Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 47 (2014)

Online coprecipitation experiment of 85Zr and 169Hf with Sm hydroxide
for chemical study of Rf
Y. Kasamatsu,＊1 K. Toyomura,＊1,＊2 T. Yokokita,＊1,＊2 Y. Komori,＊1 Y. Shigekawa,＊1,＊2 H. Haba,＊2 J. Kanaya,＊2M. Huang,＊2 M. Murakami,＊2,＊3 K. Morita,＊2 H. Kikunaga,＊2,＊4 and A. Shinohara＊1,＊2
Elucidating chemical properties of transactinide elementswith atomic numbers Z ≥ 104 is an intriguing and important
topic. Transactinide elements are produced at accelerators
using heavy-ion-induced nuclear reactions. The production
rates of these elements are low and their half-lives are short(T1/2 ≤ ~1 min). Thus, chemical studies on these elements
are conducted on a one-atom-at-a-time basis using rapid
chemical separation techniques, and products transported
online by a gas-jet system from a nuclear reaction chamber
are used. For unambiguous identification of a single atom,
detection of α or spontaneous fission decay is required.
Owing to these difficulties, so far, simple partition methods
such as gas-phase and aqueous-phase chromatographic
experiments have been applied to the studies oftransactinide elements.
Recently, the anion- and cation-exchange behaviors ofrutherfordium (Rf, Z = 104) in HF and HF/HNO3 solutions
were successfully investigated at the Japan Atomic Energy
Agency Tandem Facility, the behaviors of Rf was reported
to be different from those of its homologues Zr and Hf.1)
Detailed studies on Rf in various chemical systems areneeded for a further understanding of its chemical
properties. To establish a new chemical experiment forsuperheavy elements, thus far, we have developed a method
to rapidly prepare a coprecipitated sample, which has goodenergy resolution in alpha spectrometry. For thecoprecipitation study of Rf, we have studied coprecipitation
properties of group-4 elements, Zr, Hf, and Th with
Sm(OH)3,2) and also developed an apparatus for rapid
preparation of precipitate samples. In this study, weperformed online coprecipitation experiments of 85Zr and169
Hf using the developed apparatus, and determined theexperimental conditions for Rf.
We produced carrier-free radiotracers 85Zr (T1/2 = 7.9min) and 169Hf (T1/2 = 3.25 min) in the natGe/natGd(18O, xn)
reactions using the RIKEN K70 AVF cyclotron. The
reaction products were transported online by a He/KClgas-jet system to the chemistry laboratory. They weredeposited on the collection site of a dissolution apparatus,
and then dissolved in 120 µL of a 0.46 M HNO3 solution
containing Sm ions (460 mg/L). Various compositions ofbasic solutions (dilute and concentrated aqueous NH3, 0.15,
1, 6, and 12 M NaOH) were added into the sample solution.
The resultant concentrations were 0.28 and 13 M NH3,and 0.08, 0.84, 5.3, and 11 M NaOH, respectively. After
stirring the sample for 10 s, the coprecipitate sample wasprepared by suction filtration on a polypropylene membranefilter (0.1 µm, φ20, Eichrom) using a semiautomatic
filtration apparatus for repetitive experiments. The sample
was dried using a heater at 100 °C and was subjected to
γ-ray measurement using a Ge detector. On the other hand,radioactivities of the products dissolved using thedissolution apparatus were also determined. From the ratioof the measured radioactivities of the precipitate to those of
the dissolved solution, precipitation yields of Zr and Hf
were determined.
The dependence of the yield on the composition of theadded basic solution is depicted in Fig. 1. It was found that
almost the entire amounts of Zr and Hf were coprecipitatedwith Sm hydroxide when aqueous NH3 and 0.1 M NaOH
were used. This suggests that Zr and Hf form a neutralhydroxide complex and coprecipitate with Sm(OH)3
precipitate in these basic solutions. For more concentrated
NaOH solutions, the yields decreased as the concentrationof the hydroxide ion increased, indicating that the Zr and Hfform anionic hydroxide complexes. These results areconsistent with those obtained in the offline coprecipitation
experiment using 88Zr and 175Hf.2) It was found that thecoprecipitation yields of Zr and Hf with Sm hydroxide in
the rapid and online precipitation experiment can beobtained using the developed apparatus connected to theaccelerator at RIKEN; the present experimental systems areapplicable to Rf experiments.
Very recently, we indeed produced 261Rf in a 248Cm(18O,5n)261Rf reaction and performed the first trial of
coprecipitating Rf with Sm(OH)3. Approximately 43 alphaevents were detected in the energy region of 261Rf.

Fig. 1. Coprecipitation yields of 85Zr and 175Hf.

Graduate School of Science, Osaka University＊2
RIKEN Nishina Center＊3
Department of Chemistry, Niigata University＊4
Research Center for Electron Photon Science, Tohoku University＊1

References

1) Y. Ishii et al.: Bull. Chem. Soc. Jpn. 84, 903 (2011).
2) Y. Kasamatsu et al.: RIKEN Accel. Prog. Rep. 43, 270 (2010).

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