Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 53

Separation and purification of 139 Ce tracer for metallofullerene synthesis
K. Akiyama,∗1,∗2 K. Amekura,∗1 and H. Haba∗2
Recently, clinical tests have been conducted on radionuclides of group 3 elements including lanthanides,
and some radionuclides were newly approved as radiopharmaceuticals. Metallofullerenes encapsulating lanthanide elements are attractive for application in electronic devices and pharmaceuticals. In particular, it isexpected that rich π electrons on a metallofullerene surface enable the production of various metallofullererene
derivatives by the addition of various functional groups
and that the encapsulation of radionuclides by thesederivatives could be applied as radiopharmaceuticals.
For such applications, excellent radionuclides, such as
139
Ce, emitting monochromatic γ rays and have a halflife of several months are required. In this paper, we
report the separation and puriﬁcation of a 139 Ce tracer
from its target material for metallofullerene synthesis.
Cerium-139 was produced from the 139 La(d, 2n)139 Cereaction using a nat La target irradiated with 5 µA of
24 MeV deuterons for 5 h at the RIKEN AVF cyclotron.
After the irradiation, the La target containig 139 Ce wasdissolved in nitric acid. For the separation and puriﬁcation of 139 Ce from La, the solvent extraction method wasemployed and was executed according to the procedureshown in the Fig. 1. The solution samples obtained in aseries of this extraction procedure were measured using a
Ge semiconductor detector to check the remaining 139 Ce
radioactivity in each sample.
The remaining amounts of the target material La andoxidant Cr were determined by optical absorption measurement and were found to be 2.1% and 3.9%, respec-Fig. 1. Schematic diagram of 139 Ce separation from a of Latarget.
∗1∗2

Department of Chemistry, Tokyo Metropolitan University
RIKEN Nishina Center

Fig. 2. HPLC elution behavior of 139 Ce metallofullerene
together with UV-monitored chromatogram of metallofullerenes produced in this study.

tively. The amount of remaining La in a single separation
process is still much larger than the amount of the 139 Cetracer. However, it has been found that by repeating
this separation procedure, it would be possible to obtaina suﬃciently puriﬁed 139 Ce tracer.
As mentioned above, the separated 139 Ce tracer still
includes large amounts of La and Cr. However, if theamounts of these impurities are suﬃciently small relative to that of the added carrier element and do notaﬀect the fullerene production, the purity of 139 Ce canbe said to be suﬃcient in this experiment. To conﬁrm
this, Tb4 O7 was added to a 139 Ce tracer solution, andthis solution was employed for the metallofullerene production under the same conditions as those previously
reported.1) In Fig. 2, the high-performance liquid chromatography (HPLC) elution behavior of 139 Ce metallofullerene (open circles) on a Buckyprep column (NacalaiTesque, Inc., eﬂuent: tolunene) is shown together with achromatogram aquired using UV absorption (gray solidline). The most dominant elution peak found in bothchromatograms are due to M@C82 .2) It is reported thatthe HPLC retention time of M@C82 on a buckyprep
column increases as the atomic number of the encapsulated lanthanide atom increased.3) The observed UVmonitored HPLC elution peak around 60 min occurs after that of Ce metallofullerene and is considered to be
derived from Tb@C82 because no HPLC elution peakwith suﬃcient intensity and faster retenton time thanthat of Ce@C82 is observed. In conclusion, the observed
elution peak is derived from Tb@C82 and the amount ofthe remaning La with this separation method is foundto be suﬃciently small.
References

1) K. Akiyama et al., RIKEN Accel. Prog. Rep. 49, 243 (2016).
2) H. Shinohara et al., Rep. Prog. Phys. 63, 843 (2000).
3) D. Fuchs et al., J. Phys. Chem. 100, 725 (1996).

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