I. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Activation cross sections of proton-induced reactions onpraseodymium up to 30 MeV†
M. Aikawa,∗1,∗2,∗3 Y. Hanada,∗2,∗3 H. Huang,∗2,∗3 and H. Haba∗3

†
∗1
∗2
∗3

Condensed from the article in Nucl. Instrum. Methods Phys.
Res. B 508, 29 (2021)
Faculty of Science, Hokkaido University
Graduate School of Biomedical Science and Engineering,
Hokkaido University
RIKEN Nishina Center

2000
141Pr(p,2n)140NdCross section (mb)

The medical radionuclide 140 Nd (T1/2 = 3.37 d) is expected to be used as a 140 Nd/140 Pr in-vivo generator for
positron emission tomography (PET).1) It can be produced via charged-particle-induced reactions. Amongthe possible production reactions, we focused on theproton-induced reaction of 141 Pr. A survey revealed
three experimental studies of the reaction for 140 Nd production.2–4) However, the experimental cross sections in
the literature are largely scattered. Therefore, we performed an experiment to obtain the cross sections of the141
Pr(p, 2n)140 Nd reaction up to 30 MeV. The production cross sections of 141, 139m Nd and 139 Ce were also
determined.
We conducted an experiment using a 30-MeV proton
beam at the AVF cyclotron in RIKEN. We adopted thestacked-foil activation technique and high-resolution
gamma-ray spectrometry to determine the excitation
functions. The target consisted of pure metallic thinfoils of 141 Pr (99% purity), nat Ti (99.5% purity), and27
Al (>99% purity), which were purchased from Nilaco Corp., Japan. The nat Ti foil was used for thenatTi(p, x)48 V monitor reaction to assess beam parameters and target thicknesses. The 27 Al foil was interleaved to catch recoiled products. The side lengths andweight of each foil were measured to obtain the average thicknesses. The measured thicknesses of the two141
Pr, nat Ti and 27 Al foils were 68.6 and 68.5 mg/cm2 ,9.1 mg/cm2 , and 2.2 mg/cm2 , respectively. The large
foils were cut into small pieces of 8 × 8 mm2 to ﬁt atarget holder. Eighteen sets of the Pr-Al-Ti-Ti-Al foils
were stacked in the target holder, which served as aFaraday cup.
The stacked target was irradiated with a proton beamfor 15 min. The average intensity and primary energyof the beam were measured to be 201 nA and 30.2 MeV,respectively. Energy degradation in the stacked target
was calculated using stopping powers obtained from theSRIM code.5)
Gamma-ray spectrometry was performed using ahigh-purity germanium detector. Each 141 Pr foil wasmeasured together with the next 27 Al foil that caught
the recoiled products. The 141 Pr foils were measured
3–9 times to assess the decay curves of the products.
The cooling times were from 1.7 h to 31.9 d, and thedead time was maintained below 7.5%.
Cross sections of the nat Ti(p, x)48 V monitor reaction

Hogan (1971)
Zeisler (1999)
Hilgers (2005)
TENDL-2019
This work

1500

1000

500

05

1015

20

2530

Energy (MeV)

Fig. 1. Cross sections of the 141 Pr(p, 2n)140 Nd reaction withthe previous data2–4) and the TENDL-2019 values.7)

were derived for comparison with the IAEA recommended values.6) Based on the comparison, the thicknesses of the 141 Pr foils and the beam intensity werecorrected by +2% and −7% within the uncertainties.
The measured thicknesses of nat Ti and 27 Al were usedwithout any correction.
140
Nd has the ground state (T1/2 = 3.37 d) and themetastable state at 2.221 MeV (T1/2 = 0.60 ms). The
isomer fully decays to the ground state via the IT transition (IT: 100%). Because there are no measurable
gamma lines from 140 Nd, gamma rays with the decayof 140 Pr (T1/2 = 3.39 min) were instead measured under secular equilibrium with the decay of 140 Nd. Direct
production of 140 Pr during irradiation was negligiblebecause the cooling times were much longer than its
half-life. We measured the gamma line at 511 keV (Iγ= 102%) emitted from the irradiated foils, which weresandwiched between copper plates to force positron annihilation. The result is compared with those of theprevious studies2–4) and the TENDL-2019 values7) inFig. 1. Our excitation function is largely diﬀerent fromthose of the previous studies. The TENDL-2019 values slightly overestimate our experimental data below
23 MeV.
References1) S. K. Zeisler et al., Clin. Positron Imaging. 2, 324 (1999).
2) J. J. Hogan, J. Inorg. Nucl. Chem. 33, 3627 (1971).
3) S. K. Zeisler et al., J. Label. Compd. Radiopharm. 42,Suppl. 1, S921 (1999).
4) K. Hilgers et al., Radiochim. Acta 93, 553 (2005).
5) J. F. Ziegler et al., Nucl. Instrum. Methods Phys. Res.
B 268, 1818 (2010).
6) F. Tárkányi et al., IAEA-TECDOC-1211 (2007).
7) A. J. Koning et al., Nucl. Data Sheets 155, 1 (2019).

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