III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Production cross sections of 225 Ac and 225 Ra in the 232 Th(14 N, xnyp)
reactions at 56, 79, and 98 MeV/nucleon
X. Yin,∗1 A. Nambu,∗1 S. Oshikiri,∗1,∗2 K. Suzuki,∗1,∗2 A. Hino,∗2 and H. Haba∗1
225Ac (T1/2 = 10.0 d) is one of the most promising alpha-particle-emitting radionuclides for targetedradionuclide therapy.1) Its precursor, 225 Ra (T1/2 =14.9 d), is useful to generate high-purity 225 Ac. Thus,
proton-induced reactions on 232 Th to form 225 Ac and225
Ra have been well investigated.2) Proton beams up to210 MeV are available for 225 Ac production from RRC.
In 1991, Ambe et al.3) proposed the productionof radionuclides of a large number of elements (multitracer) by the spallation of metallic targets suchas nat Cu, nat Ag, and 197 Au irradiated with a 135MeV/nucleon 14 N (or 12 C, 16 O) beam from RRC. With
this 14 N beam, 225 Ac and 225 Ra can be producedin the 232 Th(14 N, xnyp)225 Ac, 225 Ra reactions.4) Thecross sections are essential to verify the feasibility of
the 232 Th(14 N, xnyp)225 Ac, 225 Ra reactions for practical productions of 225 Ac and 225 Ra with RRC. Inour previous paper,4) we reported the cross sections of
the 232 Th(14 N, xnyp)225 Ac, 225 Ra reactions at 116 and132 MeV/nucleon. In this work, the cross sections atlower energies of 56, 79, and 98 MeV/nucleon were measured to evaluate the production yields of 225 Ac and225
Ra more reliably.
The target consisted of three assemblies of three metallic 232 Th foils, each with a thickness of 69 mg/cm2 andsize of 12.5 × 12.5 mm2 . Two aluminum disks, eachwith a thickness of 370 mg/cm2 and diameter of 15 mm,
were interleaved between the thorium assemblies as beamenergy degraders. The target was placed in a multitracer production chamber.5) A 100.1-MeV/nucleon
14 7+
N beam was extracted from RRC. The target wasirradiated for 2 h with an 18-particle nA intensity. After irradiation, the middle 232 Th foils in every assembly
were subjected to γ-ray spectrometry to determine thecross sections of 225 Ac and 225 Ra. The beam energies on
the measured 232 Th targets were calculated to be 98, 79,
and 56 MeV/nucleon using the stopping power model inthe LISE++ program.6) The cross sections of 225 Ac and225
Ra were determined by ﬁtting the 440-keV γ-ray intensity of 213 Bi (T1/2 = 45.59 min) in their radioactive
decay chain.4)
The cross sections of 225 Ac and 225 Ra obtained in thiswork are shown in Fig. 1, together with those at 116 and132 MeV/nucleon in our previous work.4) The cross sections of 225 Ac are larger than those of 225 Ra by factorsof 4.2–5.3 at 56–132 MeV/nucleon, respectively. The experimental results are compared with those calculatedby the Particle and Heavy Ion Transport code System(PHITS).7) The PHITS code reproduces the cross sec∗1∗2RIKEN Nishina Center
RI Research Department, FUJIFILM Toyama Chemical Co.,
Ltd.

Fig. 1. Experimental and calculated excitation functions forthe 232 Th(14 N, xnyp)225 Ac, 225 Ra reactions.

tions of 225 Ac above 98 MeV/nucleon, while it underestimates those at the lower energies. The cross sections
calculated for 225 Ra by the PHITS code are larger thanthe experimental ones. The calculated values increase
with the beam energy, while the experimental ones are
independent of the beam energy. In Fig. 2, production
yields of 225 Ac by 135-MeV/nucleon 14 N beams are compared with those by 210-MeV proton beams.2) The yields
of both reactions are comparable if we use a target withthe same thickness in the range of 0.5–5 g/cm2 .
By assuming experimental conditions (incident beamenergy: 132 MeV/nucleon; beam intensity: 1 particle
μA; target thickness: 4.5 g/cm2 ; irradiation time: 2 d),
165 MBq of 225 Ac can be produced at the end of bombardment via the 232 Th(14 N, xnyp)225 Ac reaction.

Fig. 2. Yields of 135-MeV/nucleon 14 N and 210-MeV proton
beams on 232 Th targets with diﬀerent thicknesses.

References
1) M. Ferrier et al., Radiochim. Acta 107, 1065 (2019).
2) J. Weidner et al., Appl. Radiat. Isot. 70, 2602 (2012).
3) S. Ambe et al., Anal. Sci. 7, 317 (1991).
4) X. Yin et al., RIKEN Accel. Prog. Rep. 54, 162 (2021).
5) H. Haba et al., Radiochim. Acta 93, 539 (2005).
6) O. B. Tarasov, D. Bazin, LISE++ site, https://lise.
nscl.msu.edu/lise.html .
7) Y. Iwamoto et al., J. Nucl. Sci. Technol. 54, 617 (2017).

- 147 -1