II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Extraction test of stopped Bi isotopes in PALIS gas cellT. Sonoda,∗1 I. Katayama,∗1 M. Wada,∗2 H. Ishiyama,∗1 V. Sonnenschein,∗3 H. Tomita,∗3 R. Terabayashi,∗3K. Hattori,∗3 H. Iimura,∗4 S. Iimura,∗1 T. M. Kojima,∗1 M. Rosenbusch,∗2 A. Takamine,∗1 N. Fukuda,∗1T. Kubo,∗1 S. Nishimura,∗1 Y. Shimizu,∗1 T. Sumikama,∗1 H. Suzuki,∗1 H. Takeda,∗1 M. Tanigaki,∗5 andK. Yoshida∗1We are developing a scheme of parasitic low-energy
RI-beam production (PALIS)1) in the second focal
chamber (F2) of BigRIPS to eﬀectively use rare isotopes and to perform comprehensive measurements ofthe physical properties of exotic nuclei.
In our previous experiment,2) we conﬁrmed the feasibility of a new gas-cell geometry that separates high- andlow-radiation areas with a long gas tube. The current
setup for the PALIS on-line examination evaluates RI extraction by detecting alpha rays via alpha-emitter decay,
which results in enhanced sensitivity because of the extremely low background environment. While the alphaemitter element should be available on resonant laser
ionization in an oﬀ-line or on-line experiment. Therefore, we chose a bismuth (191 Bi) beam that can be produced by projectile fragmentation via a uranium beamand beryllium target. In a 12 hours online PALIS experiment, we focused on two objectives: 1) identify thestopped Bi isotope and 2) extract the stopped Bi isotope
from the gas cell.
To achieve the ﬁrst objective, we observed alpha rays
created via decays from the alpha emitters that werestopped in the ∆E solid-state detector (SSD) placedin front of the gas cell by adjusting the energy degrader, as shown in Fig. 1. As the energy resolution was considerably low because of the high electriCounts
20Counts
T1/2=11.87

0.73

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Fig. 1. Alpha spectrum observed using a ∆E Solid-state detector (SSD) placed in front of the gas cell. The inset
shows the alpha counts versus time in the beam-oﬀ period in the energy range of 6.1–6.6 MeV in the alphaspectrum.
∗1∗2
∗3
∗4
∗5RIKEN Nishina Center
Wako Nuclear Science Center (WNSC), IPNS, KEK
Faculty of Engineering, Nagoya University
Advanced Science Research Center, JAEA
Institute for Integrated Radiation and Nuclear Science, Kyoto
UniversityCounts
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ADC channelFig. 2. Alpha spectrum observed using a silicon PIN diodeplaced after the gas-cell exit.

cal background at F2, isotope identiﬁcation by alphaenergy (Eα ) was impossible from this energy spectrum.
However, we obtained other information from the timing chart by using a pulsed BigRIPS beam. The halflives extrapolated by decay ﬁtting to individual timing
charts for speciﬁc energy ranges were 42.12 ± 4.66 s (5.4–6.1 MeV), 11.87 ± 0.73 s (6.1–6.6 MeV) and 7.7 ± 0.3 s(6.6–7.5 MeV). The tentative isotope candidates forthese half-lives are 192 Bi (T1/2 = 39.6 s, Eα = 6060 keV),
191Bi (T1/2 = 12.4 s, Eα = 6309 keV), and 190 Bi (T1/2 =6.4 s, Eα = 6456 keV).
To achieve the second objective, we performed anextraction test of RIs that were stopped in argon gas(50 kPa) and transported to the gas-cell exit via a longgas tube by simple gas ﬂow to ﬁnally impinge on a silicon
PIN diode detector located after the gas-cell exit hole.
We conﬁrmed the extracted RIs from alpha spectra observed using the silicon PIN diode, as shown in Fig. 2.
These extracted RIs included species of all charge statessuch as neutral and positive/negative ions. By comparison with the total number of alpha counts detected
at the ∆E SSD, normalizing primary beam intensity,and considering the solid angle of the detector, we preliminarily evaluated the extraction eﬃciency as approximately 1%.
The extraction of stopped RIs out of the gas cell wasconﬁrmed. In the next beam time, we will apply laser
ionization for producing low-energy RI beam.
References

1) T. Sonoda et al., Prog. Theor. Exp. Phys. 2019, 113D02(2019).
2) T. Sonoda et al., RIKEN Accel. Prog. Rep. 53, 105 (2019).

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