Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 53

Anion exchange of Zr, Hf, and Th by the automated extraction
apparatus: toward the chemical study of 104 Rf in HNO3
E. Watanabe,∗1 T. Yokokita,∗2 Y. Kasamatsu,∗1 S. Hayami,∗1 K. Tonai,∗1 Y. Shigekawa,∗2 H. Haba,∗2 andA. Shinohara∗1
Chemical elements with Z ≥ 104 are called superheavy elements (SHEs). The chemical properties ofSHEs are almost unknown because they must be synthesized by heavy-ion-induced nuclear reactions using
accelerators with very low cross sections and have very
short half-lives (T1/2 ≤ 1 min). There are some chemical
experiments on 104 Rf in solution chemistry; however, its
chemical properties are not suﬃciently understood due
to limited experimental methods. Further systematic experimental studies are needed. In our previous work, wedeveloped the automated batch-type solid-liquid extraction apparatus (AMBER) and investigated the anionexchange behavior of Rf in HCl and H2 SO4 to obtain
the distribution coeﬃcients (Kd ) of Rf under chemical
equilibrium conditions.1,2)
In this study, we focus on the formation of the Rf nitrate complexes. Indeed, the clear diﬀerence between
the complexation of Th (pseudo homologue of Rf) andthose of Zr and Hf (homologues) in HNO3 is known; Thforms an anionic complex with large coordination numbers of 10 and/or 12, while Zr and Hf do not. We previously found that anion-exchange reactions using Adogen464 resin (anion exchanger) in HNO3 reach the chemical
equilibrium in 60 s for Th, and this resin is promisingfor 261 Rf (T1/2 = 68 s) experiments. Toward the anionexchange experiments of Rf in HNO3 using AMBER,herein, we determined the experimental conditions forwashing the resin and its repetitive use.
We produced the 88 Zr and 175 Hf isotopes in the89Y(d, 3n) and nat Lu(d, xn) reactions, respectively, byusing the RIKEN AVF cyclotron. 234 Th was separated
from 238 U (α-decay mother nuclide). These radionuclides were puriﬁed by an anion-exchange method.
0.3 mL of 8 M HNO3 including 88 Zr, 175 Hf, and 234 Th
was injected into the chemical reaction container in AMBER, containing 3 mg of the Adogen 464 resin, and thecontainer was shaken for 60 s (anion-exchange part). After only the solution phase was discharged from the container passing through a PTFE ﬁlter with compressed
air, the Zr, Hf, and Th adsorbed on the resin were
washed out by injecting 0.1 M HNO3 or 0.1 M HCl into
the container (back extraction part). In the same manner as above, the washing solution was discharged fromthe container. This part was repeated until all of Zr, Hf,and Th were excluded from the resin. The recovery rateuntil the m-th back extraction was determined from thefollowing equation:
R(m) =m∑i∗1∗2Ai /n∑Ai ,iGraduate school of Science, Osaka University
RIKEN Nishina CenterFig. 1. Recovery rate R(m) of Zr, Hf, and Th using 0.1 M
HNO3 and 0.1 M HCl as the back extractant.

where Ai is the radioactivity of the solution in the ith back extraction, and n is the total number of backextraction.
Figure 1 shows the behavior of R(m) as a function ofm. This graph shows that 9 or 10 times of back extractions are required to wash out all of the Zr, Hf, and Th
adsorbed on the resin in 0.1 M HNO3 (a), while 3 or
4 times are enough in 0.1 M HCl (b). This diﬀerence
results in diﬀerent experimental times for one cycle (thetotal time of anion-exchange part, back extraction part,and conditioning part); 5 min for 0.1 M HNO3 (9 backextractions), and 3 min for 0.1 M HCl (3 back extractions). We decided to use 0.1 M HCl as the solution forback-extraction since the experiments for 261 Rf shouldbe performed in shorter cycles.
We performed about 100 cycles of the following sequence; 60 s of anion exchange with 8 M HNO3 , followedby 4 back extractions with 0.1 M HCl, and then 2 iterations of conditioning with 8 M HNO3 . The Kd valuesof Zr, Hf, and Th in the anion exchange were constantin 100 consecutive runs using AMBER, and this result
indicates that the Adogen 464 resin has suﬃcient durability to conduct a repetitive anion-exchange experimentof 261 Rf.
In the near future, an on-line experiment of Zr and Hf
will be conducted as a model experiment for Rf underthe experimental conditions determined in this study.

(1)
References
1) T. Yokokita et al., Dalton Trans. 45, 18827 (2016).
2) T. Yokokita et al., RIKEN Accel. Prog. Rep. 52, 187 (2019).
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