RIKEN Accel. Prog. Rep. 50 (2017)

Ⅲ-3. Radiochemistry & Nuclear Chemistry

Coprecipitation experiment with Sm hydroxide using a multitracer producedby nuclear spallation reaction: A tool for chemical studies with superheavyelements†
Y. Kasamatsu,䠆1 T. Yokokita,䠆1 K. Toyomura,䠆1 Y. Shigekawa,䠆1 H. Haba,䠆2 J. Kanaya,䠆2 M. Huang,䠆2 Y. Ezaki,䠆2T. Yoshimura,䠆3 K. Morita,䠆2 and A. Shinohara䠆1
The chemical properties of superheavy elements (SHEs)
are expected to deviate from the periodicity of their lighter
homologues in the periodic table because of the strong
relativistic effects on the valence electronic shells of theheavy atoms. However, it is difficult to perform chemical
experiments of SHEs because these nuclides are short-lived
and their production rates by nuclear reactions are quite low.
These conditions create the need for rapid chemical
experiments on a one-atom-at-a-time basis. In addition, forunambiguous identifications of these elements existing as
VLQJOH DWRPV LW LV QHFHVVDU\ WR GHWHFW Į SDUWLFOHV ZLWKcharacteristic energies. These experimental difficulties limit
the variety of chemical investigations of SHEs. So far, mostof the methodologies in aqueous chemistry were limited tothe ion-exchange method or solvent extraction. The purposeof the present study is to establish a coprecipitation method
as a new methodology to explore the chemistry of SHEs. In
the present study, a multitracer which contains various
radioisotopes (various homologues of SHEs) was used toinvestigate the applicability of the coprecipitation
experiment with Sm hydroxide to SHE chemistry.
The multitracer was produced by irradiating natTa targets(2-ȝP WKLFNQHVV î  IRLOV  ZLWK 14N7+ ions accelerated to135 MeV per nucleon by the RIKEN ring cyclotron (~1.6
HOHFWULF ȝ$) IRU  K. Various nuclides, namely variouselements, with Z   7D  ZHUH SURGXFHG E\ QXFOHDU
spallation reactions. Only the nuclear reaction products
recoiling out of the target foils were attached to KCl
aerosols seeded in a He gas and transported from thenuclear reaction chamber to the chemical laboratory by aHe gas jet through a PTFE capillary tube.1) The transported
products were collected on glass filter paper, and were
GLVVROYHGLQP/RI0+&O.
,Q D SRO\SURS\OHQH 33  EHDNHU  ȝ/ RI 6P VWDQGDUGVROXWLRQ PJ/í1, 1 M HNO3 ZDVDGGHGLQWRȝ/
of the prepared multitracer solution. The solution wasstirred, and then, 2 mL of the basic solution (dilute andconcentrated aqueous NH3 DQG    DQG  0
1D2+VROXWLRQV ZDVDGGHG7KHVROXWLRQZDVVWLUUHGIRUVRUPLQDWURRPWHPSHUDWXUHWRGHWHUPLQHWKHFKHPLFDO
reaction time required to reach equilibrium. Then, thesolution containing the precipitate was filtrated by suction
witK D 33 PHPEUDQH ILOWHU HLFKURP 5HVROYH )LOWHUV †Condensed from the article in Appl. Radiat. Isot. 118,  16)
Graduate School of Science, Osaka University
䠆2
RIKEN Nishina Center䠆3
Radioisotope Center, Osaka UniversityȝP  %RWK WKH SUHFLSLWDWH DQG ILOWUDWH ZHUH GULHG XVLQJ DKHDWHU DW  & 7KH SUHFLSLWDWH ILOWUDWH DQG 33 EHDNHU
used were subjected to Ȗ-ray spectrometry with Ge
semiconductor detectors. The standard activities of theradiotracers were also determined. The precipitation yields
were evaluated from these radioactivities.
The product nuclides were identified based on their
FKDUDFWHULVWLF Ȗ-ray energies and corresponding half-lives.
,QWRWDOZHLGHQWLILHGHOHPHQWVFRQWDLQLQJPRUHWKDQnuclides as follows: 24Na, 42K, 82mRb, 127,129Cs {group 1},
28
Mg, 47Ca, 128,(131)%D^JUoup 2}, 44,47,48Sc, (86),87g,(m)Y {group3}, (132La), 132,135Ce, 145,146,(147)Eu, 146,147,149Gd, 149-153,155Tb,
152,155,157
Dy, (PHo), 161Er, 165,(166),167Tm, 166,(169)Yb,
  
Lu {group 3 (lanthanides)}, (86,87)89Zr, Hf{group 4}, Nb, 176Ta {group 5}, 93mMo {group 6}, 96Tc{group 7}, P P Rh {group 9}, 65Zn {group 12}, 67Ga,
In {group 13}, 71,72As, PPSb {group 15}, 73Se,119m
Te {group 16}. The nuclides listed in parenthesesandare ones for which the coprecipitation yields could not bedetermined. Various elements belonging to various groups
in the periodic table were included in the multitracer used.
The presently prepared multitracer contains the homologuesof various (nine) SHEs (group 4–18), and thus, this study isbeneficial for the model experiment toward the chemical
study on the SHEs.
The coprecipitation yields of radionuclides of groups 1–7,
9, 12, 13, 15, 16 elements with Sm hydroxide and theirdependence on the kind and concentration of the preparedbasic solutions qualitatively reflect the hydroxide
precipitation properties (formation of ammine andhydroxide complexes) of the elements in macro amounts.
This finding suggests that the coprecipitation behavior of anelement whose chemical properties are unknown can beinvestigated using the present method, and we can discuss
its general hydroxide precipitation properties based on theresults obtained for coprecipitation. In addition, thechemical reactions of the majority of the elements in thecoprecipitation are sufficiently fast to reach equilibrium
ZLWKLQ  V RI VWLUULQJ DOWKRXJK IRU 0R DQG 6H UHODWLYHO\slow chemical reactions were observed. %DVHG RQ WKHresults in the present experiment, we can say that thepresent coprecipitation method with Sm hydroxide isapplicable to SHE chemistry. This methodology will open
new chemistry routes (various precipitates) for SHEs.

䠆1Reference1) H. Haba et al.: Radiochim. Acta 93, 539 5).

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