Ⅵ. ORGANIZATION AND ACTIVITIES OF RNC

RIKEN Accel. Prog. Rep. 56 (2023)

Nuclear Science and Transmutation Research Division
Superheavy Element Research Group
Superheavy Element Device Development Team
1. Abstract

A gas-ﬁlled recoil ion separator has been used as a main experimental device for the study of superheavy elements. This teamis in charge of maintaining, improving, developing, and operating the separators and related devices. In the RIBF facility, three gasﬁlled recoil ion separators are installed at RILAC and RRC facility. One is GARIS that is designed for a symmetric reaction such as
coldfusion reaction, and the other two are developed for an asymmetric reaction such as hot-fusion reaction, GARIS-II and GARIS-III.
New elements 278 113 were produced by 70 Zn + 209 Bi reaction using GARIS. Further the new element search is currently in progressby using GARIS-II and GARIS-III.

2. Major Research Subjects(1) Maintenance of GARIS, GARIS-II and development of new separator GARIS-III(2) Maintenance and development of detector and DAQ system for superheavy element research(3) Maintenance and development of target system for GARIS, GARIS-II and GARIS-III

3. Summary of Research Activity

The GARIS-II and III are newly developed which has an acceptance twice as large as existing GARIS, in order to realize higher
transmission. A new element search program aiming to element 119 was started using GARIS-II. And new separator GARIS-III wasdeveloped and installed into the RILAC experimental hall. After the some commissioning works of GARIS-III, new 119th element
search has been started. We will also oﬀer user-support if a researcher wishes to use the devices for his/her own research program.

Members
Team Leader
Kouji MORIMOTO
Senior Technical Scientists
Masaki FUJIMAKI

Daiya KAJI

Postdoctoral Researchers
Pierre BRIONNET

Sota KIMURA

Visiting Scientists
Shin-ichi GOTO (Niigata Univ.)
Katsuhisa NISHIO (JAEA)
Eiji IDEGUCHI (Osaka Univ.)

Toshitaka NIWASE (KEK)
Yuta ITO (JAEA)
Fuyuki TOKANAI (Yamagata Univ.)

Student Trainee
Kosaku KURAMOTO (Yamagata Univ.)

List of Publications & Presentations
Publications[Original Papers]
P. Brionnet, R. K. Grzywacz, D. Kaji, T. T. King, T. Niwase, K. Morimoto, K. P. Rykaczewski, and H. Sakai, “Development of digitalelectronics for the search of SHE nuclei using GARIS-II/III at RIKEN,” Nucl. Instrum. Methods Phys. Res. A 1049, 168068 (2023).
H. Sakai, H. Haba, K. Morimoto, and N. Sakamoto, “Facility upgrade for superheavy-element research at RIKEN,” Eur. Phys. J. A 58,238 (2022).
M. Tanaka, P. Brionnet, M. Du, J. Ezold, K. Felker, B. J. P. Gall, S. Go, R. K. Grzywacz, H. Haba, K. Hagino, S. Hogle, S. Ishizawa,D. Kaji, S. Kimura, T. T. King, Y. Komori, R. K. Lemon, M. G. Leonard, K. Morimoto, K. Morita, D. Nagae, N. Naito, T. Niwase,
B. C. Rasco, J. B. Roberto, K. P. Rykaczewski, S. Sakaguchi, H. Sakai, Y. Shigekawa, D. W. Stracener, S. VanCleve, Y. Wang,
K. Washiyama, and T. Yokokita, “Probing optimal reaction energy for synthesis of element 119 from 51 V + 248 Cm reaction withquasielastic barrier distribution measurement,” J. Phys. Soc. Jpn. 91, 084201 (2022).
T. Niwase, Y. X. Watanabe, Y. Hirayama, M. Mukai, P. Schury, A. N. Andreyev, T. Hashimoto, S. Iimura, H. Ishiyama, Y. Ito, S. C. Jeong,
D. Kaji, S. Kimura, H. Miyatake, K. Morimoto, J. -Y. Moon, M. Oyaizu, M. Rosenbusch, A. Taniguchi, and M. Wada, “Discovery of
new isotope 241 U and systematic high-precision atomic mass measurements of neutron-rich Pa-Pu nuclei produced via multinucleon
transfer reactions,” Phys. Rev. Lett. 130, 132502 (2023).
T. Niwase, W. Xian, M. Wada, M. Rosenbusch, S. Chen, A. Takamine, J. Liu, S. Iimura, D. Hou, S. Yan, H. Ishiyama, H. Miyatake,S. Nishimura, D. Kaji, K. Morimoto, Y. Hirayama, Y. X Watanabe, S. Kimura, P. Schury, and H. Wollnik, “Development of a β-TOF
detector: An enhancement of the α-TOF detector for use with β-decaying nuclides,” Prog. Theor. Exp. Phys. 2023, 031H01 (2023).
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RIKEN Accel. Prog. Rep. 56 (2023)

M. Rosenbusch, M. Wada, S. Chen, A. Takamine, S. Iimura, D. Hou, W. Xian, S. Yan, P. Schury, Y. Hirayama, Y. Ito, H. Ishiyama,
S. Kimura, T. Kojima, J. Lee, J. Liu, S. Michimasa, H. Miyatake, M. Mukai, J. Y. Moon, S. Nishimura, S. Naimi, T. Niwase, T. Sonoda,
Y. X. Watanabe, and H. Wollnik, “The new MRTOF mass spectrograph following the ZeroDegree spectrometer at RIKEN’s RIBF
facility,” Nucl. Instrum. Methods Phys. Res. A 1047, 167824 (2023).
S. Iimura, M. Rosenbusch, A. Takamine, Y. Tsunoda, M. Wada, S. Chen, D. S. Hou, W. Xian, H. Ishiyama, S. Yan, P. Schury, H. Crawford,
P. Doornenbal, Y. Hirayama, Y. Ito, S. Kimura, T. Koiwai, T. M. Kojima, H. Koura, J. Lee, J. Liu, S. Michimasa, H. Miyatake,J. Y. Moon, S. Naimi, S. Nishimura, T. Niwase, A. Odahara, T. Otsuka, S. Paschalis, M. Petri, N. Shimizu, T. Sonoda, D. Suzuki,
Y. X. Watanabe, K. Wimmer, and H. Wollnik, “Study of the N = 32 and N = 34 shell gap for Ti and V by the ﬁrst high-precisionmultireﬂection time-of-ﬂight mass measurements at BigRIPS-SLOWRI,” Phys. Rev. Lett. 130, 012501 (2023).

[Proceeding]
H. Sakai, H. Haba, K. Morimoto, and N. Sakamoto, “Facility upgrade for SHE research at RIKEN Nishina Center,” Acta Phys. Pol. B
Proc. Suppl. 16, 4-A10-1–12 (2023).

Presentations[International Conferences/Workshops]
H. Sakai (invited), “Facility upgrade for SHE research at RIKEN Nishina Center,” 57th Zakopane Conference on Nuclear Physics, Zakopane, Poland, August 28–September 4, 2022.
K. Morimoto (oral), “Present status and plans of GARIS-II and GARIS-III,” SSRI-PNS Collaboration Meeting 2022, Wako, Saitama &Online, September 1, 2022.
S. Kimura (oral), “Study of the neutron-rich 252 Cf-ﬁssion-fragments with MRTOF-MS,” The 16th International Symposium on Origin ofMatter and Evolution of Galaxies (OMEG16), Hanoi, Vietnam, October 24–28, 2022.
M. Tanaka (poster) and S. Sakaguchi for nSHE Collaboration, “Probing optimal energy for synthesis of element 119 from 51 V + 248 Cm
reaction,” The 28th International Nuclear Physics Conference (INPC 2022), South Africa, September 11–16, 2022.
P. Brionnet (invited), “Upgrade of the detection setup of the gas-ﬁlled recoil separator GARIS-III,” 19th TASCA22 Workshop, GSI
Darmstadt, Germany & Online, May 10–12, 2022.
P. Brionnet (poster), “Development and optimization of the digital electronic for the search of new super heavy element at RIKEN onGARIS-III,” 19th International Conference on Electromagnetic Isotope Separators and Related Topics, EMIS 2022, Daejeon, SouthKorea, October 3–7, 2022.

[Seminar]
H. Sakai, “Facility upgrade for SHE research at RIKEN Nishina Center,” C2R2 Seminer, IBS CENS, September 29, 2022.

[Domestic Conferences/Workshops]

倉本幸作 (ポスター発表), 森本幸司, 加治大哉, 武山美麗, 門叶冬樹, 「超重核実験用ピクセル型大面積半導体検出器の性能評価」,
第 37 回 研究会「放射線検出器とその応用」, 茨城県つくば市 (高エネルギー加速器研究機構放射線科学センター), 2023 年 1 月25–27 日.
倉本幸作 (ポスター発表), 森本幸司, 加治大哉, 武山美麗, 門叶冬樹, 「超重核実験用ピクセル型大面積半導体検出器の性能評価」, 第83 回応用物理学会秋季学術講演会, 東北大学川内北キャンパス & オンライン, 2022 年 9 月 20–23 日.
倉本幸作 (口頭発表), 森本幸司, 加治大哉, 武山美麗, 門叶冬樹, 「超重核実験用ピクセル型半導体検出器の不感層評価」, 第 59 回 ア
イソトープ・放射線研究発表会, オンライン, 2022 年 7 月 6–8 日.

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