Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

First confirmation of stopped RIs at parasitic gas cell with newapproach
T. Sonoda,∗1 I. Katayama,∗1 M. Wada,∗2 H. Iimura,∗3 V. Sonnenschein,∗4 S. Iimura,∗1 A. Takamine,∗1
M. Rosenbusch,∗2 T. M. Kojima,∗1 D. S. Ahn,∗1 N. Fukuda,∗1 T. Kubo,∗1 S. Nishimura,∗1 Y. Shimizu,∗1T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 M. Tanigaki,∗5 H. Tomita,∗4 K. Yoshida,∗1 and H. Ishiyama∗1
We are developing a scheme of parasitic low-energy
RI-beam production (PALIS)1) in the second focal
chamber (F2) of BigRIPS to establish the eﬀective utilization of rare isotopes and to perform comprehensive
measurements of the physical properties of exotic nuclei.
From previous experimental results,2) we ﬁgured outthat very intense radiation stays around the highenergy beam passage in F2. Under an intense radiation
environment, a strong plasma can easily be created inside the PALIS gas cell, which prevents the stopped RIs
from proper extraction. Therefore, we applied a new
approach to transport the stopped RIs from the strong
plasma via a long gas tube towards a lower-radiation
environment. This concept is similar to the “heliumjet” technique, but the present approach does not use
aerosols. In this beam time, we investigated the feasibility of this new approach by using alpha emitters produced by projectile fragmentation via a uranium beamand beryllium target.
Figure 1 shows a schematic of the experimental setup.

Fig. 1. Experimental setup.

SSD1
SSD2

Fig. 2. Alpha spectra observed by SSD1 and SSD2.

The gas cell is separated into two parts: a stoppingcell and an extraction cell which are joined with a70-cm-long and thin gas tube. High-energy alphaemitter beams were introduced to the stopping cell.
The BigRIPS optical parameters were set to those in
Sumikama et al.’s experiment.3) Firstly, we conﬁrmed
alpha rays created via decays from the alpha emittersthat were stopped in the delta-E SSD by adjusting theenergy degrader. By decreasing the degrader thickness,those observed alpha emitters were stopped inside thegas cell ﬁlled with argon gas at 0.5 to 1 atm. The alphaemitters stopped in the stopping cell were transported
to the extraction cell by a gas jet, where the radiation
intensity is at least 100 times lower than in the stopping cell. We observed a part of the alpha emittersthat were accidentally incident on the silicon pin-diode(SSD1) surface facing the ﬂow path at the entrance ofthe gas tube. Finally, we could conﬁrm the alpha emitters by inserting another silicon pin-diode (SSD2) in theﬂow path at the end of the gas tube. Figure 2 shows
the alpha spectra observed at SSD1 and SSD2.
The feasibility of the new gas cell structure was veriﬁed for the ﬁrst time. In the next beam time, we willevaluate the extraction eﬃciency and apply laser ionization for those alpha emitters.
References

∗1
∗2
∗3
∗4
∗5

RIKEN Nishina Center
High Energy Accelerator Research Organization, KEK
Japan Atomic Energy Agency, JAEA
Faculty of Engineering, Nagoya University, Nagoya
Institute for Integrated Radiation and Nuclear Science,KURNS

1) T. Sonoda et al., Prog. Theor. Exp. Phys. 2019, 113D02(2019).
2) T. Sonoda et al., RIKEN Accel. Prog. Rep. 51, 171 (2017).
3) T. Sumikama et al., Nucl. Instrum. Methods Phys. Res.
B 463, 237 (2020).

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