Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 48 (2015)

Coprecipitation Behaviors of Zr, Hf, and Th with Sm Hydroxide
for Chemical Study of Element 104, Rf†
Y. Kasamatsu,＊1 K. Toyomura,＊1 N. Shiohara,＊1 T. Yokokita,＊1 Y. Komori,＊1,＊2 A. Kino,＊1 T. Yoshimura,＊3 N. Takahashi,＊1H. Haba,＊2 Y. Kudou,＊2 H. Kikunaga,＊2,＊4 T. Mitsugashira,＊5 T. Ohtsuki,＊6 K. Takamiya,＊6 and A. Shinohara＊1Owning to significant relativistic effects on electron
orbital shells for heavy elements, the chemical properties ofthe superheavy elements are expected to deviate from thecharacteristic periodicity of the lighter homologues in theperiodic table, and their chemical studies have attracted
much attention. However, experimental evaluation of these
species is fraught with difficulties. Because of theextremely low production rates and short half-lives (withina few min) of these heavy nuclides, chemical evaluations of
the superheavy elements must be rapidly conducted on a
one-atom-at-a-time basis. Thus, simple chemistry
employing partition methods such as solvent extraction andion-exchange chromatography have been utilized and thechemical separations were repeated hundreds or thousandsof times under identical conditions. This approach requires
a rapid chemistry apparatus. Additionally, for unambiguous
identification of superheavy nuclides, it is necessary tomeasure the energies and lifetimes of α or sometimes
spontaneous fission decays.
The purpose of the present study is to establish a newexperimental methodology for investigating the chemical
properties of superheavy elements, specifically, thecoprecipitation properties of 261Rf (T1/2 = 68 s) by theformation of hydroxide and ammine complexes. Herein, weapplied a simple coprecipitation method with Sm hydroxide,
which facilitates α spectrometry with high energyresolution,1) to the investigation of the coprecipitation
behaviors of the homologues of Rf: Zr, Hf, and Th. In
addition, a semiautomatic apparatus for repetitive
preparation of precipitate samples was developed and tested
using the gas-jet transport system of nuclear products.
We used 88Zr, 175Hf, and 228Th radiotracers to prepare
coprecipitated samples with Sm hydroxide. A 20 μL aliquotof the Sm standard solution (Sm 1000 ppm, 1 M HNO3)
was added into 220 μL of an aqueous solution (~0.4 M HCl)containing the radiotracers in a polypropylene (PP) beaker.
The solution was stirred and 2 mL of the basic solution(dilute and concentrated aqueous NH3 and 0.1, 1.0, 6.0, and12.0 M NaOH solutions) was then added to produce theprecipitate. After aging the precipitate for 10 s or 10 min at
25 ºC, the precipitate sample was subjected to suction
filtration with a PP membrane filter (eichrom, Resolve®
†Condensed from the article in J. Nucl. Radiochem. Sci. 14, 7 (2014).
Graduate School of Science, Osaka University＊2
RIKEN Nishina Center＊3
Radioisotope Research Center, Osaka University＊4
Research Center for Electron Photon Science, Tohoku University＊5
Institute for Material Research, Tohoku University＊6
Research Reactor Institute, Kyoto University＊1

Filters 0.1 μm). The obtained sample was dried on a heaterat 100 ºC, and was subjected to γ-ray and α-particle
measurements. The radioactivities of the filtrate and PP
beakers used were also measured. We determined
precipitation yields, Y, and the percent adsorption on the PP
beaker, Rad, from the radioactivities.
A computer-controlled suction filtration apparatus for thepreparation of precipitated samples of heavy elements wasdeveloped. The online experiment using the apparatus wasperformed with relatively short-lived nuclides 89m,gZr (4.2min and 78.4 h) and 173Hf (23.6 h) produced using the AVF
cyclotron at RCNP. These nuclides were rapidly andcontinuously transported from the nuclear reaction chamberto the chemistry laboratory using the He/KCl gas-jet system.
Using the apparatus, the products were dissolved by 200 μLof dilute HCl and the precipitate samples were prepared atroom temperature in a manner similar to that used in theabove tracer experiment with stirring for 10 s.
The Rad values of Zr, Hf, and Th for samples aged for 10s was generally less than 3%, which suggests that physicaladsorption of these group 4 elements during coprecipitation
with Sm hydroxide was small enough to be negligible in thedetermination of the coprecipitation yields. The Y values ofZr, Hf, and Th obtained with 10-min and 10-s aging are ingood agreement with each other. This suggests that thechemical reactions during coprecipitation of these elements
are fast, and the present conditions are suitable for
evaluating the coprecipitation behavior of 68-s 261Rf.
Almost complete coprecipitation of Zr and Hf with Smhydroxide was achieved when aqueous NH3 solutions and
0.1 M NaOH were used. These results are consistent withthe well-known properties of these elements, i.e., hydroxide
precipitation in basic solutions. With the use of more highly
concentrated NaOH solutions, these yields decreased,
whereas the Th yields were constant at ca. 100%. This is
attributed to the fact that Zr and Hf form hydroxide
complex ions in high [OH−] solutions.
The Y values obtained in the online experiments and theirdependence on the composition of the added basic solution
are consistent with those in offline experiment. Thissuggests that the present experimental method using theapparatus under the present conditions should be applicableto the coprecipitation experiment of Rf.
Reference1) H. Kikunaga et al., Appl. Radiat. Isot. 67, 539 (2008).

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