Ⅲ-3. Radiochemistry & Nuclear Chemistry

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

Activation cross sections of 7 Li-induced reactions on nat Sm
M. Aikawa,∗1,∗2 G. Damdinsuren,∗3,∗2 S. Ebata,∗4,∗2 N. Ukon,∗5,∗2 and H. Haba∗2

∗1
∗2
∗3
∗4
∗5

Faculty of Science, Hokkaido University
RIKEN Nishina Center
Graduate School of Biomedical Science and Engineering,
Hokkaido University
Graduate School of Science and Engineering, Saitama University
Advanced Clinical Research Center, Fukushima Medical University

ferences in the γ line were assessed. The ground state(T1/2 = 13.517 y) and excited state of 152 Eu (T1/2 =9.3116 h) emit the same energy γ rays in the decay. The
long-lived 152g Eu decayed less during the measurements.
The contribution from 152m Eu (Iγ = 2.4%) could be neglected because no peak of the more intense γ line (Iγ= 14.2%) was found. Another possible interference ofthe 344.90-keV γ line (Iγ = 2.12%) from 151 Pm (T1/2 =28.40 h) was negligibly small because the more intense γline at 340.08 keV (Iγ = 22.5%) was missing in the spectra. The count rate of the 344.3-keV γ peak decreased
with the half-life of 152 Tb, indicating less contribution
from other radionuclides.
The result is shown in Fig. 1. No previous study of thereaction was found. According to the threshold energies(Table 1), the ﬁrst peak at 40 MeV comprises reactions
on several Sm isotopes. Above 60 MeV, the reaction
on 154 Sm can be dominant. We will ﬁnish analyses todetermine the cross sections of 152 Tb and other Tb radionuclides.
140

natSm(7Li,x)152Tb

120

Cross section (mb)Terbium radionuclides can be used for nuclearmedicine.1) High speciﬁc activities of the Tb radionuclides can be obtained using charged-particle-induced
reactions on neighbor elements, such as Gd, Er andSm. We focused on 7 Li-induced reactions on Sm. We
found two experimental studies for fusion reactions on
144, 152
Sm enriched targets in a literature survey.2,3) The
data shortage of the experimental cross sections motivated us to experiment with 7 Li-induced reactions onnat
Sm. Due to the isotopic ratio of nat Sm (144 Sm 3.08%,147
Sm 15.00%, 148 Sm 11.25%, 149 Sm 13.82%, 150 Sm
7.37%, 152 Sm 26.74% and 154 Sm 22.74%), the reactions
can produce Tb radionuclides simultaneously.
The experiment using a 7 Li beam was conducted atthe RIKEN AVF cyclotron. We adopted well-establishedmethods, such as stacked-foil activation technique and γray spectrometry, to determine activation cross sections.
Two nat Sm (5-µm thick, 99% purity, Nilaco Corp.,Japan) and one 27 Al (5-µm thick, >99% purity, Nilaco
Corp., Japan) foils were purchased for the stacked target. The size and weight of the foils were measured
to derive the average thicknesses. The measured thicknesses of the two nat Sm and 27 Al foils were 4.07, 4.20,
and 1.21 mg/cm2 , respectively. The foils were cut into asize of 10 × 10 mm. Nineteen sets of Sm-Sm-Al-Al foils
were stacked in a target holder that served as a Faraday
cup.
Irradiation with a 72-MeV 7 Li beam on the stacked
target lasted for 48 min. The incident beam energy wasmeasured using the time-of-ﬂight method. The beam energy degraded at each foil was calculated using the measured foil thicknesses and stopping powers retrieved fromthe SRIM code.4) The average beam intensity measured
using the Faraday cup was 48.9 nA.
The γ rays emitted from the irradiated foils were measured using a high-resolution HPGe detector (ORTEC
GMX30P4-70) and dedicated software (SEIKO EG&G
Gamma Studio). The γ-ray measurements of the nat Sm
foils were repeated ﬁve times with a cooling time of 1.1
h–2.7 d. The associated dead time was less than 2.2%.
The nuclear data required for the deduction of the crosssections were retrieved from NuDat 3.0.5)
The cross sections of the nat Sm(7 Li, x)152 Tb reaction were determined from net counts of the γ line at344.2785 keV (Iγ = 63.5%) emitted from the decay of152
Tb (T1/2 = 17.5 h). The spectra measured with thecooling time of 9.6–27.4 h were adopted. Possible inter-This work

100
8060
402000102030405060

70

Energy (MeV)

Fig. 1. Measured cross sections of the nat Sm(7 Li, x)152 Tb reaction.
Table 1. Q value and threshold energy (E th ) of the reaction
on each Sm isotope target for 152 Tb production.

Reaction
Sm(7Li,2n)152Tb
Sm(7Li,3n)152Tb
149
Sm(7Li,4n)152Tb
150
Sm(7Li,5n)152Tb
152
Sm(7Li,7n)152Tb
154
Sm(7Li,9n)152Tb
147
148

Q value
(MeV)
−5.7
−13.9
−19.8
−27.7
−41.6
−55.4

Eth (MeV)
6.0
14.5
20.7
29.1
43.6
58.1

References
1) C. Müller et al., J. Nucl. Med. 53, 1952 (2012).
2) P. K. Rath et al., Phys. Rev. C 88, 044617 (2013).
3) M. S. Gautam et al., Int. J. Mod. Phys. E 29, 2050029(2020).
4) J. F. Ziegler et al., Nucl. Instrum. Methods Phys. Res. B
268, 1818 (2010).
5) National Nuclear Data Center, The NuDat 3.0 database,
http://www.nndc.bnl.gov/nudat3/ .

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