Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 52 (2019)

Preliminary analysis of the mass measurement experiment in thesouth-western region of 132 Sn with Rare RI Ring
H. F. Li,∗1,∗2,∗3 S. Naimi,∗1 D. Nagae,∗1 Y. Abe,∗1 F. Suzaki,∗1 Y. Yamaguchi,∗1 M. Wakasugi,∗1 S. Omika,∗4K. Inomata,∗4 H. Arakawa,∗4 S. Hosoi,∗4 K. Nishimuro,∗4 Y. Inada,∗4 T. Kobayashi,∗4 D. Kajiki,∗4
D. Hamakawa,∗4 W. B. Dou,∗4 T. Yamaguchi,∗4 M. Mukai,∗5 T. Moriguchi,∗5 R. Kagesawa,∗5 D. Kamioka,∗5A. Ozawa,∗5 S. Suzuki,∗2 Z. Ge,∗2 C. Y. Fu,∗2 Q. Wang,∗2 M. Wang,∗2 S. Ota,∗6 S. Michimasa,∗6 N. Kitamura,∗6S. Masuoka,∗6 D. S. Ahn,∗1 H. Suzuki,∗1 N. Fukuda,∗1 H. Takeda,∗1 Y. Shimizu,∗1 Y. A. Litvinov,∗7 G. Lorusso,∗8and T. Uesaka∗1
Mass measurement experiments were conducted atRare RI Ring (R3)1) in 2018. Neutron-rich 122 Rh,123, 124
Pd, and 125 Ag nuclides were measured in two set2)
tings. The principle of the mass masurement in the R3
can be described by the following equation:
�2
m1
m0 T1 �� 1 − β1=(1)
�()2
q1
q0 T0
1 − TT10 β1

where T1 and T0 are the revolution times of nucleus ofinterest and reference nucleus, respectively, and β 1 isthe velocity of the nucleus of interest.3) The unknown
mass m1 is determined relative to the mass of reference
nucleus m0 . When a particle is injected into R3 using thekicker magnet,1) it circulates for approximately 0.7 ms.
The particle is then extracted to ELC using the same
kicker magnet. The detector setup in R3 is shown inFig. 1 We measured the time-of-flight (TOF) from F3 toS0 to determine the velocities of each particle and from
S0 to ELC to determine T1 and T0 .
To obtain the revelotion time of the particle in R3, weneed to know the turn number of each particle before
the extraction. For this purpose, we used detectors atR-MD4 of R3, which were composed of the E-MCP detector,4) a plastic scintillator, and a CsI(Tl) telescope.
NaI (Beam stop)

Ion chamber
ELC PlaKicker Magnet

S0E-MCPE-MCPPla.
CsI(Tl) Tele.

Rare-RI Ring (R3)R-MD4

Fig. 1. Schemaic view of the detector setup at R3.
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8

Table 1. TOF, revolution times, and deduced turn numbersof nuclide in the two settings.
Nuclei

128

Rev. time [ns]394.00R3 TOF [ns]724922.66 724897.19 724904.61 724904.61

Turns

1840

127

Sn

391.69126In395.28127In

397.642
1823
125

Cd

399.04126

Cd

405.44
1806
124

Ag

402.99125Ag405.44
1788
123

Pd

407.09724293.23 724204.20 724284.13 724561.00 724621.441849

1832

1815

1798

1780

First, the telescope detectors and plastic scintillator atR-MD4 were placed on the central orbit and the injection time spectrum was recorded. Second, the detectors
were moved to the inner side of the ring, 85 mm awayfrom the central orbit, which corresponds to the extraction orbit. The TOF of the nuclei, circulating in R3, canbe determined from these two measurements. Third, weinserted the E-MCP detector with a thin foil into thecentral orbit of the ring to measure the revolution timeof the nuclei. The turn number of each nucleus wasdetermined based on the TOF obtained by the first twosteps and the revolution time obtained by the third step.
The TOF in the R3, revolution time measured by the EMCP detector, and the deduced turn number are listed
in Table 1. For 122 Rh and 124 Pd, the turn numbers could
not be clearly determined owing to the low statistics ofthe revolution times. However, the revolution times of122
Rh and 124 Pd could be precisely estimated based on
the mean Bρ value and central orbit length, which werecalibrated by the data of other nuclei.
To determine the mass, besides T0, 1 , we also need tocalculate β1 for each event. β1 will be determined by
the TOF between the F3 achromatic focus of BigRIPSand S0 and the corresponding path length that will becalibrated by the reference nuclei in the future.
References

RIKEN Nishina Center
Institute of Modern Physics, Chinese Academy of Sciences
University of Chinese Academy of Sciences
Department of Physics, Saitama University
Institute of Physics, University of Tsukuba
Center for Nuclear Study, University of Tokyo
GSI Helmholtzzentrum für Schwerionenforschung
NPL, University of SurreySn1) Y. Yamaguchi et al., Nucl. Instrum. Methods Phys. Res.
B 317, 629(2013).
2) S. Naimi et al., in this report.
3) A. Ozawa et al., Prog. Theor. Exp. Phys. 2012, 03C009 (2012).
4) Y. Abe et al., JPS Conf. Proc. 1, 013059 (2014).
5) D. Nagae et al., RIKEN Accel. Prog. Rep. 51, 168 (2018).

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