III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Anion-exchange behavior of Db in HF/HNO3 solution
M. Kato,∗1 S. Adachi,∗2 A. Toyoshima,∗3 K. Tsukada,∗4 M. Asai,∗4 T. Yokokita,∗5 Y. Komori,∗5 Y. Wang,∗5Y. Shigekawa,∗5 D. Mori,∗5 H. Haba,∗5 A. Kashihara,∗2 A. Nakajima,∗2 K. Tokoi,∗6 Y. Suzuki,∗2 K. Nishizuka,∗2and K. Sueki∗7
The superheavy elements with atomic number ≥104
are located in the 7th period of the periodic table. Because of the relativistic eﬀects caused by the large positive charge of their atomic nuclei, they are expected tohave diﬀerent chemical properties from those of lighter
homologues. However, since these elements have very
short half-lives and low production rates, it is diﬃcult toreveal their chemical properties.
The aqueous chemistry of Db was studied in comparison with its lighter homologues Nb and Ta and thepseudohomologue Pa. Previous studies on the aqueous
chemistry of the ﬂuoride complex of Db suggested thatDb would form [DbOF4 ]− like Nb or [PaOF5 ]2− and/or[PaF7 ]2− like Pa, but not [DbF6 ]− like Ta.1,2) However,there was no signiﬁcant diﬀerence in the Kd values between Nb and Pa in the solutions in which Db anionexchange experiments were performed. Therefore, it was
not possible to determine whether Db was similar to Nbor Pa, and it is also diﬃcult to determine the chemical
species of the ﬂuoride complex of Db.
In our previous work, we revealed that there is a large
diﬀerence in the Kd values between Nb and Pa in themixture solution of HF and 1.0 M HNO3 .3) The diﬀerent
Kd values for Nb and Pa imply that they have diﬀerent
chemical species. Thus, it is considered that the chemical species of Db can be determined by obtaining the Kdvalue of Db in this mixed solution and comparing it withthose of Nb and Pa. In this study, we performed online
anion-exchange experiments of Db in HF/1.0 M HNO3
mixture solution using automated rapid chemistry apparatus (ARCA) to identify the chemical species of theﬂuoride complex of Db.
The online anion-exchange chromatography of 262 Db,88g
Nb, and 170 Ta was performed. The nuclides wereproduced in the 248 Cm(19 F, xn), nat Ge(19 F, nx), andnatGd(19 F, nx) reactions, respectively, at the RIKEN
K70 AVF cyclotron. In the 262 Db and 170 Ta experiments, the products were transported by the He/KClgas-jet system and were deposited on the collection siteof ARCA for 120 s. Subsequently, the products weredissolved in a solution of 14.5 M HF/1.0 M HNO3 . The
solution was fed onto the micro chromatographic column(1.6 mm i.d. × 7 mm) ﬁlled with anion-exchange resin(MCI GEL CA08Y) at a ﬂow rate of 1.0 mL/min. The
eﬄuent was collected on two Ta disks as fractions 1 and2. The remaining products in the column were strippedwith a solution of 0.015 M HF/6.0 M HNO3 and collected
on another two Ta disks as fractions 3 and 4.
∗1
∗2
∗3
∗4
∗5
∗6
∗7Master’s Program in Education, University of Tsukuba
Graduate School of Science and Tchnology, University ofTsukuba
Institute for Radiation Sciences, Osaka University
Japan Atomic Energy Agency
RIKEN Nishina Center
Graduate School of Science, Osaka University
Faculty of Pure and Applied Sciences, University of Tsukuba

Fig. 1. Distribution coeﬃcients, Kd , of Nb, Ta, Pa, and Db.

These disks were rapidly evaporated to dryness andsubjected to α-particle measurements with an automated rapid α/SF detection system.4) After the measurement, γ-rays of 170 Ta were monitored with Ge detectors.
In the 88g Nb and 170 Ta experiments, the transported
reaction products were deposited on the collection siteof ARCA and were dissolved in a solution of 4.4–14.5 M
HF/1.0 M HNO3 . Subsequently, the solution was fed
onto the microcolumn under the same experimental conditions as those for Db. The eﬄuent fractions were collected in 7 polypropylene(PP) tubes, and the remaining products were collected in another PP tube. Thesefractions were assayed by γ-ray spectrometry with a Ge
detector.
We conducted 350 anion-exchange experiments andobserved 5α events from 262 Db. Its adsorption probability on the resin was determined by the α counts found in
fractions 1–4. The Kd value of Db was determined using
the relation between Kd and the adsorption probability(%ads) of Nb and Ta studied in our previous work.3) Figure 1 shows the Kd values of Nb, Ta, Pa, and Db. The
Kd value of Db is close to that of Nb, while it is signiﬁcantly larger than that of Pa. In our previous study, we
found a large diﬀerence in the Kd value trends between
Nb and Pa. The increase in the Kd value of Nb indicates a change in the chemical species from [NbOF−
4 ] to[NbF−
6 ]. In contrast, the Kd value of Pa decreased monotonically, implying that the Pa species retains its form inthis [F− ] region. The present result suggests that Db issimilar to the behavior of Nb, and the chemical speciesof Db chage from ﬂuoro-oxo complex to ﬂuoride like Nb.
In the near future, we will perform further anionexchange experiments to observe the variation in Kd values of Db and identify the ﬂuoride complex of Db.
References

1) K. Tsukada et al., Radiochim. Acta, 97, 83 (2009).
2) Y. Kasamatsu et al., Chem Letts, 38, 1084 (2009).
3) S. Adachi et al., RIKEN Accel. Prog. Rep. 53, 162 (2020).
4) H. Haba et al., RIKEN Accel. Prog. Rep. 45, 204 (2012).

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