Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 51 (2018)

Direct mass measurement of a T1/2 = 10 ms nucleus with a relative
precision of 10−7 level
M. Wada,∗1,∗2 Y. Ito,∗2,∗8 P. Schury,∗1 S. Kimura,∗2,∗6 M. Rosenbusch,∗2 D. Kaji,∗2 K. Morimoto,∗2 H. Haba,∗2S. Ishizawa,∗2,∗4 A. Niwase,∗2,∗3 H. Miyatake,∗1 X. Y. Watanabe,∗1 H. Hirayama,∗1 J. Y. Moon,∗7 A. Takamine,∗2T. Tanaka,∗3,∗2 K. Morita,∗3,∗2 and H. Wollnik∗5Comprehensive mass measurement of all available nuclides is an important mission for nuclear physics, in particular for understanding astronomical nucleosynthesis.
So far masses of 2300 nuclei were experimentally determined with relative precisions of better than 1 ppm whileother 1000 nuclei were identified; however, the masses
are still unknown.1) The half-lives of those unmeasured
nuclei are distributed in a few orders of magnitude, but
dominantly in 10–100 ms range (Fig. 1).
In the past, there were no universal mass spectrometers suited for very short-lived nuclei having half-livesof ≈10 ms if a relative precision of 10−7 level is required. We developed a multi-reflection time-of-flight(MRTOF) mass spectrograph2) to cover the blanc zone
at the GARIS-II facility of RIBF. Fusion-evaporation
products were separated from the primary beam by thegas filled recoil ion separator and the energetic RI-beams
were then thermalized in a cryogenic gas cell. The thermal ions in the gas cell were extracted by a travelingwave rf carpet and accumulated in the two stages of atriplet rf ion trap system. The bunched ions in the trap
were provided to the MRTOF for time of flight measurements. The main purpose of this setup was to measure relatively long-lived trans uranium elements suchas Md or Es,3) so that the setting was not for quick

25Counts / 4 ns20WWTaHf Hf Hf Hf HfLuYb Yb Yb Yb YbYbTm
ErEr
Er Er ErErHo
DyDy
Dy Dy Dy Dy Dy
Tb
GdGd Gd GdGd
GdEu
Sm SmRePt
Ir
Os Os Os OsTlHg
Hg Hg Hg Hg Hg
AuPt Pt PtPtIr
Os1050-150Eu
SmSmTeSb
SnSn Sn Sn Sn Sn Sn SnIn
Cd Cd Cd
CdCdAgPdPdSn

RuKrKrBr
Se Se Se
As
GeGe GeGeGaSe

NiZnCuNi Ni Ni
CoFe Fe FeMn
Cr Cr CrV
Ti Ti Ti Ti Ti
Sc
Ca Ca CaCaKAr
Ni

GeGa
Zn Zn Zn
Cu
NiCdCdAg
Pd
Pd Pd PdRh
Ru Ru Ru Ru Ru
Ru

Nd Nd
Pr
CeCeCeLa
Ba Ba Ba Ba Ba
BaBa
Cs
Xe
Xe
Xe Xe Xe Xe XeI
Te Te TeSb
Sn
Sn

Mo MoMoMo MoMo
NbZr Zr ZrZrYSrSr Sr SrRb
Kr Kr KrKrBrSeHe HeH H

Li LiArClS S S
PSi Si SiAlMgMgMg
NaNe Ne NeFO O ON NC CB BBeCaKAr
ClS

Cooled ions in storage ringextraction and short trap sequence. The average transport time from GARIS-II to MRTOF was about 30 ms.
Even with this condition, we could measure the massof 219 Ra having a half-life of 10 ms with a precision of2×10−7 (Fig. 2).
Figure 3 shows correlations between the mass precisions and half-lives for various mass spectrometers.
Present 219 Ra measurement placed a milestone at theblanc zone.

-4-2-4-6-8log (T1/2)

Fig. 1. Half-lives of mass unknown nuclides (colored ones).
Gray boxes indicate masses known with better than
1 ppm precision but the light gray ones are indirectly
measured nuclides. Insert shows distribution of half-life
for mass unknown nuclides.
∗1
∗2
∗3
∗4
∗5
∗6

∗7
∗80.1 ppm

Fig. 3. Plot of mass precision as a function of the halflife with diﬀerent mass measurement devices. With theMRTOF ≈80 nuclides were measured in FY2016–17.3–6)

00

MRTOF ISOLDE
1 ppm

Half Life [s]c_unk1ppm2016_life.m

210 ppm

0.01 ppm

Penning Traps

BiPb Pb Pb
TlHg

4150

MRTOF RIKEN-KEK

T1/2: 10 ms - 100 ms

6100

219RaW

850

220Ra

Nd

colored:unknown

0ToF - 5471753 (ns)Isochronous storage ring

+4

gray:
mass known-50

In-ﬂight

log(T1/2)

FeCa

Nd Nd-100

Fig. 2. ToF spectrum for 219 Ra2+ ions. A mass precision of
2×10−7 was achieved with four sets of spectra.

YbTeN = 150 laps
rate ~ 0.04 cps
red- 2: 0.9(T1/2 = 10 ms)

15UPb

219Ra++

References

KEK, Wako Nuclear Science Center
RIKEN Nishina Center
Department of Physics, Kyushu University
Department of Physics, Yamagata University
Department of Chemistry and Biochemistry, New Mexico
State University
Department of Physics, Tsukuba University
Institute for Basic Science
Department of Physics, McGill University

1) W. J. Huang et al., Chinese Phys. C 41, 030002 (2017).
2) P. Schury et al., Nucl. Instrum. Methods B 335, 39(2014).
3) Y. Ito et al., Phys. Rev. Lett. 120, 152501 (2018).
4) P. Schury et al., Phys. Rev. C 95, 011305(R) (2017).
5) S. Kimura et al., Int. J. Mass Spectrom. 430, 134 (2018).
6) M. Rosenbusch et al., arXiv: 1801.02823.
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