III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Measurement of extraction time and eﬃciency of 220 Rn ions using acryogenic RF-carpet gas cell for the chemistry of superheavy elements
Y. Shigekawa,∗1 A. Yamaguchi,∗2 N. Sato,∗1 A. Takamine,∗1 M. Wada,∗3 and H. Haba∗1
We have been developing a cryogenic RF-carpet gas
cell for the gas-phase chemistry of superheavy elements(SHEs) with short half-lives (<5 s) such as 283 Cn (Z =112), 284 Nh (Z = 113), and 289 Fl (Z = 114).1) We
designed and constructed the gas cell, and measured
the transportation eﬃciency of ions from the surfaceof the RF carpet to its central hole (>80%) using Cs+ions emitted from a Cs ion source.1) In this work, wemeasured the extraction time and eﬃciency of ions to
the outlet of the quadrupole ion guide (QPIG) using
220
Rn (T1/2 = 55.6 s) ions emitted from a 224 Ra sourcewith recoil energy from alpha decay.
The 224 Ra source (45 kBq) was prepared by collecting 224 Ra ions recoiling out of a 228 Th source to thesurface of a Cu foil (diameter 10 mm).2) As shown in
Fig. 1, 220 Rn ions recoiling out of the 224 Ra source
placed 50 mm from the RF carpet were decelerated
by the He buﬀer gas, extracted from the RF carpet,
and transported to an Al foil (thickness 0.8 µm) via
QPIG. The number of 220 Rn ions on the Al foil wasmeasured by alpha-particle spectrometry using a Si detector. The extraction eﬃciency against a variety ofvoltages applied to the RF carpet and QPIG was obtained by dividing the number of 220 Rn ions extracted
on the Al foil by that emitted from the 224 Ra source.
The extraction time measurement was performed bysynchronously applying a pulsed voltage to the 224 Ra
source (55 V, width 2–10 ms) and a pulsed RF voltage
to the QPIG (1.6 MHz, 74 Vpp , width 2–100 ms). The
pulsed voltage to the source creates a pulse of 220 Rnions, which reach the QPIG with some delay. The
extraction time can be obtained by searching the pulseFig. 1. Setup of the measurement of extraction time andeﬃciency of 220 Rn ions.
∗1
∗2
∗3

RIKEN Nishina Center
Quantum Metrology Laboratory, RIKEN
Wako Nuclear Science Center (WNSC), IPNS, KEK

Fig. 2. Extraction eﬃciency of 220 Rn ions as a function ofthe RF voltage applied to the RF carpet.

Fig. 3. Counts of 220 Rn ions as a function of the pulse
RF voltage applied to the QPIG for a He pressure of
100 mbar (black circle). The diﬀerentiated data (redsquare) is ﬁtted with a Gaussian function (blue line).

width of the QPIG RF voltage at which the 220 Rncounts increase.
Figure 2 shows the extraction eﬃciency as a functionof the RF voltage applied to the RF carpet, where weﬁnd that the maximum eﬃciency is obtained with anRF voltage of 88 Vpp for every He gas pressure (50,100, 150, and 200 mbar, room temperature equivalent).
Similarly, we determined the best values for the audiofrequency voltage of the RF carpet, and the RF andDC voltages of the QPIG. We obtained an extraction
eﬃciency of ∼66% even for a He pressure of 200 mbar
(Fig. 2), which is higher than the value for the RFfunnel type gas cell (5% at 70 mbar).3)
Figure 3 shows an example of the results of the ex-- 145 -1

III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

traction time measurement, where the counts of 220 Rn
ions increase and saturate with an increase in the pulse
width of the QPIG RF voltage. The diﬀerentiateddata was ﬁtted with a Gaussian function, yielding amean extraction time of 22.0(6) ms for 100 mbar. The
mean extraction times for 50, 150, and 200 mbar were
determined in the same way as 6.7(4), 30.1(11), and33.8(9) ms, respectively.
The high extraction eﬃciency (∼66%) and fast extraction time (<40 ms) indicate that the developed gas
cell is applicable to the chemistry of SHEs with halflives of less than 100 ms at low production rates. We
plan to develop a gas chromatographic apparatus connected to the gas cell, and perform online experiments.
References

1) Y. Shigekawa et al., RIKEN Accel. Prog. Rep. 53, 168(2020).
2) Y. Shigekawa et al., Rev. Sci. Instrum. 87, 053508(2016).
3) C. Droese et al., Nucl. Instrum. Methods Phys. Res. B
338, 126 (2014).

2- 146 -