Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Correlated measurement of mass and decay of fusion evaporation
products for 51 V+159 Tb reactions via MRTOF+α-TOF detector

The SHE-Mass-II facility1) is a system with a multireﬂection time-of-ﬂight mass spectrograph (MRTOFMS2) ) coupled with the gas-ﬁlled recoil ion separator
GARIS-II3) in the E6 experimental room for the massmeasurement of fusion evaporation products, such asvery low yield nuclei in the superheavy region.
Recently, we developed and installed a novel detector
named α-TOF4) , which simultaneously records the timeof-ﬂight (TOF) signal and successive α-decay. The αTOF detector has the capability to signiﬁcantly reducethe background level.
The experiment was performed using 51 V+159 Tbreactions.
A 51 V beam was accelerated up to6.0 MeV/nucleon by RRC. The beam energy on the target was reduced by an aluminum degrader to approximately 4.8 MeV/nucleon. A 460-µg/cm2 -thick 159 Tb
220

200180(a) Singles ToF

207Ra2+160
140120100

207Fr2+Counts / 3.2 ns8060yra40
20

2200

200180mile

160
140
120
1008060
40
200in

94.10594.10694.107(b) 207Ra gated ToF

pr94.10894.1096×10207Ra2+

694.105

94.10694.107

ToF [0.1 ns]

94.10894.109×10Fig. 1. (a) Singles TOF spectrum. (b) TOF spectrum incoincidence with 207 Ra α-decays obtained using a time
gate of 5s.
∗1∗2
∗3
∗4
∗5
∗6
∗7
∗8

∗9Department of Physics, Kyushu University
RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), KEK
Japan Atomic Energy Agency
Graduate School of Science and Engineering, Yamagata University
Department of Chemistry and Biochemistry, New Mexico
State University
Department of Nuclear Physics, The Australian National University
Department of Physics, Osaka University.
Institute for Basic Science

ToF [0.1ns]

T. Niwase,∗1,∗2,∗3 M. Wada,∗3 P. Schury,∗3 Y. Ito,∗4 S. Kimura,∗2 D. Kaji,∗2 M. Rosenbusch,∗2 Y. X. Watanabe,∗3Y. Hirayama,∗3 H. Miyatake,∗3 J. Y. Moon,∗9 H. Ishiyama,∗2 K. Morimoto,∗2 H. Haba,∗2 T. Tanaka,∗7S. Ishizawa,∗5,∗2,∗3 P. Brionnet,∗2 S. Iimura,∗8,∗2,∗3 A. Takamine,∗2 K. Morita,∗1,∗2 and H. Wollnik∗6inmilepryra

Energy [keV]

Fig. 2. Two-dimensional mapping of TOF versus correlated
α-decay energies.

target was prepared by a sputtering method on a 3.0 µm
Ti backing foil.
The fusion evaporation residues (ERs) were separated
from the primary beam and eﬃciently transported using GARIS-II. After decelerating ERs using a Mylar foil,
the ERs were captured in a cryogenic high-purity He gas
catcher, and the thermalized ions were extracted by an
RF-carpet and transported to the MRTOF-MS via multiple RF ion traps. We observed the 206, 207 Fr, 206, 207 Ra
and 204 Rn isotopes extracted as doubly charged ions.
In this measurement, we focused on 206, 207 Ra isotopes
having relatively short half-lives, i.e., T1/2 = 240 ms for206
Ra and T1/2 = 1.38 s for 207 Ra.
Figure 1 shows a part of the TOF spectrum at A =207. When we gated the ToF spectrum by the αray energy of 207 Ra with a coincident time of 5 s (3.5
half-lives), we clearly discriminated the decay-correlated
TOF events (Fig. 1(b)).
Figure 2 shows a part of the two-dimensional spectrum for TOF and the correlated α-decay energies. Fromthe correlation mapping, we obtained the informationof TOF, as well as decay properties such as α-energy
and decay time, atom by atom. Further analysis is inprogress.
References

1) M. Wada et al., RIKEN Accl. Prog. Rep. 52, 136 (2019).
2) P. Schury et al., Nucl. Instrum. Methods Phys. Res. B,335, 39 (2014).
3) D. Kaji et al., Nucl. Instrum. Methods Phys. Res. B, 317,311 (2013).
4) T. Niwase et al., Nucl. Instrum. Methods Phys. Res. A,953, 163198 (2020).

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