Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 51 (2018)

Cross section measurement to produce 99 Mo through alpha-induced
reactions on natural Zr
T. Murata,∗1,∗2 M. Aikawa,∗2,∗3 M. Saito,∗2,∗3 N. Ukon,∗2,∗4 Y. Komori,∗2 H. Haba,∗2 and S. Takács∗5
Radiopharmaceuticals containing 99m Tc (T1/2 =6.0 h) produced from the decay of 99 Mo (T1/2 = 66 h)
are used worldwide for imaging in diagnostic nuclear
medicine. Although nuclear reactors provide suﬃcient
global supplies of 99 Mo, unplanned shutdowns due totechnical issues disrupt these supplies. In addition,
the nuclear waste created by ﬁssion reactions in thenuclear reactors is a problem. Therefore, 99 Mo production routes other than neutron-induced ﬁssion areneeded.
One of the reactions that creates 99 Mo is the96Zr(α,n)99 Mo reaction. However, previously obtained
experimental cross section data1,2) and TALYS Evaluated Nuclear Data Library (TENDL)3) for this reaction exhibit discrepancies in their peak positions. Itis very important to provide reliable and consistentcross section data for evaluation of the isotope production yields. Therefore, we performed an experiment tomeasure the cross sections for this reaction.
The cross sections of the 96 Zr(α,n)99 Mo reaction
were measured using the standard stacked-foil activation method and oﬀ-line high-resolution high-purity
Germanium (HPGe) γ-ray spectrometry. Natural Zrfoils (purity: 99.2%, thickness: 20.3 µm; Nilaco Corp.,Japan) having 96 Zr isotopic abundance of 2.80% andnatural Ti foils (purity: 99.6%, thickness: 5.3 µm; Nilaco Corp., Japan) for the nat Ti(α,x)51 Cr monitor reaction were stacked together as a target. This stackedtarget was then mounted in a target holder that also
served as a Faraday cup, and irradiated by a 51-MeV
alpha beam with an average intensity of 203.6 pnA for
2 h at the RIKEN Azimuthally Varying Field (AVF)
cyclotron. The alpha particle energy in the i-th foil
Ei was derived using the stopping power calculated by
Stopping and Range of Ions in Matter (SRIM) software.4)
After a cooling time of 12 h to reduce the backgrounds, the γ-ray spectra on each foil were measured using high-resolution γ-ray spectrometry witha HPGe detector. The characteristic 739-keV γ-line(Iγ = 12.20%) from the decay of 99 Mo in the Zr foils
and the 320-keV γ-line (Iγ = 9.91%) from the decay of51
Cr in the Ti foils were measured to derive the crosssections of the 96 Zr(α,n)99 Mo and nat Ti(α,x)51 Cr re∗1
∗2
∗3
∗4
∗5Fig. 1. Experimental cross sections of 96 Zr(α,n)99 Mo reaction in comparison with previously reported experimental data and TENDL data.

actions, respectively. The distance between the measured foil and detector was optimized to maintain adead time lower than 10%. To obtain the production
cross sections of the assessed radionuclide σ(Ei ), thewell-known activation formula was used.
The measured production cross sections of 99 Mo areshown in Fig. 1, along with available previous data1,2)
and the TENDL data.3) Our result shows that the peakis located in the vicinity of 14 MeV with a cross section value of approximately 210 mb, diﬀering from theresults of earlier studies.
In this work, the cross sections of the 96 Zr(α,n)99 Moreaction were measured using standard methods, i.e.,the stacked target method, activation technique, andhigh-resolution γ-ray spectrometry. The newly measured cross section data were compared with previously
reported experimental data and the TENDL data. The
peak of the deduced excitation function was higher
than that given by the previous data and was locatedat approximately 14 MeV. To conﬁrm this excitation
function behavior, we will repeat this experiment indetail in the energy range of 10 to 20 MeV.
References1) D. P. Chowdhury et al., Nucl. Instrum. Methods B 103,261 (1995).
2) G. Pupillo et al., J. Radional. Nucl. Chem. 302, 911(2014).
3) A. J. Koning et al., Nucl. Data Sheets 113, 2841 (2012).
4) J. F. Ziegler et al., Nucl. Instrum. Methods B 268, 1818
(2010).

School of Science, Hokkaido University
RIKEN Nishina Center
Graduate School of Biomedical Science and Engineering,
Hokkaido University
Advanced Clinical Research Center, Fukushima Medical
University
Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI)- 25 -