RIKEN Accel. Prog. Rep. 48 (2015)

Ⅲ-3. Radiochemistry & Nuclear Chemistry

Excitation function of the nat Hf(α,x)182g Ta reaction:
Cyclotron production of a long-lived γ-ray emitter 182g TaM. Murakami,∗1,∗2 H. Haba,∗1 and H. Kudo∗2∗1∗2

RIKEN Nishina Center
Department of Chemistry, Niigata University

obtained for the nat Hf(α,x)176,177,178 W, 178,183 Ta,Hf reactions, while cumulative ones were obtained for nat Hf(α,x)175,176,177,182g Ta, 175 Hf. The measured cross sections of the nat Hf(α,x)182g Ta reaction
are shown in Fig. 1 along with the calculated ones. Thecross sections in the energy range of 41–50 MeV were
measured for the first time. The excitation function
exhibits the maximum cross section of 8.3 ± 0.3 mb
at 41.5 ± 1.2 MeV. The data of Tárkányi et al.4) areconsistent with the present data at ≥30.7 MeV, whilethat at 27.6 ± 0.7 MeV (0.2 ± 0.3 mb) is much smaller
than the present one of 1.60 ± 0.08 mb at 27.2 ± 1.6
MeV. The cross sections calculated by the TALYS-1.6
code8) show systematically lower values with a similar
shape of the excitation function.
The physical thick-target yield was deduced from themeasured cross sections and the calculated stopping
power by the SRIM-2008 program.7) The deduced yieldof 182g Ta was 5.2 kBq/µAh at 50 MeV.
179m2,181

1010Cross
Cross section
section (mb)(mb)

We previously investigated the production of 179 Ta(T1/2 = 1.82 y) in the proton- and deuteron-induced
reactions on nat Hf1,2) for basic chemical studies ofthe 105th element Db, which must be conducted at asingle-atom scale. Although the long half-life of 179 Ta
is convenient for such the chemical experiments, thedecay characteristics of 179 Ta are less suitable: 179 Ta
does not emit any γ ray in its EC decay, and it mustbe traced by measuring the characteristic X rays ofHf, which are often interfared by X or γ rays of othernuclides.
Another long-lived Ta isotope, 182g Ta (T1/2 = 114.74d), is a γ-emitting isotope, and it has also been used asa radiotracer to explore the chemical behavior of Ta.
182g
Ta is usually produced by the 181 Ta(nth ,γ) reaction
with a high cross section of 20.5 ± 0.5 b.3) However, the182g
Ta radiotracer produced in this way is undesirable
for basic studies of Db, because it is obtained with amacro amount of the target material of Ta.
Very recently, Tárkányi et al. measured the crosssections of W, Ta, and Hf isotopes in the nat Hf(α,x)
reactions up to 40 MeV.4) As shown in Fig. 1,
they reported that the excitation function for thenatHf(α,x)182g Ta reaction increased with the beam energy. Because the 182g Ta tracer with high specific radioactivity can be obtained with this reaction, we further studied the production of 182g Ta in this reaction.
The excitation functions were measured by astacked-foil activation technique. 11 pairs of thinmetallic foils of nat Hf (97% chemical purity, 23 µmthickness) and nat Cu (99.9% chemical purity, 9 µmthickness) were stacked in an alternating sequence.
The nat Cu foils were used for monitoring the beam
current and energy by measuring the well-establishednatCu(α,x)67 Ga excitation function.5) The size of theall foils was 15 × 15 mm2 . The stack was bombarded
by a 50-MeV α beam supplied by the AVF cyclotronfor 31 min. The beam was collimated within 9 mm indiameter and the average beam current was 0.23 µA.
After the bombardment and the proper cooling duration, each foil was subjected to γ-ray spectrometry
with a Ge detector.
The production cross sections were derived by thewell-known activation formula.6) The beam energies
in the individual target foils were calculated with theSRIM-2008 program.7) The experimental cross sections were compared with the calculated ones by theTALYS-1.6 code.8)
In this work, independent cross sections were

182g
Hf(α,x)Hf(α,x)182gTaTanatnatThisThis workwork
Tarkanyi
Tarkanyi etet al.
al. (2014)(2014)TALYS-1.6
TALYS-1.6

861801804180180179179

20000

1010

Hf(α,pn)Hf(α,pn)Hf(α,d)Hf(α,d)Hf(α,p)Hf(α,p)202030
30

40
40

50
50

6060

α-particle
α-particle energy
energy (MeV)(MeV)

Fig. 1. Excitation function of the nat Hf(α,x)182g Ta reaction. Dashed curves indicate the individual reaction
channels evaluated by the TALYS-1.6 code.8)

References
1) M. Murakami et al.: Appl. Radiat. Isot. 90, 149 (2014).
2) M. Murakami et al.: RIKEN Accel. Prog. Rep. 47, 266
in(2014)press.
3) S. F. Mughabghab: in Atlas of neuteron resonances (Elsevier Science, 2006).
4) F. Tárkányi et al.: Appl. Radiat. Isot. 91, 114 (2014).
5) IAEA report IAEA-TECDOC-1211 (2007).
6) M. S. Uddin et al.: Nucl. Instrum. Methods Phys. Res.
B 258, 313 (2007).
7) J. F. Ziegler et al.: Nucl. Instrum. Methods Phys. Res.
B 268, 1818 (2010).
8) A. J. Koning et al.: in Proceedings of the International
Conference on Nuclear Data for Science and Technology, edited by O. Bersillon et al. (EDP Sciences, 2008),
p. 211.

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