Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 47 (2014)

Solvent extraction behavior of 95gNb and 179Ta in HF medium
with tributyl phosphate
S. Tsuto,*1 M. Murakami, *1,*2 K. Ooe,*1 H. Haba,*2 J. Kanaya, *2 M. Huang,*2 S. Goto,*1 and H. Kudo*3
In a previous study,1) a long-lived isotope with a half-lifeof 27 h, 268Db, was assigned as the descendant nucleus of288
115 because of its similar chemical behavior to group-5elements. It was also reported that the chemical behavior ofDb was similar to that of Ta rather than of Nb.1) Recently, achemical experiment on 262Db (T1/2 = 34 s) has been carriedout in a mixed HF/HNO3 solution.2) In contrast, thisexperiment showed a contrary result that the chemical
behavior of Db is similar to that of Nb. Therefore, moredetailed studies on the chemical properties of Db are required
for the clear identification of element 115. In this study,
extraction behaviors of the lighter homologs of Db, Nb andTa, and the extraction kinetics is investigated toward thechemical identification of Db. To carry out chemical
experiments of Db on a atom-at-a-time scale, the chemical
studies of Nb and Ta should be conducted on a tracer scale.
Moreover, in the experiment on Db, rapid kinetics for theextraction equilibrium is required because only short-lived
radioisotopes of Db can be produced directly by heavy-ion
induced nuclear reactions. We tried solvent extraction with95g
Nb (T1/2 = 34.991 d) and 179Ta (T1/2 = 1.82 y) with tributyl
phosphate (TBP), which is widely used in the industrial
separation of Ta from Nb.3, 4)
The radiotracers of 95gNb and 179Ta were produced via
natZr(p,xn) and natHf(p,xn) reactions, respectively, using a 14MeV proton beam supplied by the RIKEN AVF cyclotron.5)
These tracers were chemically separated from the target
materials by means of anion exchange chromatography andstored in a 1 M HF solution. After evaporation of thissolution, HF solution with a desired concentration was added
to the tracers. One milliliter of the aqueous solution with thedesired HF concentration containing 95gNb and 179Ta tracers
was mixed with the same volume of 1.8 M TBP in 1, 2dichloroethane. The mixture was shaken mechanically for
180 min at 25C. After centrifugation, 700 L aliquots ofeach phase were taken separately. Gamma- and X-rays
emitted from the 95gNb and 179Ta tracers were measured usinga Ge detector. From these results, we calculated thedistribution ratio (D) :We also studied the extraction kinetics of this system bychanging the shaking time t (t = 0.2, 0.5, 1, 5, 10, 90, and 180min). In the experiment for investigating extraction kinetics
with 1.8 M TBP in 1, 2-dichloroethane and 5.4 M HF
solutions, the D values of 95gNb and 179Ta were almost
constant in the studied range of shaking time studied,suggesting that the extraction equilibrium is very fast.
Figure 1 shows HF concentration dependences of thedistribution ratios of 95gNb and 179Ta in 1.8 M TBP in 1, 2dichloroethane. When [HF]ini = 0.27 M, the D value of 179Ta
has a maximum of 346  58, while the value of 95gNb isapproximately 10-2. This indicates that Ta can be clearly
separated from Nb in the 0.27 M HF solution and thepredominant complex of Ta in HF solution varies near thisconcentration. Therefore, this experimental condition would
be suitable to investigate whether Db behaves like Nb or Ta.

For chemical experiments on short-lived Db, an on-line
rapid extraction apparatus is required. The development ofan apparatus utilizing a flow injection analysis system is inprogress.6) The on-line extraction of Nb and Ta from HF
solution into TBP will be performed using the apparatus.

Distribution ratio

10310210195g

Nb179Ta

10010-110-210-3 -31010-210-1100[HF]ini /M101102

Fig. 1. HF concentration dependences of distribution ratiosof 95gNb and 179Ta into 1.8 M TBP in 1, 2-dichloroethane.

D = (Aorg / Vorg) / (Aaq / Vaq),

References

1) N. J. Stoyer et al.: Nucl. Phys. A787, 388c (2007)
2) Y. Kasamatsu et al.: Chem. Lett. 38, 1084 (2009).
3) Z. Zhu and C. Y. Cheng: Hydrometallurgy 107, 1 (2011).
4) S. Nishimura et al.: Trans. JIM 5, 79 (1964).
5) M. Murakami et al.: Appl. Radiat. Isot. in press.
6) T. Koyama et al.: In this report.

where A is the radioactivity of the metals, and V is the volumeof each phase. The subscripts aq and org denote the aqueousand organic phases, respectively.
Graduate School of Science and Technology, Niigata University
RIKEN Nishina Center*3 Faculty of Science, Niigata University*1*2- 270 -