II-9. Instrumentation

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Extraction test of photo ionized Bi in PALIS gas cellT. Sonoda,∗1 V. Sonnenschein,∗2 H. Tomita,∗2 K. Hattori,∗2 D. Hou,∗3 S. Iimura,∗3 H. Ishiyama,∗1 I. Katayama,∗1T. M. Kojima,∗1 S. Nishimura,∗1 M. Rosenbusch,∗3 A. Takamine,∗1 M. Wada,∗3 Y. X. Watanabe,∗3 and W. Xian∗3for the BigRIPS Collaboration
We are developing a scheme for parasitic low-energy
radioactive isotope(RI) beam production (PALIS)1) inthe second focal chamber (F2) of the BigRIPS.
Our previous experiment,2) conﬁrmed the extractionof Bi isotopes after exiting the PALIS gas cell. As thenext stage, we are aiming for laser photo ionizationof Bi, which results in highly pure RI beam production. Figure 1 shows the present PALIS experimental
setup. Bi atoms are irradiated by two colors of laser
beam for multi-step resonance ionization. Photo ionized Bi species are emitted as a gas jet into diﬀerential
pumping area, where the ions are conﬁned by rf electricﬁelds and move along an axial direction to the rf-carpet.
The rf-carpet makes superimposed electric ﬁelds: one isdc-guidance sloping to the small exit hole whereas, theother is rf-barrier that prevents the ions from hitting therf-carpet. For the fast evacuation, we utilized a large exit
aperture for the gas cell (3.0 mm) compared to that fora conventional gas cell. Owing to the small exit apertureof the rf-carpet (0.4 mm), eﬃcient diﬀerential pumping
can be realized, even though several small vacuum dry
pumps are arranged in the diﬀerential pumping area.
The extracted ions from the rf-carpet are detected byan ion counter in oﬀ-line experiments. In on-line beam
experiment, the ion counter is replaced by a silicon detector to observe the alpha rays created by the decay ofalpha-emitting Bi isotopes.
First, we examined the system performance by oﬀ-lineexperiments. Stable Bi atoms were produced in the gas
cell via evaporation. The applied laser ionization schemeof Bi is shown in Fig. 2(1). For identiﬁcation of Bi ionization, the ﬁrst-step laser wavelength was scanned as afunction of the ion intensity shown in Fig. 2(2). We also
conﬁrmed reasonable performance of the rf-carpet byscanning its rf-voltage, and the plot is shown in Fig. 2(3).
In November 2021, a 12-h on-line beam experiment
was conducted for the extraction test of 191 Bi. The setting B ρ at the BigRIPS provided the speciﬁc isotope
region including 191 Bi in the order of 105 cps. We moni-Ion count(cps)
Ion count(cps)’bi.dat’

(1).

(2).

SextuPole Ion Guide

Gas cellQuadruPole Ion Guide(3).

RF-Carpet RF(Vpp)
1st-step laser wavelength(nm)Fig. 2. (1): Bi-ionization scheme and number of ions per
second versus (2): ﬁrst-step wavelength, (3): rf voltage
at the rf-carpet measured in oﬀ-line experiment.

tored the alpha rays after implantation of a catcher platein front of the silicon detector, during the beam wasstopped for avoiding background noise. Figure 3 shows
the accumulated signals at the silicon detector. We considered that a few signals caused by alpha rays were observed in the expected area, >180 (MCA-ch) area. As
the extraction eﬃciency was not achieved for expectedvalue, some improvements are in progress.
alpha spectrum (counts)

60-s Beam ON 60-s Beam OFF x 5

1000

Signal of-decay

100

10

Expected signal area by -decay

10.1

Laser

83Bi

0100

200

300

400500600

MCA CHIon counting/
Alpha counting

Fig. 3. Observed signals at silicon detector in online experiment.
exit

differential pumping

rf-carpet(exit 0.4 mm)

photo ionized BiReferencesBi atom1) T. Sonoda et al., Prog. Theor. Exp. Phys. 113, D02(2019).
2) T. Sonoda et al., RIKEN Accel. Prog. Rep. 54, 91 (2020).

Fig. 1. Present experimental setup.
∗1
∗2
∗3

RIKEN Nishina Center
Faculty of Engineering, Nagoya University
Wako Nuclear Science Center, IPNS, KEK- 84 -1