Ⅲ-3. Radiochemistry & Nuclear Chemistry
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Development of 211 Rn/211 At generator through liquid phase recoveryof radon and ionic liquid extraction of astatine
Y. Nagai,∗1 Y. Ganaha,∗1 A. Yokoyama,∗2,∗3 K. Washiyama,∗4 I. Nishinaka,∗5 X. Yin,∗3 A. Nambu,∗3Y. Shigekawa,∗3 and H. Haba∗3
The short path length and high linear energy transfer of α particles are expected to facilitate targetedalpha therapy for the treatment of tumor. A promising nuclide among various α emitters is 211 At with ahalf-life of 7.21 h, which has gained popularity owing
to its appropriate life and potential to synthesize labeled compounds as a halogen element. This has led
to several preclinical studies on At chemistry.1) To improve the availability of 211 At, a 211 Rn/211 At generator
was developed via the extraction using organic solventof DIPE or MIBK for expanding nuclide production
away from accelerator facilities because 211 Rn, which
has a half-life of 14.6 h, is the parent nuclide of 211 At.2)
In this study, we proved the wet chemistry processes
through liquid phase recovery of radon and ionic liquid
extraction of astatine for the generator.
In recent years, ionic liquids have attracted attention
as an alternative to organic solvents from the perspective of green chemistry. Ionic liquids exist in the liquid
phase at room temperature, have low volatility, andare ﬂame-retardant; therefore, the environmental loador risk of accidents is minimal. Further, the amountof radioactive waste can be reduced compared to thatusing organic solvents owing to their repeated usability. In addition, ionic liquids are considered promisingsolvents for extracting 211 At as per the reports on radiation resistance.3)
The nuclide of 211 At was produced via the209Bi(α, 2n) reaction at the RIKEN AVF cyclotron or
the decay of 211 Rn from the 209 Bi(7 Li, 5n) reaction at
the JAEA tandem Van de Graaﬀ accelerator. The irradiated Bi target was dissolved in 6 M HNO3 andﬁnally the 211 At nuclide was collected in dodecane solvent although the At species may diﬀer depending on
the procedures of preparation. The 211 At was further
extracted to 3 M HCl solution. Subsequently, 211 At
was extracted into an ionic liquid (IL) of [C8 mim]+[Tf2 N]− , where [C8 mim]+ and [Tf2 N]− are alkylimidazolium ion and bis (triﬂuoromethanesulfonyl) imideions, respectively. Finally, it was back-extracted into
0.1 M NaOH solutions. The α radioactivity of 211 At
was measured using a liquid scintillation counter to determine extraction rates of the nuclide for the relevant
∗1
∗2
∗3
∗4
∗5Graduate School of Natural Science and Technology,Kanazawa University
Institute of Science and Engineering, Kanazawa University
RIKEN Nishina Center
Fukushima Global Medical Science Center, Fukushima Medical University
Quantum Beam Science Research Directorate, National Institutes for Quantum Science and Technology- 149 -extraction procedures.
Figure 1 shows the extraction rates of 211 At fromdodecane into HCl solution, from HCl solution into IL,
and from IL into NaOH solution. Species in dodecane
were found to be dependent on the preparation of At as
observed upon the comparison of the results. Following
the extraction in HCl solution, At species appeared tobehave in a similar manner.

Fig. 1. Extraction rates for At from the decay of Rn (Rn→ At) and directly produced At (At).

Figure 2 shows the same extraction rates of 211 At
from the decay of 211 Rn, as in Fig. 1, but for withand without H2 O2 as a reductant. Reduction of At
species enhanced extraction into HCl and worked theother way in back-extraction with NaOH. This suggests that solvent extraction in practical applications
necessitates the adjustment of chemical species to havea good recovery of At.

Fig. 2. Extraction rates for At from the decay of Rn withand withou without H2 O2 .

References
1) F. Guérard et al., Cancer Biother. Radiopharm. 28, 1(2013).
2) E. Maeda et al., J. Radioanal. Nucl. Chem. 303, 1465
(2015).
3) L. Yuan et al., J. Phys. Chem. B 113, 8948 (2009).