Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 47 (2014)

Coprecipitation experiment of various elements with Sm hydroxideusing multitracer
Y. Kasamatsu,＊1 K. Toyomura,＊1,＊2 T. Yokokita,＊1,＊2 H. Haba,＊2 J. Kanaya,＊2 Y. Kudou,＊2 and A. Shinohara＊1,＊2
Chemical studies on transactinide elements with atomic
numbers Z ≥ 104 are currently at the frontier in nuclear
chemistry. The transactinide elements are produced ataccelerators using heavy-ion-induced nuclear reactions.
Rapid chemistry on a one-atom-at-a-time basis is applied tothese elements because of their low production rates andshort half-lives. In addition, for unambiguous identificationof these elements, it is necessary to detect α or spontaneous
fission decays. Therefore, chemical experiments oftransactinides are not abundant. In the ion-exchange
chromatography, the fluoride complex formation of Rf (Z =104) was successfully investigated, and the behavior of Rf
was reported to be clearly different from those of thehomologues Zr and Hf. Chemical studies on transactinides
in various chemical systems should be conducted tounderstand their characteristic chemical properties.
The purpose of the present study is to establish acoprecipitation method as a new method for the chemistryof transactinide elements. Because these elements can betreated as only one atom at a time, we must study theircoprecipitation behaviors with a carrier element. For this, apreparation method of coprecipitated samples with Smhydroxide, which facilitated the α spectrometry with a highenergy resolution, was established.1) We are planning toapply this method to transactinide chemistry and toinvestigate the coprecipitation behaviors of transactinides.
In the chemistry of transactinides, model experiments with
their homologues are usually performed to establish theexperimental method and to determine the conditions. In
this work, we investigated the coprecipitation behaviors ofvarious elements with Sm hydroxide using a multitracer
produced by nuclear spallation reactions in RIKEN.
A multitracer was produced by irradiating the natTa foil
targets by 135-MeV/nucleon 14N ions accelerated by
RIKEN Ring Cyclotron2). Various nuclides, namely variouselements, with Z < 73 (Ta) were produced by nuclear
spallation reactions. Only the nuclear reaction products
recoiling out of the target foils were transported from thereaction chamber to the chemical laboratory by the He/KClgas-jet system.2) The products collected on a glass filter
paper for about 40 h were dissolved in 1 mL of 0.01 M HClsolution, and the solution sample was filtrated with a filter
paper to remove the glass chips from the solution.
The Sm standard solution (20 µL) containing 20 µg of
Sm was added into 220 µL of the multitracer solution. Thesolution was stirred, and then 2 mL of the basic solution(dilute and concentrated aqueous NH3, and 0.1, 1, 6, and 12

M NaOH solutions) was added. The solution was stirred for10 s or 10 min. Then, the solution containing the precipitate
was filtrated by suction with a polypropylene membranefilter (0.1 µm, φ20, Eichrom). The filtrate was collected in avial. Both the precipitate and filtrate were dried using aheater at 100°C and then subjected to γ-ray spectrometry
with a Ge detector. The precipitation yields (Y1) weredetermined from these radioactivities. The reference
radioactivities of the radiotracers were also determined. Theprecipitation yield (Y2) as a relative value to the reference
was also determined to check the accuracy of the obtained
precipitation yields.
The product nuclides were identified from the energies
and half-lives of the observed γ-ray peaks. We found thefollowing nuclides: 24Na, 42K, 82mRb, 127,129Cs (alkalimetals), 28Mg, 47Ca, 128Ba (group 2), 44,47,48Sc, 87Y (group 3),
132,135
Ce, 145,146Eu, 146,147,149Gd, 149-153,155Tb, 155,157Dy, 160mHo,161
Er, 165,167Tm, 166,169Yb, 169,171,172Lu (lanthanides), 89Zr,170,173
Hf (group 4), 90Nb, 176Ta (group 5), 93mMo (group 6),
96
Tc (group 7), 99m,100Rh (group 9), 65Zn, (group 12), 67Ga,
110,111In (group 13), 71,72As, 118m,120mSb (group 15), 73Se, and119m
Te (group 16).
For these elements, the precipitation yields and theirdependences on the composition of the basic solution wereobtained. Overall, the yields reflecting the properties ofeach element in the hydroxide precipitation were observed.
For example, the yields of alkali metal elements werealmost 0% under all the conditions. The yields oflanthanides were almost 100%, and decreased in the caseusing 6 and 12 M NaOH. In addition, the precipitation yieldof Zn was decreased to almost 0% in adding concentrated
aqueous NH3, indicating the well-known properties that Zn
forms a cationic ammine complex in such a solution. The
yields of Zr and Hf, the homologues of Rf, were close to100% and decreased with an increase in the hydroxide-ion
concentration, while those of Nb and Ta, the homologues ofDb, were always high. In contrast, the yields of Mo, thehomologue of Sg, were 0% under all the conditions. Itwould be interesting to study the precipitation behaviors ofthese transactinides. The Y1 values were consistent with theY2 values. In comparison between the results with 10-s and
10-min stirring, both the yields agreed with each other for
many elements, suggesting rapid chemical reactions; onlyexception was the result using 12 M NaOH. We believe thatthe coprecipitation properties of transactinides with Smhydroxide could be investigated by the present method.

Graduate School of Science, Osaka University＊2RIKEN Nishina Center1) H. Kikunaga et al., Appl. Radiat. Isot. 2008, 67, 539.
2) H. Haba et al., Radiochim. Acta 2005, 93, 539.

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