III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Production of 44 Ti via the 45 Sc(p, 2n)44 Ti reaction for 44 Ti/44g Sc
generator development
X. Yin,∗1 T. Fukuchi,∗2 Y. Watanabe,∗2 and H. Haba∗1
Table 1. Activities of 44 Ti, 44m, 46 Sc at EOB.

44g

Sc is a promising radionuclide for PET imaging applications.
Its direct production via the44Ca(p, n)44m, g Sc and 44 Ca(d, 2n)44m, g Sc reactions wereinvestigated by several groups.1–4) Owing to the shorthalf-life of 44g Sc (T1/2 = 3.9 h), daily irradiations close
to the site where it is used are required to maintaina constant supply of 44g Sc. An alternative approachto obtain 44g Sc is the production by the 44 Ti (T1/2 =59.1 y)/44g Sc generator.5) In this work, we investigatedthe production of 44 Ti via the 45 Sc(p, 2n)44 Ti reaction
to develop the 44 Ti/44g Sc generator.
A metallic 45 Sc (99.99%) disk target with a diameterand thickness of 10 mm and 0.90 g/cm2 , respectively,
was placed in an irradiation chamber with helium gasand water cooling.6) The target was irradiated for 1.25 hwith a 0.25-μA proton beam from the RIKEN AVF cyclotron. The incoming and outgoing proton beam energies were 30 MeV and 15 MeV, respectively.
Large amounts of 44m Sc (T1/2 = 58.6 h) and 44g Sc
were also produced in the 45 Sc(p, x)44m, g Sc reactions.
The short-lived 44g Sc fully decays in several days. Thus,
the activities of 44m Sc and 44 Ti at the end of bombardment (EOB) were determined by ﬁtting the decaycurve of the 1157-keV gamma line of 44g Sc after radioactive equilibrium. The yields of 44 Ti and 44m Sc withthe beam energy range of 30–15 MeV were calculated
based on the cross-section data reported by L. Daraban.7) The calculated results agree well with the experimental results. In addition, 46 Sc (T1/2 = 83.8 d) wasco-produced via the secondary-neutron-induced reactionof 45 Sc(n, γ)46 Sc. The activity of 46 Sc was determinedby the 889-keV and 1121-keV gamma lines after 76 daysof cooling. The results from the two gamma lines agree
well with each other and are listed in Table 1.
44Ti was separated from the target with ZR resin.
Firstly, the irradiated 45 Sc target (0.71 g) was dissolvedin 20 mL of 6 M HCl and heated to dryness. Subsequently, the residue was dissolved in 5 mL of 6 M HCland fed into a column ﬁlled with conditioned ZR resin(100–150 μm, 5 mm i.d. × 5 mm). Scandium passed
through the column while titanium was adsorbed on
the resin. Finally, 44 Ti was eluted with 6 mL of 3 M
HCl/0.325 M H2 O2 solution.8) The Ti/Sc separation factor was determined by the activity ratio of 44 Ti and 46 Sc
before and after separation. The recovery yield of 44 Ti
was 95%, and the Ti/Sc separation factor was >103 inthis scheme. The gamma-ray spectrum of 44 Ti after thechemical separation is shown in Fig. 1. Small amountsof long-lived 56 Co (T1/2 = 77.3 d) and 54 Mn (T1/2 =312.3 d) found in the irradiated target were successfully∗1∗2Fig. 1. Gamma-ray spectrum of 44 Ti after separation.

removed by the chemical separation. Only gamma lines
from 44 Ti and its daughter, 44g Sc, were identiﬁed in thegamma-ray spectrum. The radionnuclidic purity of 44 Ti
after chemical separation was evaluated to be >99%.
By assuming experimental conditions (incident beamenergy: 30 MeV; beam intensity: 10 μA; target thickness: 0.9 g/cm2 ; irradiation time: 10 d), 8 MBq of 44 Ti
can be produced at the EOB.
In the future, we will develop a prototype of the44Ti/44g Sc generator with long-term stability, high yieldof 44g Sc, and no 44 Ti breakthrough.
References
1) C. Alliot et al., Nucl. Med. Biol. 42, 524 (2015).
2) G. W. Severin et al., Appl. Radiat. Isot. 70, 1526 (2012).
3) C. Müller et al., J. Nucl. Med. 54, 2168 (2013).
4) R. Hernandez et al., Mol. Pharm. 11, 2954 (2014).
5) D. Filosofov et al., Radiochim. Acta 98, 149 (2010).
6) S. Yano et al., RIKEN Accel. Prog. Rep. 50, 261 (2017).
7) L. Daraban et al., Nucl. Instrum. Methods Phys. Res. B
267, 755 (2009).
8) V. Radchenko et al., J. Chromatogr. A 1477, 39 (2016).

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