Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 53

Present status of 211 At production at the RIKEN AVF cyclotron
Y. Wang,∗1 N. Sato,∗1 Y. Komori,∗1 T. Yokokita,∗1 D. Mori,∗1 S. Usuda,∗1 and H. Haba∗1211

At is one of the most promising radionuclides fortargeted alpha radiotherapy owing to its suitable halflife of T1/2 = 7.214 h and high alpha-particle emission
probability of 100%.1) We have been producing 211 At
via the 209 Bi(α, 2n)211 At reaction at the RIKEN AVF
cyclotron.2,3) In this paper, we report improved production technologies of 211 At, which could reduce theseparation time from 2 h to 1 h and yield a neutral dry211
At product instead of the confused 211 At species inthe solution.
Figure 1 shows the production process for dry 211 At.
A metallic 209 Bi target (> 99.999%, 20 mg/cm2 ) wasprepared through vacuum evaporation on an Al plate(thickness: 1 mm). As shown in Fig. 1(a), the Bi target was placed at an angle of 15◦ with respect to thebeam axis. The target was cooled with water (10◦ C,1.5 L/min) and He gas (30 L/min) during the irradiation. An alpha beam with an energy of 29.0 ± 0.2 MeV
was delivered from the RIKEN AVF cyclotron. The
precise beam energy was measured using a time-offlight detector.4) A beam-wobbling system was used torotate the beam spot on the target and to prevent heatconcentration. After the beam passed through a Be
window (18.1 µm) and He cooling gas (65 mm, 1.1 bar),
the beam energy on the target was 28.0 ± 0.2 MeV,
as calculated with LISE (ver. 11.0.72). The beamintensity (4–32 µA) and irradiation time (2 to 8 h)
was varied to meet the users’ requirements. Subsequently, 211 At was separated from the Bi target byusing a dry distillation technique (see Fig. 1(b)). The
irradiated Bi target was placed on a copper tray in aquartz tube and heated up to 850◦ C in 10 min, following which it was kept for another 15 min and finallycooled down naturally. 211 At sublimated from the target was transported from the quartz tube through aquartz capillary (i.d. = 2 mm, length = 13 cm) to a
PFA cold trap (i.d. = 1 mm, length = 100 cm) by oxygen gas (10 mL/min). The PFA cold trap was cooled
to −96◦ C to collect the gaseous 211 At. As shown inFig. 1(c), after the distillation, the capillary and thePFA trap tube were washed with chloroform (FUJIFILM Wako Pure Chemical Corporation, Cat. No.:033-15721, Infinity Pure, 200–400 µL). The eluate collected in a 1-mL V-shaped glass vial was then dried
up by dry N2 gas (100 mL/min) at room temperature(see Fig. 1(d)). The chemical yields of the dry 211 At
products were determined by measuring the 687 keV γ-ray (Iγ = 0.261%) with a Ge detector. The chemical
purity of the products and the decontamination factor of 209 Bi from 211 At were evaluated with chemical
analysis using inductively coupled plasma mass spec∗1RIKEN Nishina Center- 192 -Fig. 1. Production process of dry 211 At.

trometry (ICP-MS).
We confirmed that the radioactivities of 211 At produced in the targets agreed well with those estimatedfrom thick target yields in the literature.5) The atomic
ratio 210 At/211 At was determined to be less than
2.1 × 10−6 at the end of bombardment (EOB), whichsatisfied the medical requirement of < 1 × 10−3 atEOB.4) The typical chemical yield was 80%. The
chemical impurities (> 1 ng) in 200 µL of chloroform
were Cu (43.84 ng), Al (38.90 ng), Zn (23.55 ng), andBi (6.70 ng). The decontamination factor of 209 Bi fordry 211 At was determined to be 8.3 × 10−8 .
By using the current production technology of 211 At,
1 GBq of 211 At can be produced through 1.5-h irradiation with a 32-µA alpha beam (27.8 MeV on target).
Dry 211 At can be prepared 4 h after EOB. We havebeen distributing 211 At to 14 users in Japan for theresearch and development of nuclear medicine.
References
1) M. Zalutsky et al., Curr. Radiopharm. 4, 177 (2011).
2) S. Yano et al., RIKEN Accel. Prog. Rep. 50, 263 (2017).
3) N. Sato et al., RIKEN Accel. Prog. Rep. 50, 262 (2017).
4) T. Watanabe et al., Proc. 12th Annual Meeting of Particle Accelerator Society of Japan, (2015), p. 1198.
5) A. Hermanne et al., Appl. Radiat. Isot. 63, 1 (2005).