RIKEN Accel. Prog. Rep. 50 (2017)

Ⅰ. HIGHLIGHTS OF THE YEAR

Commissioning of Rare RI Ring using exotic nuclei
D. Nagae,∗1 S. Omika,∗1,∗2 Y. Abe,∗1 Y. Yamaguchi,∗1 F. Suzaki,∗1 K. Wakayama,∗2 N. Tadano,∗2
R. Igosawa,∗2 K. Inokuma,∗2 Y. Arakawa,∗2 K. Nishimuro,∗2 T. Fujii,∗2 T. Mitsui,∗2 T. Yamaguchi,∗2T. Suzuki,∗2 S. Suzuki,∗3 T. Moriguchi,∗3 M. Amano,∗3 D. Kamioka,∗3 A. Ozawa,∗3 S. Naimi,∗1 Z. Ge,∗1,∗2Y. Yanagisawa,∗1 H. Suzuki,∗1 H. Baba,∗1 S. Michimasa,∗4 S. Ota,∗4 G. Lorusso,∗5 Yu.A. Litvinov,∗6M. Wakasugi,∗1 T. Uesaka,∗1 and Y. Yano∗1Fig. 1. T0,1 for each nuclei are deduced from the TOF
between S0 and the ring exit ELC. Figure 2 shows
the TOF spectra with peak assignments. Mass accuracies are preliminary obtained for 79 As, 77 Ga, 76 Zn,
and 75 Cu as 7.2 × 10−6 , 1.1 × 10−5 , 1.5 × 10−5 , and2.1 × 10−5 , respectively. The successful individual injection, storage, extraction, and TOF measurement in
the ring for exotic nuclei make the mass measurementof more neutron-rich nuclei feasible in the near future.

The Rare RI Ring1) is an isochronous storage ring
constructed to measure the masses of short-lived rare
nuclei using the time-of-ﬂight (TOF) measurement
method. We conducted two commissioning experiments2–4) in 2015. In the ﬁrst commissioning experiment, we veriﬁed the operation of each component, while in the second commissioning experiment,
we made the ﬁrst attempt of mass measurement using
stable nuclei. This year, we have performed commissioning using exotic nuclei with well-known masses toconﬁrm the feasibility and principle of mass determination using the following equation:

4800
79As

4600

78

Ge774400

Ga764200(1)

ΔE [ch]m 0 T1
m1=qq T0

1 − β12,1 − ( TT01 β1 )2

Zn
75

Cu

4000
3800

where m0,1 /q denote the mass-to-charge ratio of thereference particle and particle of interest, respectively;
T0,1 are revolution times of these particles; and β1 isthe velocity of the particle of interest. Because theisochronous condition is adjusted for the reference particle, isochronism is not fulﬁlled for particles of interestby the velocity measured upstream.
Exotic nuclei around 78 Ge were produced from therelativistic in-ﬂight ﬁssion of a primary beam of 238 U
at an energy of 345 MeV/nucleon on a 9 Be target witha thickness of 10 mm. We identiﬁed these nuclei before
the F3 achromatic focus of BigRIPS. Figure 1 showsa particle identiﬁcation plot. The energy loss (ΔE)
was obtained using an ionization chamber located at
F3, and TOF was measured between F2 and F3. Using Bρ and the measured TOF between F3 and the S0
achromatic focus of SHARAQ, the β1 values for particles were deduced. We injected these nuclei to thering using the individual injection method with the fastkicker system.5) The isochronous magnetic ﬁeld in thering was adjusted for the reference particle 78 Ge with a
precision of 5 ppm for a momentum spread of ± 0.3%.6)
We conﬁrmed the storage of several particles by using
a circulation detector7) and a δ-ray detector.8) These
particles circulated in the ring for about 1850 turns,
which corresponds to about 0.7 ms. Exotic nuclei 79 As,77−79
Ge, 76,77 Ga, 75,76 Zn, and 75 Cu were successfully
extracted from the ring as indicated by the red dot in∗1
∗2
∗3
∗4∗5
∗63600
3400
3200

50

5152

53

54

55

56

TOF (F2-F3) [ns]Fig. 1. Particle identiﬁcation plot. Green dots indicate all
events at F3, and red dots indicate extracted events.

10975

8Counts

79

676

54378

Cu775ZnZn

7776

Ge

As

Ge77

Ga

Ga79

Ge

2
101000

1100

1200

1300

1400

1500

1600

1700

TOF(S0-ELC) -700,000 [ns]Fig. 2. TOF spectra between S0 and ELC.

References
1) A. Ozawa et al., Prog. Theor. Exp. Phys. 2012, 03C009(2012).
2) Y. Yamaguchi et al., RIKEN Accel. Prog. Rep. 49, 18(2017).
3) Y. Abe et al., RIKEN Accel. Prog. Rep. 49, 19 (2017).
4) F. Suzaki et al., RIKEN Accel. Prog. Rep. 49, 179(2017).
5) H. Miura et al., RIKEN Accel. Prog. Rep. 49, 154(2017).
6) Y. Yamaguchi
Yamaguchi etet al.:al., In this report.
7) D. Nagae et al., RIKEN Accel. Prog. Rep. 49, 181(2017).
al., In this report.
8) S. Omika et al.:

RIKEN Nishina Center
Department of Physics, Saitama University
Institute of Physics, University of Tsukuba
Center for Nuclear Study, University of Tokyo
Department of Physics, University of Surrey
GSI Helmholtzzentrum für Schwerionenforschung- 18 -