and platinum. In this talk, based on nucleosynthesis uncertainty calculations, I will
discuss the possibility of addressing the “missing gold problem” in the galactic chemical evolution
study by improving the β-decay half-live of N = 126 nuclei.

Session 1 / 14

RI experiment for the r-process
Author: Shunji Nishimura1
1

RIKEN Nishina Center

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Corresponding Author: nishimu@riken.jp

RI experiment for the r-process

Session 4 / 15

Summary and discussion
Author: Wataru Horiuchi1
1Osaka Metropolitan University

Corresponding Author: whoriuchi@omu.ac.jp

Summary and discussion

Session 3 / 16

Beta-decay in heavy neutron-rich nuclei
Author: Toru Sato1
1

RCNP, Osaka University

Corresponding Author: tsato@rcnp.osaka-u.ac.jp

Beta-decay in heavy neutron-rich nuclei

Session 3 / 17

Research opportunities of heavy neutron-rich nuclei with DTAS
at RIBF: TATAKI-Pro
Author: Anabel Morales1
1

IFIC

Corresponding Author: aimolo@ific.uv.es

Exploring the heavy neutron-rich region around and beyond N = 126 is one of the major aimsof nuclear facilities worldwide. The foremost reason is understanding the nucleosynthesis of theheaviest elements existing in nature, formed only by the rapid neutron-capture process. At thethird waiting point, the only observable measured systematically up to date —some β half-lives nearstability— reveals the largest discrepancies among the models used to calculate nuclear inputs for
r-process simulations. Measuring observables better suited to obtain detailed structural informationin nuclei with few tens of neutron above N = 126 or protons below Z = 82, is key to obtain higherquality calculated nuclear inputs getting far away from stability, in the inaccessible regions of the
r-process reaction path. In this talk, the potential of the TATAKI-Pro setup at RIBF, consisting of
the WAS3ABi active stopper and the Decay Total Absorption Spectrometer DTAS, will be discussed.
The main advantage of the latter is the possibility to use it simultaneously as a calorimeter to measure β-strength functions, and as a segmented γ array to measure key structural properties such as
isomeric states, nuclear lifetimes, decay schemes, and, in combination with WAS3ABi, Meitner-Ellis
electrons.
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Session 2 / 18

Half-life and beta-delayed neutron emission measurements ofN ∼ 126 neutron-rich nuclei by BRIKEN at RIBF
Author: Tik Tsun Yeung1
1

The University of Tokyo

Corresponding Author: yeung@nex.phys.s.u-tokyo.ac.jp

The neutron-rich N ∼ 126 region is important to r-process calculations, but difficult to be accessedby experiments. This region is unique for its strong competition between allowed and first-forbidden
transitions, which complicates half-life predictions. Besides, the abundances of the third r-process
peak elements and actinides are sensitive to half-lives of N = 126 isotones. Measurements of more
exotic nuclei are essential to benchmark theoretical models commonly used in r-process calculations. We will present results from the BRIKEN experiment, which is the first attempt to investigate
N ∼ 126 nuclei at RIBF. Particle identification was confirmed by the BigRIPS separator and a silicon energy-loss telescope. Charged-particle decay and neutron emission were measured by the
WAS3ABi beta-counting system and the BRIKEN neutron counter. Half-lives and beta-delayed neutron emission probabilities (Pn ) of N ∼ 126 exotic isotopes were determined. Several of which werefirst measurements. Preliminary results of Z
leqq79 isotopes will be discussed.

Session 1 / 19

[online] Experimental Beta-Decay Half-Lives and Beta-Delayed
Neutron Emission Probabilities in Medium-Mass Nuclei (A ∼ 110)
Author: Vi Phong11Radioactive Isotope Physics Laboratory, RIKEN Nishina Center

Corresponding Author: phong@ribf.riken.jp

beta-delayed neutrons

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