Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

The new MRTOF mass spectrograph following the ZeroDegree
spectrometer at RIKEN’s RIBF facility†

The newly assembled multi-reﬂection time-of-ﬂight
mass spectrograph (MRTOF-MS) at RIKEN’s RIBF
facility has been ﬁnalized and became fully operational
after its ﬁrst online operation in the spring of 2020.
Further modiﬁcations and performance tests using stable ions were completed in early 2021. This system
was coupled with a cryogenic helium-ﬁlled gas cell1)
located behind the ZeroDegree (ZD) spectrometer toslow down the high-energy reaction products from initially relativistic energies to thermal equilibrium withthe helium gas, and perform high-precision mass measurements of radioactive ions at low kinetic energies.
The setup underwent a successful commissioning2)
leading to ﬁrst important mass results recently published.3) Follow-up mass measurements were performed in dedicated beam times using the SRC accelerator4) (NP2012-RIBF 199/202).
A new optimization procedure for electrostatic mirror voltages has been implemented, which uses thepulsed-drift-tube technique to modify the ions’ energy
in a wide range and optimize the isochronicity of thesystem. The TOF could be made insensitive to thekinetic energy of the ions in a wide range. This procedure provided valuable initial settings of the mirrorvoltages, which have been used for further ﬁne tuning.
Figure 1 shows drift corrected TOF spectra obtained
after the full optimization, which show a mass resolving power of Rm ≈ 1 000 000. This result was reached
for a total time-of-ﬂight of only 12.5 ms for A ∼ 40,
which denotes a world record for such mass spectrometers. The new capabilities may allow for the study ofshort-lived nuclei possessing low-lying isomers.

normalized ion countM. Rosenbusch,∗1 M. Wada,∗1 S. Chen,∗2,∗3 A. Takamine,∗4 S. Iimura,∗1,∗4,∗5,∗6 D. S. Hou,∗7,∗8 W. Xian,∗2
S. Yan,∗9 P. Schury,∗1 Y. Hirayama,∗1 Y. Ito,∗10 H. Ishiyama,∗4 S. Kimura,∗4 T. M. Kojima,∗4 J. Lee,∗2J. Liu,∗2,∗7 S. Michimasa,∗11 H. Miyatake,∗1 J. Y. Moon,∗12 M. Mukai,∗4 S. Naimi,∗4 S. Nishimura,∗4T. Niwase,∗1 T. Sonoda,∗4 Y. X. Watanabe,∗1 and H. Wollnik∗14
1
0.8
0.6
0.4
0.2
01
0.8
0.6
0.4
0.2
036 Ar+

10.8
0.6
0.4
0.2
01
0.8
0.6
0.4
0.2
040 Ar+

10.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
084 Kr+a)

center T OF: 11954879 ns9204 events

4.98(19) ns

39 K+

center T OF: 12442853 ns71914 events

6.20(20) nsb)

center T OF: 12601321 ns73919 events

6.20(25) ns

39 K+

center T OF: 12442868 ns
67310 events

5.99(25) nsc)

center T OF: 18260868 ns1227 events

9.79(42) ns

85 Rb+

center T OF: 18369387 ns107885 events−15−1010.84(29) ns−50
T OF − center T OF [ns]510Fig. 1. Pairs of TOF spectra for one hour measurement
time (Ar/Kr from gas cell K/Rb and from a thermal
ion source). Numbers below double arrows: FWHM ofthe TOF signals.

Furthermore, a ﬁrst accuracy benchmark of thesetup was performed using isobaric species including
stable molecules and well-known radioactive ions fromBigRIPS. The mass deviations are shown with uncer-20†

50−5−1082 83 84 84 84 84 84 85 86 86 86 87 88 88 88 89 90 90 91 91−15r+
l2
1H12 C +e 1 Hl
77 S 2 C +1
le 1H
78 S 12 C +l2
e 1H
77 S 12 C +le 1H
76 S 2 C
1+e +l
76 S 16 O 4 37 C
2 5 Cl
12 C 3 4 +1 H F2
19212 C+H
14 7 Cl 212 C 3
1 H +l 2 +l5C
12 C 3 4 37 C
1 H
l5C
12 C 3+
1Hl+ 2 37 Cl
13 C
37 C l+5C+
12 C 3Cl
1 H 32 S 35
9F
12 C 1 H 4 1
4 16 O
12 C 2 +l2
1H35 C +12 C
1 H 7 Cl
313 C
l35 C+
12 C 1 Hr +83 K 1 H- 100 -1082 K+e82 S

Condensed from the article in Nucl. Instrum. Methods Phys.
Res. A 1047, 167824 (2023)∗1 Wako Nuclear Science Center (WNSC), IPNS, KEK∗2 Department of Physics, University of Hong Kong
∗3 School of Physics, University of York
∗4 RIKEN Nishina Center∗5 Department of Physics, Rikkyo University∗6 Department of Physics, Osaka University∗7 Institute of Modern Physics, Chinese Academy of Sciences∗8 School of Nuclear Science and Technology, Lanzhou University∗9 Institute of Mass Spectrometry and Atmospheric Environment, Jinan University∗10 Advanced Science Research Center, Japan Atomic EnergyAgency∗11 Center for Nuclear Study, University of Tokyo∗12 Institute for Basic Science∗13 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗14 New Mexico State University

MEExp. − MEAME2020 [keV]

15Fig. 2. Benchmark of the mass accuracy using well-known
species between A = 82 and A = 91.

Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 56 (2023)

tainties in Fig. 2. The precisely known masses of theanalyte ions could be reproduced with an overall mean
deviation of δm/m = 2.8(99) × 10−8 , which is a value
competitive with Penning-trap systems.
References
1) A. Takamine et al., RIKEN Accel. Prog. Rep. 52, 139(2019).
2) M. Rosenbusch et al., RIKEN Accel. Prog. Rep. 54, S28(2021).
3) S. Iimura et al., Phys. Rev. Lett. 130, 012501 (2023).
4) M. Rosenbusch et al., RIKEN Accel. Prog. Rep. 55, 86(2022).

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