Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 50 (2017)

Development of a production technology of 211At at the RIKEN AVF cyclotron:(ii) Purification of 211At by a dry distillation method
㻖4 䠆4
䠆1 㻖1
䠆1㻖1
䠆㻖1,2,3
1,2,3
1 1
1S. Yano,Sato,Toyoshima,
H. Haba,
Haba,䠆㻖1 Y. Komori,㻖䠆11S.S.Shibata,
K.K.Takahashi,
M.M.
MatsumotoS. Yano,N.N.Sato,
A.A.Toyoshima,
H.
Shibata,㻖䠆Takahashi㻖1䠆and, andMatsumoto䐦䐠䐤 䐥䐡䐟䐣䐢O2 gas䐨䐪Exhaust gas䐩Plungerpump(water)

䐧Cold trap

Fig. 1. Schematic of the dry distillation system of 211At.
ձ: KF40 flange with a heat sink for preheating of the O2 gas. ղ:O-ring. ճ: Quartz tube (28-mm i.d. × 200-mm length). մ:
Quartz spacer. յ: Bi target on an Al plate in Cu tray. ն: Quartz
capillary (2-mm i.d. × 130-mm length). շ: PFA connector. ո:
Electric furnace. չ: PFA trap tube (1-mm i.d. × 1-m length)cooled in a mixture of ethanol and dry ice. պ: PFA three-wayvalve. ջ: 1 M Na2S2O5 gas wash bottle. ռ: Charcoal gas washbottle.
2500

Counts / 3.18 keV211gPo : 7450.3 keV

(A)

2000

211At : 5869.5 keV

1500
1000
500
0
2000

4000

6000
Energy / keV

8000

610106105

211At / 211gPo(B)

Counts / 0.5 keVCounts / 0.5 keV

Astatine-211 is one of the promising radioisotopes fortargeted cancer therapy1) because 211At has a suitable halflife of T1/2 = 7.214 h for medical applications and a highĮ-particle emission probability of 100% in addition to its
short-lived decay daughter 211gPo (T1/2 = 516 ms). We havestarted to develop a production technology of 211At at theRIKEN RI Beam Factory to distribute this useful
radioisotope to the general public. In a separate paper,2) wehave reported the production technology of 211At from the209Bi(Į,2n)211At reaction using the AVF cyclotron. In thisreport, we describe a chemical purification procedure of211
At from the irradiated 209Bi target by a dry distillation
method. A schematic of the dry distillation apparatus isshown in Fig. 1. After the irradiation,2) the 209Bi target wasplaced on a copper tray in a quartz tube (28-mm i.d. ×200-mm length) and heated up to 850°C using an electric
furnace. 211At sublimated from the target material wasextracted from the quartz tube to a PFA tube (1-mm i.d. ×1-m length) through a quartz capillary (1.95-mm i.d. ×130-mm length) with O2 gas flow at a flow rate of 20 mL
min±1. The PFA tube was cooled at ±72°C in a mixture ofdry ice and ethanol to collect the gaseous 211At. Afterdistillation for 30 min at 850°C, the quartz capillary wasremoved from the quartz tube, and the inside of the quartzcapillary and the PFA trap tube were washed with 1 mL ofwater to recover 211At. The chemical yield of 211At wasdetermined by J-ray spectrometry using a Ge detector. The
radionuclidic purity was determined by Į-particle
spectrometry DQG Ȗ-ray spectrometry using Si and Ge
detectors, respectively.
The chemical purity and the decontamination factor of209
Bi from 211At were evaluated based on a chemical
analysis using ICP-MS. The Į-particle DQG Ȗ-ray spectra of
the purified 211At are shown in Figs. 2A and 2B,respectively. Only the peaks corresponding to 211At are
observed in the spectra. The chemical yield of 211At wasapproximately 60%; the major loss of 211At was due to thelow trap yield of the PFA tube. The radionuclidic purity of
the 211At solution was >99.9%, and the atomic ratio of210
At/211At was < 1.0×10±5 at the end of irradiation. Amongthe elements having atomic number Z 13 (Al), Cu (405ppb), Al (23 ppb), Tl (20 ppb), Bi (9 ppb), and Zn (8 ppb)
were detected with a concentration >5 ppb. The
decontamination factor of 209Bi from the purified 211At was3.0×10±7. We are ready to distribute 1 GBq of 211At for
researches in nuclear medicine.

104(76.9, 79.3, 89.6, and 92.4 keV)
410102103708090
Energy / keV100

210101
100

0500

1000
Energy / keV15002000)LJ  7\SLFDO $  Į-particle and (B) Ȗ-ray spectra of thepurified 211At obtained from a Bi target.
References

䠆1

RIKEN Nishina Center䠆2
Advanced Science Research Center, Japan Atomic Energy Agency
䠆3
Graduate School of Science, Osaka Univ.
䠆4Japan Radioisotope Association1) S. Huclier-Markai, Curr. Top. Med. Chem. 23(12), 1 (2012).
2) N. Sato et al., in this report.
3) K. Nagatsu et al., Appl. Radiat. Isot. 94, 363 (2014).

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