III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Anion exchange of Rf in H2 SO4 using the batch-type solid-liquid
extraction apparatus AMBER
T. Yokokita,∗1 Y. Kasamatsu,∗2 E. Watanabe,∗2 Y. Komori,∗1 Y. Shigekawa,∗1 Y. Wang,∗1 D. Mori,∗1H. Ninomiya,∗2 S. Hayami,∗2 K. Tonai,∗2 K. Ghosh,∗1 A. Shinohara,∗2 and H. Haba∗1
The relativistic eﬀect on orbital electrons is relatively more pronounced for heavy elements. In particular, the chemical properties of superheavy elements(SHEs) with atomic number Z ≥ 104 are expected
to deviate from the periodicity of their lighter homologues in the periodic table. Thus, it is importantand interesting to investigate the chemical propertiesof SHEs. So far, ion-exchange experiments on SHEs
have been conducted to determine the distribution coeﬃcients (Kd ), which are deﬁned as the ratio of the elemental concentrations of the two phases.1) However,those values at equilibrium have not been obtained inmost studies. To obtain the Kd values at equilibrium,
the batch-type solid-liquid extraction apparatus called
AMBER was developed,2) and the equilibrium Kd values on the chloride complexation of Rf were successfully obtained in an Aliquat 336/HCl system.3)
To study the sulfate complexation of Rf, we plan toperform anion-exchange experiments of Rf and its homologous elements. In our previous study, by using
AMBER, we obtained the Kd value of Rf in 0.11 M
H2 SO4 .4) The obtained Kd value of Rf is ∼10 mL g−1 ,probably indicating that Rf does not form anionic2−species or that counter ions of HSO−
4 and SO4 inhibit
the adsorption of Rf on the anion-exchange resin. In
this study, to reduce the eﬀect of counter ions, we performed an anion-exchange experiment of Rf in 0.060 M
H2 SO4 , which is lower than 0.11 M.
In the anion exchange of Rf and Hf, we simultaneously produced 261 Rf (T1/2 = 68 s) and 169 Hf (T1/2= 3.24 min) by the bombardment of a mixture of248
Cm and natGd with an 18 O beam delivered fromthe K70 AVF cyclotron at RIKEN. The products weretransported to a chemistry room by a He/KCl gasjet system. The transported products were depositedon the collection site of AMBER’s dissolution equipment for 3 min and dissolved with 0.24 mL of 0.060,0.30, and 0.46 M H2 SO4 . The solution sample wasinjected into a chemical reaction container containing
the anion-exchange resin (MCI GEL CA08Y). Aftershaking the container with a shaker for 10, 30, and90 s, only the solution phase was discharged from thecontainer through a PTFE ﬁlter with compressed air.
The discharged solution was collected in a Ta disk on
the round table of an automated rapid α/SF detection system5) and evaporated quickly to dryness using
hot He gas and a halogen heat lamp. Subsequently,
the Ta disk was transferred to the position under a∗1∗2Si PIN photodiode detector, and α-particle measurement was performed. After the α-particle measurement, the γ-ray was measured with a Ge detector tomonitor 169 Hf. We also performed control experimentswith 10-s shaking without the resin to determine thestandard radioactivity of the solution sample. The Kdvalues were determined from the radioactivity in theresin and solution phases, the volume of the solution
phase, and the mass of the dry resin.
We conducted 390 anion-exchange and 92 control
cycles, and observed a total of 73 α events from thedecay of 261 Rf and its daughter nuclide 257 No (T1/2 =24.5 s), including 10 time-correlated α–α correlations.
The radioactivity ratios of 261 Rf between the resin andsolution phases were estimated from the α events. In
0.060 M H2 SO4 , the Kd values of Hf were constantin all the studied time ranges, indicating that equilibrium in the anion exchange of Hf was accomplishedwithin 10 s. Those of Rf were also constant in all thetime ranges studied, yielding values of approximately
20 mL g−1 . This indicates that Rf is not adsorbed onthe resin.
We also obtained the Kd values of Rf, Zr, Hf, andTh in 0.060–0.46 M H2 SO4 . The obtained Kd values ofRf are low (≤25 mL g−1 ) in the entire studied H2 SO4concentration range. In contrast, the Kd values of Zr,
Hf, and Th are ≥70 mL g−1 at 0.060 M H2 SO4 . Theseresults suggest that Rf does not form anionic species
and that Zr, Hf, and Th form anionic species in thisstudied condition. The Kd values at 0.060 M H2 SO4follow the order of Zr > Hf ≫ Th > Rf, and this sequence is consistent with the trend predicted by theoretical calculation.6) On the other hand, the sequenceof Kd values is Th > Rf > Hf ≥ Zr in the cation exchange in the H2 SO4 /HNO3 system.7) In the future,
we plan to discuss the chemical species of Rf in thisstudied condition from the obtained anion-exchange
behavior of Rf, Zr, Hf, and Th and chemical species ofZr, Hf, and Th.
References
1) Y. Nagame et al., Nucl. Phys. A 944, 614 (2015).
2) Y. Kasamatsu et al., Radiochim. Acta 103, 513 (2015).
3) T. Yokokita et al., Dalton Trans. 45, 18827 (2016).
4) T. Yokokita et al., RIKEN Accel. Prog. Rep. 53, 165(2020).
5) H. Haba et al., RIKEN Accel. Prog. Rep. 45, 204 (2012).
6) V. Pershina et al., Radiochim. Acta 94, 407 (2006).
7) Z. J. Li et al., Radiochim. Acta 100, 157 (2012).

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Graduate School of Science, Osaka University- 148 -1