RIKEN Accel. Prog. Rep. 50 (2017)

Ⅰ. HIGHLIGHTS OF THE YEAR

Observation of the chemical reaction equilibria of element 104, rutherfordium:Solid--liquid extraction of Rf, Zr, Hf and Th with Aliquat 336 resin from HCl†
T. Yokokita,䠆1 Y. Kasamatsu,䠆1 A. Kino,䠆1 H. Haba,䠆2 Y. Shigekawa,䠆1 Y. Yasuda,䠆1 K. Nakamura,䠆1 K. Toyomura,䠆1Y. Komori,䠆2 M. Murakami,䠆2 T. Yoshimura,䠆3 N. Takahashi,䠆1 K. Morita,䠆2 and A. Shinohara䠆1It is important to investigate the chemical properties ofsuperheavy elements (SHEs) with an atomic number (Z  
104. Especially, in solution chemistry, we can study various
non-volatile complexes. Thus far, two-phase partition
methods, such as ion exchange and extraction, have been
usually applied to SHEs. In these experiments, a rapid
chemical separation is repeated many times by online
chemical experiments using automated chemistry apparatus.
The distribution coefficient (Kd) in a solid-liquid extractionor the distribution ratio (D) in a liquid-liquid extraction isoften used in solution chemistry investigations for SHEs.
These values are defined as the ratio of the elemental(radioactivity) concentrations of the two phases atequilibrium. However, there have been no previous
experimental observations of equilibrium states for SHEs,
although the experimental conditions in many previous
studies were carefully adjusted based on the behaviours ofhomologues. To obtain the equilibrium Kd values for SHEs,
we previously developed a new automated solid-liquid
extraction apparatus for online use (AMBER).1) Herein, weapplied the AMBER-based method to element 104, Rf.
In the online solid-liquid extraction of Rf and Hf, wesimultaneously produced 261Rf (t1/2 = 68 s) and 169Hf (t1/2 =3.24 min) by the bombardment of a 248Cm and natGd
mixture with 18O beams delivered by the K 70 AVF
cyclotron at RIKEN. The products were transported to achemistry room by a He/KCl gas-jet system. The
transported products were deposited on the collection site ofAMBER’s dissolution equipment for ~2 min, and weredissolved in HCl. The solution sample was injected into achemical reaction container containing 28 wt% Aliquat 336
resin (anion exchanger). After shaking the container with ashaker for 10, 30 and 60 s, only the solution phase wasdischarged from the container, passing through a PTFE
filter, by compressed air for 10 s. The discharged solution
was collected in a Ta disk on the round table of an
automated rapid D/SF detection system, and evaporated
quickly to dryness using hot He gas and the halogen heatlamp. Subsequently, using the detection system’s robot arm,
the Ta disk was rapidly transferred into an D-particle
detection chamber for D-particle measurements for ~800 s.
After that, the sample was assayed by J-ray measurementwith a Ge detector for the monitor of 169Hf. We also
performed control experiments without the resin todetermine the standard radioactivity of the solution sample.
†Condensed from the article in Dalton Trans. 45, 18827 (2016).
Graduate School of Science, Osaka University
䠆2RIKEN Nishina Center䠆3Radioisotope Center, Osaka University

Control experiments were carried out in 7.9 M HCl with10-s shaking and in 9.0 M HCl with 10-s and 30-s shaking.
Solid-liquid extraction experiments were carried out in 7.9M HCl with 10-, 30- and 60-s shaking and in 9.0 M HCl
with 10-s shaking. The ratios of the element concentrations
between the resin and solution phases (Qd) in mL gí1 were
determined from the radioactivities in the resin and thesolution phases, the volume of the solution phase, and themass of the dry resin.
The solid-liquid extraction of 89g,mZr and 173Hf in theonline experiment was performed at the Research Center for
Nuclear Physics (RCNP), Osaka University in a similar way
to the extraction of 261Rf. The solid-liquid extraction of 88Zr,
175
Hf and 234Th in the offline experiments (usual batchmethod) was also performed.
In the Rf experiment, we conducted a total of 379
extraction procedure cycles, and registered 132 D eventsfrom the decay of 261Rf and its daughter nuclide 257No (t1/2 =24.5 s), including 23 time-correlated D–D correlation. Theevent ratios of 261Rf between the resin and solution phases
were estimated from these D events.
The Qd values of Rf, Zr and Hf were constant in all thetime ranges studied, indicating that equilibrium in theextraction of Rf (7.9 M HCl), as well as Zr and Hf, wasaccomplished within 10 s. This finding represents the firstobservation of the equilibrium state of the extraction
reactions for SHEs on a one-atom-at-a-time basis, and theKd value of Rf at equilibrium was obtained. Based on theseresults, we performed extraction experiment of Rf in 9.0 M
HCl with shaking for 10 s, and obtained a lower limit for
the Kd value > 1.4 × 103 mL gí1 (95% confidence).
For the dependence of the Kd values of Rf, Zr, Hf and Th
on the HCl concentration, the Kd values of Zr and Hf in theonline experiment were in good agreement with those in theoffline experiment. The Kd value of Rf in 9.0 M HCl washigher than that in 7.9 M HCl, which indicates that theabundance of anionic chloride complexes of Rf increases
with increasing the HCl concentration. The Kd value of Rf
was close to that of Zr in 7.9 M HCl, while the value of Rf
in 9.0 M HCl was clearly higher than the values of Zr and
Hf by one and two orders, respectively. The significant
difference in the Kd values among Rf, Zr and Hf in the HClsystem was shown for the first time in this study bydetermining the Kd values of Rf. This result might suggest
the possibility that Rf forms chloride complexes with adifferent configuration to its lighter homologues.

䠆1Reference1) Y. Kasamatsu et al.: Radiochim. Acta 103, 513 (2015).

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