Measurement of production cross sections of Tc isotopes in the natMo(d,x) reactions

Y. Komori,*1 M. Murakami,*1 and H. Haba*1

Chemical characterization of superheavy elements is one of the important and challenging subjects in the field of nuclear chemistry. We plan to conduct model experiments for chemical studies of element 107, Bh using radiotracers of its homologs, Tc and Re. Relatively long-lived isotopes, 95mTc (T1/2 = 61 d) and 184gRe (T1/2 = 35.4 d) are useful for tracer experiments. In the field of nuclear medicine, the isotope 99mTc, the daughter nuclide of 99Mo, is the most widely used for diagnostic imaging. Recently, the direct production of 99Mo/99mTc using an accelerator has attracted much attention. In this work, production cross sections of deuteron-induced nuclear reactions on natMo (nat: natural isotopic abundance) have been measured up to 24 MeV for the quantitative production of Tc isotopes. The results are discussed by referring to previously reported data and the theoretical model code TALYS.1)

The production cross sections were measured using a stacked-foil technique. Seventeen natMo foils (99.95% purity, 20.9 mg/cm2 thickness), sixteen natTi foils (99.5% purity, 9.2 mg/cm2 thickness), and sixteen natTa foils (99.95% purity,16.1 mg/cm2 thickness) were stacked in the order ofMo/Ti/Ta. The Ti foils were used to calibrate the beam current and the incident energy via the monitor reaction natTi(d,x)48V.2) The Ta foils were used to attenuate the beam energy. The size of all foils was 15 × 15 mm2. The target stack of the Mo/Ti/Ta foils was irradiated for 1 h with a 24-MeV deuteron beam supplied from the RIKEN AVF cyclotron. The average beam current was 0.17 μA. After the irradiation, each foil was subjected to γ-ray spectrometry with a Ge detector.

The excitation functions were measured for the natMo(d,x)93m,93g,94m,94g,95m,95g,96m,96g,97m,99mTc, 93m,99,101Mo, 90g,92m,95m,95g,96gNb, and 89gZr reactions. Figure 1 shows the excitation function of the natMo(d,x)95mTc reaction. Our results are in good agreement with the previously reported data.3‒5) It can be seen that the TALYS code (TENDL-2013) underestimates the cross sections at deuteron energies exceeding 10 MeV. For the other reactions, most of our results are in good agreement with those of previous studies. We measured the production cross section of 97mTc (T1/2 = 91 d) in the deuteron energy range of 14‒24 MeV for the first time. It was found that the TALYS code qualitatively reproduces the shape of these excitation functions, though there is little agreement between the experimental cross sections and the theoretical values. Thick-target yields for all the investigated Tc, Mo, Nb, and

Zr isotopes were deduced from the measured production cross sections. Figure 2 shows the thick-target yields of the Tc isotopes as a function of the deuteron energy. The deduced yield of 95mTc at 23.7 MeV is 0.36 MBq/µA·h. For 99Mo and 99mTc, the deduced yields at 23.7 MeV are 9.6 and

＊1 RIKEN Nishina Center

40 MBq/µA·h, respectively. To increase the production yields of 99Mo/99mTc and to reduce radioactivities from by-reaction products, the use of enriched 98Mo and 100Mo targets is favorable. Based on the present results, we will produce 95mTc for the model experiments on Bh chemistry. We will also develop a simple and efficient chemical separation scheme to obtain no-carrier-added Tc tracer from the Mo target.

References 1) A. J. Koning et al.: TENDL-2013: TALYS-based Evaluated

Nuclear Data Library, 2013. 2) IAEA: IAEA report IAEA-TECDOC-1211, 2007. 3) W. Sheng et al.: Inst. Nucl. Sci. Technol. Sichuan Univ. Rep.,

NST-004 (1990). 4) O. Lebeda et al.: Appl. Radiat. Isot. 68, 2425 (2010). 5) F. Tárkányi et al.: Nucl. Instrum. Meth. B 274, 1 (2012)

Fig. 1. The excitation function of the natMo(d,x)95mTc reaction.

0 10 20 300

10

20

30

40

50

60

70

Deuteron energy [MeV]

Cro

ss s

ectio

n [m

b]

natMo(d,x)95mTc This work Tarkanyi (2012) Lebeda (2010) Sheng (1990) Randa (1976) TENDL-2013

94Mo(d,n)

95Mo(d,2n)

96Mo(d,3n)

97Mo(d,4n)

Fig. 2. Thick-target yields of the Tc isotopes expressed as radioactivities after 1-h irradiation with 1 μA.

0 4 8 12 16 20 24 2810-4

10-3

10-2

10-1

100

101

102

103

Deuteron energy [MeV]

Thic

k-ta

rget

yie

ld [M

Bq/

A・

h]

93gTc

94mTc

93mTc

96mTc

94gTc

95gTc

96gTc

97mTc

95mTc

99mTc

Measurements of alpha-induced cross section for 48Cr and 49Cr up to

50 MeV

H. Kikunaga,∗1,∗2 M. Murakami,∗3,∗2 Y. Komori,∗2 and H. Haba∗2

Chromium is one of the essential trace elements insome animals but it also can be toxic in high concen-trations. Understanding the behavior of chromium inanimals, plants, and the environment is important andinfluential on the various fields such as biological sci-ences.The radioactive tracer technique has been widely

recognized as a powerful tool for behavior analysis ofelements in trace amounts. The isotopes 48Cr (T1/2

= 21.6 h), 49Cr (T1/2 = 42.3 m), and 51Cr (T1/2 =27.7 d) have potential as tracers because of their suit-able half-lives. In this work, the cross sections for thereactions natTi(α, X)48Cr and natTi(α, X)49Cr up to50 MeV were measured to produce these isotopes effi-ciently.The excitation functions of these reactions were mea-

sured by the stacked-foil technique. The target stackcontaining 20 natural Ti foils (99.5% pure) with thick-ness of 20 and 40 μm were irradiated with a α-particlebeam delivered from the RIKEN K70 AVF Cyclotronfor 30 min. The cyclotron was operated at a beam en-ergy of 50.4 MeV, which was confirmed by TOF mea-surement, with a mean current of around 0.4 μA.After the irradiation, the target foils were enclosed

in a polyethylene film separately and were subjectedto γ-ray spectrometry using a high-purity germaniumdetector. The incident beam energy and flux were de-termined by activation of the monitor foil techniqueusing the natTi(α, X)51Cr reaction. The reference datawere obtained from the IAEA Reference Data1). Theenergy loss in each foil was calculated using the TRIMcode2).

A γ-ray spectrum of a Ti foil sample at an effectiveenergy of around 50 MeV is shown in Fig. 1. The γ-peaks of scandium, vanadium, and chromium are ob-served in the spectrum. During the tracer preparation,it is necessary to separate chromium from titanium andthe other elements.The cross sections for the natTi(α, X)48Cr and

natTi(α, X)49Cr reaction obtained in this work areshown in Fig. 2. For comparison, the earlier experi-mental data3–6) of the natTi(α, X)48Cr reaction andthe values calculated using the Talys 1.6 code7) withdefault parameters are included in Fig. 1. The crosssections of 48Cr obtained in this work is in good agree-ment with the earlier experimental data. The calcu-

∗1 Research Center for Electron Photon Science, Tohoku Uni-versity

∗2 RIKEN Nishina Center∗3 Graduate School of Science and Technology, Niigata Univer-

sity

lated values with the Talys code reproduce the exper-imental values of 48Cr and 49Cr with a reasonable ac-curacy although each peak position of the excitationfunctions is deviated slightly.

Fig. 1. A γ-ray spectrum of a Ti foil sample at an effective

energy of around 50 MeV.

Fig. 2. Cross sections for the natTi(α, X)48Cr and natTi(α,

X)49Cr reactions.

References1) IAEA-Tecdoc-1211 2001 Charged particle cross section

database for medical radioisotope production: diagnos-tic radiosotopes and monitor reactions (IAEA, Vienna,2001).

2) J. F. Ziegler et al.: The stopping and range of ions insolids (Pergamon Press, New York, 1985).

3) R. Michel et al.: Radiochim. Acta 32, 173 (1983).4) R. Weinreich et al.: Appl. Radiat. Isot. 31, 223 (1980).5) A. Hermanne et al.: Nucl. Instrum. Meth. B 152, 187

(1999).6) X. Peng et al.: Nucl. Instrum. Meth. B 140, 9 (1998).7) A. J. Koning et al.: ”TALYS-1.0”, Proc.. Int. Conf.

Nucl. Data Sci. Technol. ND2007, Nice, France, 2007-04 (EDP Sciences, 2008) p.211.

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Ⅲ-3. Radiochemistry & Nuclear Chemistry RIKEN Accel. Prog. Rep. 48 (2015)RIKEN Accel. Prog. Rep. 48 (2015) Ⅲ-3. Radiochemistry & Nuclear Chemistry

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