Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 50 (2017)

Activation cross sections of α-induced reactions on nat Zn for 68 Geproduction
M. Aikawa,∗1,∗2 M. Saito,∗1,∗2 S. Ebata,∗1 Y. Komori,∗2 and H. Haba∗2∗1∗2Graduate School of Science, Hokkaido University
RIKEN Nishina Center- 257 -Table 1. Decay data of 68 Ge and 68 Ga
Nuclide6868

T1/2

Eγ (keV)Iγ (%)

Ge

270.95 d--Ga

67.71 min1077.34

3.22

nat250
Cross section (mb)Radioactive isotopes are used in nuclear medicinefor therapy and diagnosis. A positron emitter, 68 Ga(T1/2 = 67.71 min), is applied for positron emission
tomography (PET).1) In addition to 68 Ga, its longlived parent, 68 Ge (T1/2 = 270.95 d), is useful as a68
Ga generator.2) A possible reaction route to produce68
Ge (Z = 32) comprises alpha-induced reactions on
zinc isotopes (Z = 30), cross sections of which havebeen investigated previously.3,4) However, the amplitudes of the previous data are slightly diﬀerent fromeach other. We therefore measured cross sections ofthe alpha-induced reactions on natural zinc for 68 Ge
production.
The experiment was performed at the AVF cyclotronof the RIKEN RI Beam Factory by using the stacked
foil technique and the activation method. nat Zn foils(purity: 99.9%, Nilaco, Japan) were stacked with nat Ti
monitor foils (purity: 99.6%, Nilaco, Japan). The
thicknesses of the Zn and Ti foils were estimated fromthe measured area and weight of large foils (50 ×50 mm2 and 50 × 100 mm2 ) and found to be 18.64
mg/cm2 and 2.25 mg/cm2 , respectively. The stacked
target consisted of 14 sets of the Zn-Ti-Ti foils (8 × 8mm2 ) cut oﬀ from the large foils. The ﬁrst Ti monitorfoils at the downstream side of the beam were assumed
to compensate for losses of recoil products. The target
was irradiated for 2 h by a 51.5 MeV alpha beam withan average intensity of 41.0 pnA, which was measured
by a Faraday cup. The beam energy was measured
by the time-of-ﬂight method using a plastic scintillator monitor.5) The irradiated foils were subjected toγ-ray spectrometry by HPGe detectors.
The decay data6) are summarized in Table 1. The
measurement of the 1077.34 keV γ-line (3.22%) fromthe 68 Ga decay, which is in equilibrium with that of its
parent 68 Ge, was performed after a long cooling time ofabout 80 days. Each Zn foil with its Ti catcher foil wassimultaneously measured to collect the recoiled products. In the cooling time, all 68 Ga produced directly
through the nat Zn(α,x) reaction during the irradiation
could be considered to have decayed completely. The
cross sections derived from the measurement are shownin Fig. 1 together with the previous experimental data
(open squares and triangles)3,4) and the TENDL-2015
data (dashed line).7) The present result is slightly different from the previous experimental data, although
the peak position of approximately 30 MeV is consistent with them. In contrast, the TENDL-2015 dataZn(α,x)68Ge200

Haasbroek et al. 1976
Nagame et al. 1978
This work
TENDL2015

15010050001020304050

Energy (MeV)

Fig. 1. Excitation function of the nat Zn(α,x)68 Ge reaction.
The result is compared with the previous experimentaldata3,4) and TENDL-2015.7)

shows a diﬀerent tendency from the experimental data,probably because of underestimation of the contribution from the nat Zn(α,3n) reaction.
In summary, we performed an experiment on thealpha-induced reactions on natural zinc to produce
68
Ge, a generator of a positron emitter, 68 Ga. The
excitation function of the nat Zn(α,x)68 Ge reaction wasmeasured up to 51.5 MeV, and the peak position wasfound to be consistent with that of previous experiments.
References
1) S.R. Banerjee, M.G. Pomper, Appl. Radiat. Isot. 76, 1(2013).
2) F. Rösch, Appl. Radiat. Isot. 76, 24 (2013).
3) F.J. Haasbroek et al., CSIR Research Report, FIS 89(1976).
4) Y. Namage et al., Appl. Radiat. Isot. 29, 615 (1978).
5) T. Watanabe et al.: Proc. 5th Int. Part. Accel. Conf.
(IPAC2014), 3566 (2014).
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.