Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 53

On-line anion-exchange experiment of Nb and Ta in HF/HNO3 mixture
solution for Db chemistry
S. Adachi,∗1,∗2 A. Toyoshima,∗1,∗3 K. Tsukada,∗1,∗4 H. Haba,∗1 Y. Komori,∗1 T. Yokokita,∗1 Y. Shigekawa,∗1Y. Wang,∗1 A. Kashihara,∗1,∗2 M. Kato,∗1,∗5 A. Nakajima,∗1,∗5 and K. Sueki∗1,∗6
Superheavy elements with atomic number ≥ 104 areplaced at the 7th period of the periodic table. Owing
to the inﬂuence of strong relativistic eﬀects caused bytheir large positive nuclear charge, these elements are expected to have chemical properties diﬀerent from thoseof lighter homologues. However, because these elements
have very short half-lives and low production rates in nuclear reactions, it is diﬃcult to determine their chemicalproperties.
Few studies on the aqueous chemistry of Db, a group5 superheavy element, have been performed together
with the lighter homologues Nb and Ta and the pseudohomologue Pa. In the anion exchange in 13.9 M HF
solution, the distribution coeﬃcient (Kd ) of Db was reported to be smaller than those of Nb and Ta but larger
than that of Pa.1) In 0.31 M HF/0.1 M HNO3 solution, the adsorption of Db on the resin was showed tobe clearly weaker than that of Ta and similar to thoseof Nb and Pa.2) These studies suggest that Db wouldform [DbOF4 ]− like Nb or [PaOF5 ]2− and/or [PaF7 ]2−
like Pa, but not [DbF6 ]− like Ta. Thus, the purpose ofthe present study is to investigate whether Db behaves
like either Pa or Nb, particularly in high HF concentrations, which would enable us to deduce its chemical
form: [DbOF4 ]− or [DbF6 ]− . In this study, we performed on-line anion-exchange experiment of Nb and Ta
in HF/HNO3 mixture solution by using an automatedrapid chemistry apparatus (ARCA) to determine thesuitable experimental conditions for Db.
88g
Nb (T1/2 = 14.5 min) and 170 Ta (T1/2 = 6.7 min)were produced in the nat Ge(19 F, nx) and nat Gd(19 F, nx)
reactions, respectively, using the RIKEN K70 AVF
cyclotron. The reaction products transported by aHe/KCl gas-jet system were deposited on a collection

Fig. 1. Elution curves of 88g Nb and 170 Ta in 0.20, 11, 14.5 M
HF/1.0 M HNO3 solutions.
∗1∗2∗3∗4∗5∗6RIKEN Nishina Center
Graduated school of Pure and Applied Sciences, Tsukuba University
Institute for Radiation Sciences, Osaka University
JAEA Advanced Science Research Center
Science and Engneering, Tsukuba University
Faculty of Pure and Applied Sciences, Tsukuba University

Fig. 2. Variation of the distribution coeﬃcient, Kd , of Nb,
Ta, and Pa as a function of [F− ].

site of ARCA. Then, the products were dissolved in 0.1–
14.5 M HF/1.0 M HNO3 mixture solution. The solution
was fed onto a small chromatographic column (1.6 mmi.d. × 7 mm) ﬁlled with anion-exchange resin (MCI GELCA08Y) at a ﬂow rate of 1.0 mL/min. The eﬄuent fractions were collected in 7 polypropylene tubes. The products remaining in the column were stripped with 0.015 M
HF/6.0 M HNO3 mixed solution and were collected inanother PP tube. These fractions assayed by γ-ray spectrometry with a Ge detector to obtain elution curves forNb and Ta.
Figure 1 shows, the elution curves of 88g Nb and 170 Ta
in 0.20, 11, and 14.5 M HF/1.0 M HNO3 solutions.
The eluted radioactivity A(ν) at eﬄuent volume ν is expressed by the the{following equation: }(1)
A(ν) = Amax −N (νp − ν)2 /(2νp ν))
where Amax , N , and νp are maximum peak height, thenumber of theoretical plates, and the peak volume, respectively. The ν and νp values are corrected for thedead volume. The results of the ﬁt are in good agreement with the experimental data. The Kd value basedon the column chromatographic method is expressed asKd = νp /mr(2)where mr is the mass of dry resin. The average mr value
was measured to be 5.7±0.6 mg. The Kd values obtained
through the online column chromatography and a batchexperiment conducted separately are plotted in Fig. 2.
The Kd values in the on-line experiment are larger
than those in the batch experiment. However, the overall trend of Kd values, such as a sudden increase in theKd value of Nb at around [F− ]eq = 5 × 10−3 M, was reproduced. This suggests that the anion-exchange kinetics of Db may be fast in the present mixed solution, andthe Kd values of Db may be obtained under the present
conditions. In the near future, we will perform online
experiments of Db to determine its Kd value.
References

1) K. Tsukada et al., Radiochim. Acta 97, 83 (2009).
2) Y. Kasamatsu et al., Chem. Lett. 38, 1084 (2009).

- 162 -