Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Production yields of 165 Er and 169 Yb via 24-MeV deuteron inducedreactions
Y. Shigekawa,∗1 A. Nambu,∗1 Y. Kumakura,∗2 and H. Haba∗1
The use of Auger electrons for cancer therapy has
been widely investigated owing to their higher linear energy transfer than β − particles. 165 Er (T1/2= 10.4 h) and 169 Yb (T1/2 = 32.0 d), which decay
purely via electron capture (EC), are promising candidates for targeted radionuclide therapy using Augerelectrons.1,2) Moreover, the decay of 169 Yb accompanies the emission of cascade γ-rays potentially applicable to nuclear-medicine imaging that can prove
the local chemical environment.3) In order to perform
nuclear-medicine studies with 165 Er and 169 Yb, weneed to produce >1 GBq of 165 Er and >100 MBqof 169 Yb and chemically purify them without adding
carriers. The production cross sections for these isotopes were reported for the 165 Ho(d, 2n)165 Er4,5) and169Tm(d, 2n)169 Yb reactions.6–8) In this study, we conﬁrmed the production yields of 165 Er and 169 Yb via
24-MeV deuteron induced reactions using thick target
foils to determine the irradiation conditions to obtain
suﬃcient radioactivity for nuclear-medicine studies.
We irradiated 165 Ho and 169 Tm targets with a 23.9MeV deuteron beam at the RIKEN AVF cyclotron.
The 165 Ho target consisted of four 165 Ho foils (10 ×10 mm, 219.9 mg/cm2 , purity 99.9%) and was irradiated with an average beam intensity of 102 nA for30 min. The 169 Tm target consisted of nine 169 Tm foils(8 × 8 mm, 94.5 mg/cm2 , purity 99%) and was irradiated with an average beam intensity of 105 nA for 3h. After irradiation, γ-ray spectroscopy was performed
using high-purity Ge detectors.
The radioactivity of 169 Yb was determined with theγ peaks of 177.2 and 307.7 keV. For 165 Er, no-γ rays
are emitted; thus, the-X rays of Ho emitted after theEC decay were used to quantify 165 Er. The X-rays of
Ho (46.7, 47.5, 53.7, 53.9, and 55.3 keV) were observed
as three peaks in the γ-ray spectra. The peak corresponding to the 53.7- and 53.9-keV X-rays was useful to quantify 165 Er because the other X-rays overlap
with the Er X-rays emitted from 166 Ho (T1/2 = 26.8 h)
produced in the 165 Ho(d, p)166 Ho reaction. The countrate for the peak of the 53.7- and 53.9-keV X-rays wasobtained by ﬁtting a Gaussian function to each dataset.
The X-ray count rate as a function of the elapsed timedecreased with the half-life of 165 Er (10.4 h), meaningthat interference from radioactive impurities was negligibly small. To determine the radioactivity of 165 Er,
the self-absorption of X-rays by the thick Ho foils wascorrected using the γ-ray measurements for the twosides of each foil and a database of the X-ray absorp∗1∗2

RIKEN Nishina Center
Faculty of Medicine, Saitama Medical University- 176 -tion coeﬃcients.9)
The cross sections of 165 Er and 169 Yb (Figs. 1 and2) are almost consistent with those of previous studies.4–8) The total radioactivity of 165 Er at the endof bombardment (EOB) was 19.7(12) MBq, and theimpurity was 3.2(3) MBq of 166 Ho. The total radioactivity of 169 Yb at the EOB was 2.06(3) MBq,
and the impurities were 0.071(1) MBq of 168 Tm and0.16(3) MBq of 167 Tm. Hence, the thick target yields
for 165 Er and 169 Yb were determined to be 390(24)and 6.58(14) MBq/µAh, respectively. Via irradiation

Fig. 1. Excitation function of the 165 Ho(d, 2n)165 Er reaction measured in this work. The values measured inprevious studies4,5) are also shown for comparison.

Fig. 2. Excitation function of the 169 Tm(d, 2n)169 Yb reaction measured in this work. The values measured inprevious studies6–8) are also shown for comparison.

Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 56 (2023)

with a 5-µA deuteron beam, we will be able to produce
1 GBq of 165 Ho in 0.5 h and 100 MBq of 169 Yb in 3 h,which are suﬃcient for nuclear-medicine studies.
References
1) I. D. Silva et al., Molecules 26, 7513 (2021).
2) S. M. Qaim et al., Radiochim. Acta 95, 313 (2007).
3) K. Shimazoe et al., Commun. Phys. 5, 24 (2022).
4) F. Tarkanyi et al., Nucl. Instrum. Methods Phys. Res.
B 266, 3529 (2008).
5) A. Hermanne et al., Nucl. Instrum. Methods Phys. Res.
B 311, 102 (2013).
6) F. Tarkanyi et al., Appl. Radiat. Isot. 65, 663 (2007).
7) A. Hermanne et al., Nucl. Instrum. Methods Phys. Res.
B 267, 727 (2009).
8) M. Saito et al., Appl. Radiat. Isot. 125, 23 (2017).
9) M. J. Berger et al., XCOM: Photon Cross Section
Database (version 1.5), National Institute of Standards
and Technology, Gaithersburg, MD (2010).

2- 177 -