I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

First transport of unstable nuclei into SCRIT system
Y. Abe,∗1 T. Ohnishi,∗1 S. Ichikawa,∗1 A. Enokizono,∗1,∗2 R. Ogawara,∗1,∗3 K. Tsukada,∗1,∗3 H. Wauke,∗1,∗4M. Watanabe,∗1 and M. Wakasugi∗1,∗36Rate at 1W [atoms/s]

105137138139140141

Mass numberFig. 1. Isotope dependence of rate of Cs. Electron beampower is approximately 1 W. Total amount of uranium
is 28 g.
∗2
∗3∗44003002001000-100-1-0.5

00.5

11.5

2Time [ms]Fig. 2. Signal of 137 Cs beam at position monitor located at
entrance of SCRIT device.

References

4103

∗1500

The ERIS is almost ready for the world’s ﬁrst electron
scattering experiment with unstable nuclei, which will
be conducted in the future.

10101 W under the ionization chamber and target condition.
After adjusting the electric currents of the ionizationchamber and target heater to 150 A and 900 A, respectively, the rate of the RIs increased by approximately one
order, and we transported the 137 Cs beam to the SCRIT
system by monitoring it using Faraday cups in the beamline. To produce 137 Cs ions, an electron beam was irradiated was at a power of approximately 15 W. The produced 137 Cs ions were stacked in the ERIS with a 50 ms
stacking time. The pre-pulsed 137 Cs ions were injected
into the FRAC and subsequently stacked and extracted
from the FRAC as a pulsed beam in a cycle of 1 s. The
pulsed 137 Cs beam was successfully transported from theFRAC to the SCRIT system with approximately 100%transmission eﬃciency by carefully adjusting the optical parameters. Figure 2 shows the signal of the 137 Cs
beam at the position monitor located at entrance of theSCRIT device. The number of 137 Cs ions transported tothe SCRIT system was 9.8 × 106 atoms/pulse. The yieldof 137 Cs may be improved by optimizing the optical parameters from the ERIS to the FRAC and the stacking
conditions of the FRAC. It can also be increased by optimizing the temperature of the ionization chamber andthe target heater.

Voltage [mV]The electron-beam-driven RI separator for the SCRIT(ERIS)1) at the SCRIT electron scattering facility2) is an
online isotope separator system. It is used to produce
low-energy RI beams via photoﬁssion of uranium. Thisyear, we transported a pulsed 137 Cs beam, which wasproduced by a surface-ionization ion source and using
ion-stacking and pulse-extraction systems,3,4) into theSCRIT system. We report the results obtained from theexperiments.
Details of the RI production method and the surfaceionization ion source of the ERIS are reported in Refs. 4)
and 5). In the measurements, self-made 43 uranium carbide disks6) were used as production targets. The total
amount of uranium was approximately 28 g. We measured the production rate of Cs isotopes using a particle
identiﬁcation (PID) system1) located at the exit of theFRAC3) to estimate the rate of 137 Cs, because the lifeof 137 Cs is extremely long to measure γ-rays. In themeasurements, the electron beam power was adjusted toapproximately 1 W to reduce background events. The
target and the ionization chamber were heated to 1500–
2000◦ C by resistive heating. The electric currents applied to the ionization chamber and the target heater
were 120 A and 750 A, respectively. Ionized RIs wereextracted by the exit grid of the ionization chamber, accelerated to 10 keV, and transported to the PID system.
PID was performed by measuring speciﬁc γ-rays corresponding to the decay of the RIs using a Ge detector.
The measurement process is reported in Ref. 7). Figure 1 shows the isotope dependence of the rate of Cs
obtained from the experiments. The mass dependence issimilar to the trend reported from the ALTO8) , which isexpected to become ﬂat for masses lower than 139. From
this result, the rate of 137 Cs ion is estimated as approximately 1 × 105 atoms/s with an electron beam power ofRIKEN Nishina Center
Department of Physics, Rikkyo University
Institute for Chemical Research, Kyoto University
Research Center for Electron Photon Science, Tohoku University

1) T. Ohnishi et al., Nucl. Instrum. Methods Phys. Res. B
317, 357 (2013).
2) M. Wakasugi et al., Nucl. Instrum. Methods Phys. Res. B
317, 668 (2013).
3) M. Wakasugi et al., Rev. Sci. Instrum. 89, 095107 (2018).
4) T. Ohnishi et al., RIKEN Accel. Prog. Rep. 52, 142(2019).
5) T. Ohnishi et al., RIKEN Accel. Prog. Rep. 48, 229(2015).
6) T. Ohnishi et al., RIKEN Accel. Prog. Rep. 47, xiii (2014).
7) T. Ohnishi et al., RIKEN Accel. Prog. Rep. 53, 110(2020).
8) S. Essabaa et al., Nucl. Instrum. Methods Phys. Res. B
317, 218 (2013).

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