Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 51 (2018)

Activation cross sections of alpha-induced reactions on naturaltungsten for 186 Re and 188 Re production
N. Ukon,∗1,∗2 M. Aikawa,∗2,∗3 M. Saito,∗2,∗3 T. Murata,∗2,∗4 Y. Komori,∗2 H. Haba,∗2 and S. Takacs∗5Radioisotopes (RI) are used for diagnosis and therapy in nuclear medicine. 186 Re is a β emitter witha half-life of 3.72 days, a maximum β energy of
1.07 MeV, average penetration ranges of 1.1 mm insoft tissue and 0.5 mm in bone, and a 9.47% γ-rayemission at 137 keV. 188 Re is a β emitter with a halflife of 17 hours, maximum β energy of 2.12 MeV, and15.61% γ-ray emission at 155 keV.1,2) Both isotopes
can be used for theranostics (therapy and diagnosis).
We focused on a process to produce 186,188 Re
through alpha-induced reactions of natural tungsten
because we could ﬁnd data for only one 43 MeV.3)
Therefore, we measured the excitation function of thenatW(α, x)186,188 Re reactions up to 51 MeV.
The excitation functions of the nat W(α, x)186,188 Re
reaction were measured by the stacked-foil method,activation method and high-resolution γ-ray spectroscopy. nat W foils (purity: 99%, Goodfellow Co.,Ltd., UK) were stacked with nat Ti foils (purity: 99%,Goodfellow Co., Ltd., UK) for monitoring the beam
parameters and degrading the beam energy. The
thicknesses of the W and Ti foils were 15.03 and2.23 mg/cm2 , respectively.
The irradiation was performed at the RIKEN AVF
cyclotron. A 51 MeV alpha beam with an average intensity of 209.7 pnA was irradiated on the target for2 h. The incident beam energy was measured by thetime-of-ﬂight method using plastic scintillator monitors.4) The beam energy degraded in the stacked target
was calculated using the SRIM code available online.5)
The γ-ray spectra of the activated foils were measured
by an HPGe detector. Nuclear decay data were takenfrom the online NuDat 2.7 database.6)
From the net peak areas of the 137.16- and 155.04keV γ-rays, the activation cross sections for thenatW(α, x)186,188 Re reaction were deduced using thestandard activation formulaσ=Tγ λ−λtεd εγ εt Nt Nb (1 − e b )e−λtc (1 − e−λtm )

∗2
∗3
∗4
∗5

measurement dead time, which is the ratio of live time
to real time; λ the decay constant; tb the bombardingtime; tc the cooling time; and tm the acquisition time.
We found that our nat W(α, x)186 Re result is in good
agreement with previous data obtained by NE. Scott etal.3) and the theoretical calculation (TENDL-2015).7)
On the other hand, the nat W(α, x)188 Re result shows
disagreements with the other data. TENDL-20157)
underestimates the cross section at all energies.
Referenceswhere Nt denotes the surface density of target atoms;
Nb the number of bombarding particles per unit time;Tγ the number of counts in the photo-peak; εd thedetector eﬃciency; εγ the γ-ray abundances; εt the∗1Fig. 1. Excitation functions of the nat W(α, x)186,188 Re reactions. The result is compared with a previous study3)
and TENDL-2015.7)

Advanced Clinical Research Center, Fukushima Medical
University
RIKEN Nishina Center
Graduate School of Biomedical Science and Engineering,
Hokkaido University
School of Science, Hokkaido University
Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI)- 223 -1) A. M. Denis-Bacelar et al., Eur. J. Nucl. Med. Mol.
Imaging. 44, 620 (2017).
2) I. G. Finlay et al., Lancet Oncol. 6, 392 (2005).
3) N. E. Scott et al., Nucl. Phys. 119, 131 (1968).
4) T. Watanabe et al., Proc. 5th Int. Part. Accel. Conf.
(IPAC2014), (2014), 3566.
5) J. F. Ziegler et al., SRIM: the Stopping and Range ofIons in Matter, http://www.srim.org/.
6) National Nuclear Data Center: the NuDat 2 database,
http://www.nndc.bnl.gov/nudat2/.
7) A. J. Koning et al., TENDL-2015: TALYS-based evaluated nuclear data library.