Centers & Labs

RIKEN Nishina Center for Accelerator-Based Science

Rare RI-ring Team

Team Leader: Masanori Wakasugi (D.Sci.)
Masanori  Wakasugi(D.Sci.)

Mass measurement is one of the most important contribution to a nuclear property research especially for short-lived unstable nuclei far from the beta-stability line. In particular, a high-precision mass measurement for nuclei located around the r-process pass (rare-RI) is required in nucleosynthesis point of view. We chose a method of isochronous mass spectrometry (IMS) to make a measurement time shorter than 1 ms. Heavy-ion storage ring named "Rare-RI RIng (R3)" is now under construction at RIKEN RI Beam Factory. Our target performance in the mass determination is to achieve an accuracy of the order of 10^-6 (100 keV) even if we get only one event. Since an isochronism in R3 is established over a wide range of the momentum, rare-RIs with a large momentum spread, Δp/p=0.5 %, are acceptable. Another significant feature of the R3 system is an individual injection scheme in which a produced rare-RI itself triggers the injection kicker. Design study for R3 has been continued from more than ten years ago, and the construction has been started in 2012. In 2014, the construction was completed. We commissioned R3 in 2015 and 2016, and the performances of R3 has been evaluated. In commissioning experiments, we succeeded in determination masses for 79A, 77Ga, 76Zn, and 75Cu relative to a reference nucleus 78Ge. Since the current accuracy of the mass value is roughly 5 ppm, we are now improving the isochronism of R3. We have a plan to make mass measurements for 74-78Ni isotopes from 2017.

Main Research Field

Mathematical and physical sciences


  • Accelerator science
  • Nuclear physics
  • Electron scattering
  • Nuclear mass measurement

Selected Publications

  1. Y. Yamaguchi et al.:
    "Fast-kicker system for Rare-RI Ring"
    Phys. Scr. T166 (2015) 014056.
  2. Y. Abe et al.:
    "Isochronous field study of the Rare-RI Ring"
    Phys. Scr. T166 (2015) 014047.
  3. P. Shuai, et al.:
    "Charge and frequency resolved isochronous mass spectrometry and the mass of 51Co"
    Physics letter B 735 (2014) 327-331
  4. T. Yamaguchi et al.:
    "Performance of high-resolution position-sensitive detectors developed for storage-ring decay experiments"
    Nucl. Instrum. Methods Phys. Res. B 317 (2013) 697-700.
  5. F. Suzaki et al.:
    "Design study of a resonant Schottky pick-up for the Rare-RI Ring project"
    Nucl. Instrum. Methods Phys. Res. B 317 (2013) 636-639.
  6. D. Nagae et al.:
    "Time-of-flight detector applied to mass measurements in Rare-RI Ring"
    Nucl. Instrum. Methods Phys. Res. B 317 (2013) 640-643.
  7. Y, Yamaguchi et al.:
    "Construction of rare-RI ring at RIKEN RI Beam Factory"
    Nucl. Instrum. Methods Phys. Res. B 317 (2013) 629-635.
  8. T. Yamaguchi et al.:
    "The challenge of precision mass measurements of short-lived exotic nuclei: Development of a new storage-ring mass spectrometry"
    Int. J. Mass Spectrom. 349-350 (2013) 240-246.
  9. D. Shubina et al.:
    "Schottky mass measurements of heavy neutron-rich nuclides in the element range 70<=Z<=79 at the GSI Experimental Storage Ring"
    Phys. Rev. C 88 (2013) 024310/1-9.

Lab Members

Principal Investigator

Masanori Wakasugi
Team Leader

Core Members

Yoshiyuki Yanagisawa
Senior Research Scientist
Naohito Inabe
Senior Technical Scientist
Tamaki Watanabe
Senior Technical Scientist
Yutaka Watanabe
Senior Technical Scientist
Yoshitaka Yamaguchi
Nishina Center Research Scientist
Takeshi Maie
Nishina Center Technical Scientist
Yasushi Abe
Special Postdoctoral Researcher

Contact information

2-1 Hirosawa,
Wako, Saitama
351-0198, Japan

Email: wakasugi [at]

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