Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 51 (2018)

Production of no-carrier-added barium tracer of 135m BaS. Yano,∗1 H. Haba,∗1 Y. Komori,∗1 T. Yokokita,∗1 and K. Takahashi∗1∗1CsCl (189 mg)
10 M HNO3 : 2 mL

×1

Heat to dryness
3 M HNO3 : 4 mL
3 M HNO3 : 2 mL
3 M HNO3 : 2 mL×30.01 M HNO3 : 2 mL
0.01 M HNO3 : 2 mL×3
Eichrom Sr resin column:
100-150 m; i.d. 7.5×H57 mm
Discard135mBaFig. 1. Chemical separation procedure of 135m Ba from theCsCl target.

㻝㻜㻢㻝㻜㻡Counts/0.5 keVThe long-lived 133 Ba isotope (half-life T1/2 = 10.51y) is the only Ba isotope commercially available fromJapan Radioisotope Association. Since 133 Ba is produced at a nuclear reactor, its specific radioactivity is
low with a typical value of approximately 0.5 MBqµg−1 .
Barium-135m with T1/2 = 28.7 h can be produced fromthe 133 Cs(α, x)135m Ba reaction by using a cyclotron.
Barium-135m emits a single 268.2-keV γ-ray, which
would be useful for radiotracer studies of Ba, especially for single- photon-emission computed tomography(SPECT).1) In this work, we investigated a procedure
to produce 135m Ba of high specific radioactivity by using the 133 Cs(α, x)135m Ba reaction and no-carrier-added
chemical separation.
CsCl powder (Sigma-Aldrich; chemical purity >99.999%) was pressed into a disk of 10-mm diameterand 240-mg cm−2 thickness at a pressure of 2 × 103 kg
cm−2 for 3 min. The CsCl pellet covered with a 10-µm
Al foil (chemical purity > 99.99%) was placed on a target holder. The target was irradiated for 30 min witha 50-MeV alpha beam having an intensity of 3.0 µA atthe RIKEN AVF cyclotron. During the beam irradiation, the target was cooled with circulating helium gas(30 L min−1 ) and water (1.5 L min−1 ). The beam axis
was continuously rotated in a circle of diameter approximately equal to 2 mm at 2 Hz to avoid local heatingof the target by using electromagnets on the beam lineof the RIKEN AVF cyclotron. After the irradiation,135m
Ba was chemically separated from the target material and by-products such as 135 La and 132 Cs by using a chromatography column filled with the EichromSr resin2) (Fig. 1). The radioactivity and radionuclidic
purity of the purified 135m Ba were determined by γ-ray
spectrometry using a Ge detector. The chemical purity and specific radioactivity were evaluated by chemical analysis using an inductively coupled plasma mass
spectrometer (ICP-MS). The γ-ray spectrum of the purified 135m Ba is shown in Fig. 2. Only Ba isotopes of131Ba, 133 Ba, 133 mBa, and 135m Ba were identified. The
radioactivity of 135m Ba was determined to be 2.25 MBqat the end of bombardment (EOB). The chemical yieldof 135m Ba was greater than 96%. Decontamination factors of 135 La and 132 Cs from 135m Ba were evaluatedto be 103 and 105, respectively. The radionuclidic
purity of 135m Ba was approximately 68% at the EOB.
The major radionuclidic impurity was 133 mBa (T1/2 =38.9 h) which was produced in the 133 Cs(α, x)133 mBareaction. Referring to the excitation functions for the133Cs(α, x)135m Ba and 133 Cs(α, x)133 mBa reactions inthe TENDL-2015 library,3) it is expected that the radionuclidic purity of 135m Ba can be increased at lower
beam energies. In the ICP-MS analysis, only Cu(1280 ng), U (160 ng), Zn (140 ng), and Ba (100 ng)

㻝㻜㻠㻝㻜㻟

511 keV :positron annihilation㻝㻜㻞: 135mBa: 133mBa: 133Ba: 131Ba

An elapsed time from the EOB : 15 h 57 min
Measurement time : 6111 s㻝

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㻜

㻡㻜㻜

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Energy/keVFig. 2. γ-ray spectrum of purified 135m Ba.

were detected among the elements having atomic number Z ≥ 20 in the purified 135m Ba with a contaminationlevel > 100 ng. The specific radioactivity of 135m Ba wasthen 23 MBq µg−1 at the EOB. This specific radioactivity is two orders of magnitude larger than that of thecommercial 133 Ba.
Based on the present results, we estimate that approximately 80 MBq of the no-carrier-added 135m Ba could be
produced after 24-h irradiation of the 240-mg cm−2 CsCltarget with the 50-MeV and 3-µA alpha beam. The expected specific radioactivity is approximately 830 MBqµg−1 .
References
1) R. P. Spencer et al., J. Nucl. Med. 12, 216 (1971).
2) E. P. Horwitz et al., Solvent Extr. Ion Exc. 10, 313 (1992).
3) A. J. Koning, D. Rockman, Nucl. Data Sheets 113, 2841
(2012).

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