Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 52 (2019)

Study of extraction yield of multi-nucleon transfer reaction products byusing cooled argon gas cellY. Hirayama,∗1 Y. X. Watanabe,∗1 M. Oyaizu,∗1 M. Ahmed,∗1,∗2 H. Choi,∗3 S. Iimura,∗4 H. Ishiyama,∗5
S. C. Jeong,∗6 Y. Kakiguchi,∗1 J. Y. Moon,∗6 M. Mukai,∗2 P. Schury,∗1 M. Wada,∗1 and H. Miyatake ∗1

∗1

∗2
∗3
∗4
∗5
∗6Wako Nuclear Science Center (WNSC), Institute of Particle
and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK)
Department of Physics, University of Tsukuba
Seoul National University
Osaka University
RIKEN Nishina Center
Institute for Basic Science, Rare Isotope Science Project136

Xe beamLaser
ionization+

Purified Ar gas~ 0.1 ppb

198

Pt rotating target
PT100+

gas jetLiq. N230 Pa

10 Pa

Doughnut-shaped
argon gas cellHe cryo module−4Fig. 1. Schematic view of the gas cell system with a coolingsystem. The details of the gas cell system were reportedin Ref. 2).
250

Counts200
150
1005030 kPa

00102015 kPa
30 kPa3040506070809060708090

Time (min.)
350Temperature (K)We have developed the KEK Isotope Separation
System (KISS) to study the β-decay properties ofneutron-rich isotopes with neutron numbers around N =126 for astrophysics research.1) KISS uses a laser ion
source to produce pure low-energy ion beams of theisotopes, which are produced as target-like-fragments(TLFs) in multi-nucleon transfer reactions by impinging
a stable 136 Xe beam with an energy of approximately
10 MeV/nucleon on a 198 Pt target. The extraction efﬁciency from the laser ion source, which is based on anargon gas cell, was as low as 0.1%.2) We assume thatthe low extraction eﬃciency stems from the formationof molecule ions between TLF ions and impurities in thegas cell. The molecule ions would be neutralized in theargon gas cell, and, therefore, we cannot conﬁrm the formation of neutral molecules by detecting and identifying
them using usual electromagnetic methods.
To study this assumption, we developed a cooling system for the argon gas cell to freeze out the impurities
in the argon gas and gas cell for suppressing the formation probability. Figure 1 shows a schematic view ofthe gas cell system with a cooling system that consistsof a He cryo-module and liquid nitrogen cooling circuit.
The gas cell is on the module to be cooled eﬀectively,
and liquid nitrogen is ﬂowed along a wall of the gas cell.
Two thermometers (Pt100) were installed to monitor thetemperatures at the center and the argon gas inlet partof the gas cell. The cooling system enabled the argon
gas and the gas cell to be cooled down to approximately
120 K in an oﬀ-line cooling test.
To study whether the extraction yield could be increased by suppressing the formation probability ofmolecules using the cooling system, we performed
an on-line experiment using a 136 Xe20+ beam with10.75 MeV/nucleon and an intensity of 20 pnA. Figure 2
shows the measured extraction yield of 198 Pt+ (top) andthe temperatures (bottom) as a function of time, respectively. The red and blue lines in the bottom ﬁgure show
the temperatures at the center and the gas inlet partof the gas cell, respectively. The extraction yield decreased with decrease in the temperature, and becamealmost saturated at 60 min with temperatures of 170 Kand 130 K at the center and the gas inlet part of thegas cell, respectively. The origin of bumps measured
at approximately 26 and 36 min in the top ﬁgure was

300
250
200
150
10050001020304050

Time (min.)Fig. 2. Measured extraction yield of 198 Pt+ (top) and thetemperatures (bottom) as a function of time.

unclear. After saturation, we decreased the argon gas
pressure down to 15 kPa from 30 kPa to keep the gas
density constant according to the change in temperature. After that, we found a recovery of the extraction
yield.
However, we did not ﬁnd any increase in the extraction yield by cooling the gas cell system. This indicates that the formation of molecules is not the dominant cause for the low extraction yield. The extraction
yield of unstable 199 Pt at 170 K was also the as same asthat measured at room temperature.
References

1) S. C. Jeong et al., KEK Report 2010-2, (2010).
2) Y. Hirayama et al., Nucl. Instrum. Methods Phys. Res. B
412, 11 (2017).

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