Research Group for Superheavy Elements
Group Leader : Matthias Schädel
Members : Kazuaki Tsukada, Masato Asai, Tetsuya Sato, Atsushi Toyoshima, Zijie Li, Nozomi Sato,Kazuhiro Ooe, Yuichiro Nagame
Group Activities

The research objectives of this group are to understandchemical and nuclear properties of superheavy elements (SHEs)
placed at the uppermost end of the Periodic Table and on theheaviest frontier of the nuclear chart. To clarify the chemical
properties of SHEs, we investigate valence electronic structuresof SHEs through experimental determinations of ionizationpotentials, redox potentials, and compound formations of SHEs.
To elucidate the limits of stability of the heaviest nuclei, weinvestigate the shell structure of superheavy nuclei throughexperimental assignments of proton and neutron single-particle
orbitals and through the evolution of nuclear deformation at thehighest proton and neutron numbers.
Element 104, rutherfordium (Rf) is the first transactinoid
element. From the simple extension of the Periodic Table of theElements, Rf should belong to the group 4 transition metals.
Although chemical properties of Rf are expected to be similar
to those of lighter homologues Zr and Hf, some differences arefound in HCl and HF solutions [1,2], which provides valuable
information on the valence electronic structure of Rf.
Fluorido complex formation of Rf in HF/HNO 3 mixed
solution [3]In the present work, we have investigated the cationexchange behavior of 261 Rf (T 1/2 = 78 s) produced in the248
Cm(18O, 5n) reaction on a “one-atom-at-a-time” scale using
an automated ion-exchange separation apparatus coupled withthe detection system for alpha-spectroscopy (AIDA), together
with its lighter group-4 homologs Zr and Hf, and the tetravalent
pseudo-homolog Th in HF/HNO3 mixed solution. The results
demonstrate that distribution coefﬁcients (Kd) of Rf in HF/0.10 M
HNO3 decrease with increasing concentration of the fluorideion [F−] (Fig. 1). This resembles the behavior of the homologs,indicating the consecutive formation of ﬂuorido complexes ofRf. We also measured the Kd values of Rf and the homologs asa function of the hydrogen ion concentration [H+] in the rangeof [F−] = 5.29 × 10−7−3.17 × 10−6 M. The logKd values decreaselinearly with an increase of log[H +] with slopes between−2.1 and −2.5. This indicates that these elements are likely toform the same chemical compounds: mixture of [MF]3+ and[MF2]2+ (M = Rf, Zr, Hf, and Th) in the studied solution. It isalso ascertained that the fluorido complex formation of Rf isFig. 1 Distribution coefficients, K d, of Rf, Zr, Hf, and Th
between a cation-exchange resin CK08Y and 0.10 M
HNO3 plotted as a function of [F−].
13 ASRCsignificantly weaker than that of Zr and Hf, but it is stronger
than that of Th.
Sulfate complex formation of Rf in H 2SO 4/HNO 3 mixedsolution [4]The cation-exchange behavior of Rf was studied in 0.15−0.69
M H2SO4/HNO3 mixed solutions ([H+] = 1.0 M) using AIDA.
It was found that adsorption probabilities (%ads) of 261Rf on
cation-exchange resin decrease with an increase of [HSO4-],
showing a successive formation of Rf sulfate complexes.
Rutherfordium exhibits a weaker complex formation tendency
compared to the lighter homologues Zr and Hf. This is in good
agreement with theoretical predictions including relativistic
effects [5]. It was shown that the lower stability of the Rf
complexes is due to the smaller ionic contribution to thechemical bond, which is caused by the relativistic stabilizationof the 7s orbital, as well as the destabilization and spin-orbit
splitting of the 6d orbitals. It is also in agreement with its larger
ionic radius (76 pm) [6] in comparison with those of Zr (71pm) and Hf (72 pm) [7]. We like to compare this results withour previous report for the complex formation with fluorideions [2,3]. The trend of the ﬂuoride complex formation in thegroup-4 elements is Zr ≈ Hf > Rf > Th, being also in agreementwith theoretical predictions [8]. The smaller ionic contribution
to the metal–fluorine bonding was also responsible for theweaker ﬂuoride complexation of Rf in comparison with that ofZr and Hf [8].

Fig. 2 Variations of adsorption probabilities, %ads, of Rf, Zr,and Hf on a cation-exchange resin CA08Y as a functionof [HSO4-] in the H2SO4/HNO3 mixed solutions ([H+] =1.0 M).
References[1] H. Haba et al., J. Nucl. Radiochem. Sci. 3, 143 (2002).
[2] A. Toyoshima et al., Radiochim. Acta 96, 125 (2008).
[3] Y. Ishii et al., Bull. Chem. Soc. Jpn. 84, 903 (2011).
[4] Z. J. Li et al., Radiochim. Acta 100, 157 (2012).
[5] V. Pershina et al., Radiochim. Acta 94, 407 (2006).
[6] V. Pershina, “Theoretical chemistry of the heaviest elements”,
in The Chemistry of Superheavy Elements (M. Schädel, ed.),Kluwer Academic Publisher, Dordrecht (2003).
[7] R. Shannon, Acta Cryst. A 32, 751 (1976).
[8] V. Pershina et al., Radiochim. Acta 90, 869 (2002).