Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

Online solid-liquid extraction of 255 No with the polymer-supported
crown ether
E. Watanabe,∗1,∗2 R. Nakanishi,∗1,∗2 S. Otaka,∗1,∗2 R. Wang,∗1,∗2 Y. Itakura,∗2,∗3 R. Masuda,∗1,∗2 Y. Shigekawa,∗2A. Nambu,∗2 X. Yin,∗2 T. Yokokita,∗4 H. Haba,∗2 A. Shinohara,∗1,∗5 and Y. Kasamatsu∗1,∗2∗1∗2∗3∗4∗5Graduate School of Science, Osaka University
RIKEN Nishina Center
School of Science, Osaka University
Salesian Polytechnic
Osaka Aoyama University

the automated rapid α/SF detection system.
After α-particle measurement, we measured γ-ray activities of 162 Yb in the samples with Ge detectors tocalculate the chemical yield of each extraction.
We carried out 48 extraction and 24 control cycles
and observed a total of 173 α events from the decay of255
No, as shown in Fig. 1. The production cross-sectionof 255 No was estimated to be approximately 500 nb, andthe value is consistent with that determined in the previous report.7) The half-life of 255 No was estimated to be212±24 s, which is in good agreement with the previously
reported value (211 ± 11 s).8) The Kd value of 154, 155 Erand 254, 255 Fm (byproduct α-emitters) is ∼1 mL g−1 ,which is within the value of other f-block elements previously reported.4) Thus, it was demonstrated that the αevents in the region of interest for 255 No in the α-particle
spectrum properly originate from only 255 No and that reliable Kd values were obtained in the present solid-liquid
extraction experiments using AMBER. The Kd values ofNo are under estimation.

CountsNobelium (No) is an actinide element with an atomic
number of 102. In aqueous solutions, No is considered to form a +2 valence state stably, while other f block elements are stable at +3 or higher valence states.
Previous ion-exchange experiments have reported thatNo exhibits similar chemical behavior to that of Ca2+and Sr2+ .1) Our group has recently demonstrated that
No2+ shows diﬀerent coprecipitation behavior from alkaline earth metal ions, using the samarium hydroxide
coprecipitation method.2) Further systematic studies areneeded on No2+ compared with the group II elementsfrom the viewpoint of molecular structure in the solution and its electronic structure.
We focus on solid-liquid extraction using the polymersupportedcrownether.
TheSrresin (Eichrom Inc.)
contains 4,4′ (5′ )-di-tertbutylcyclohexano-18-crown-6 ether (DtBuCH18C6) andhas strong extraction selectivity for Sr2+ . The selectivity of alkaline earth ion is aﬀected by a changes in theacidity of a liquid phase and its concentration.3,4) In theextraction in HNO3 system, the extracted species of Sr
is deduced to be Sr(NO3 )2 DtBuCH18C6.5) Previously,
we found that the extraction reaction of alkaline earthelements with the Sr resin rapidly (∼1 min) reached theequilibrium state and the solid-liquid extraction is suitable for 255 No experiment. We have obtained the distribution coeﬃcients (Kd ) of Ca, Sr, Ba, and Ra with theSr resin in HNO3 , HCl, and HClO4 as comparison datafor No.
In this work, we performed online solid-liquid extraction experiments with 255 No to obtain its Kd values andto investigate the complexation between No2+ and DtBuCH18C6. To obtain the Kd values of No under equilibrium state, we used a batch-type solid-liquid extraction apparatus called AMBER.6)
We produced 255 No (T1/2 = 211 s) and 162 Yb(T1/2 = 18.9 min) by the 248 Cm(12 C, 5n)255 No andnatGd(12 C, xn)162 Yb reactions with the AVF cyclotron
at RIKEN. The reaction products were transported by
the He/KCl gas-jet system to the chemistry room anddissolved in 3.5 MHNO3 or 7.6 M HCl solutions. Thesolution sample was injected into a chemical reaction
container containing the Sr resin. After shaking thecontainer for 60 or 180 s, only the solution phase wasdischarged from the container through a PTFE ﬁlter.
Subsequently, the discharged sample was evaporated todryness and subjected to alpha particle measurement by255No

Energy / keVFig. 1. α-spectrum for 255 No obtained in control experiment
without the resin with 60-s shaking.

In the future, we will discuss the extraction behaviorof No based on the comparison of the Kd values of 255 No
with those of alkaline earth metal ions. Additionally, wewill perform relativistic quantum chemical calculations
and analyze the electronic states of extracted species ofNo.
References
1) R. J. Silva et al., J. Inorg. Nucl. Chem. 38, 1207 (1976).
2) H. Ninomiya et al., RIKEN Accel. Prog. Rep. 52, 184(2019).
3) E. P. Horwitz et al., Solv. Extr. Ion Exch. 10, 313 (1992).
4) D. V. Filosofov et al., Solv. Extr. Ion Exch. 33, 496 (2015).
5) M. L. Dietz et al., Talanta 62, 109 (2004).
6) Y. Kasamatsu et al., Radiochim. Acta 103, 513 (2015).
7) T. Sikkeland et al., Phys. Rev. 172, 1232 (1968).
8) M. Asai et al., Phys. Rev. C 83, 1 (2011).

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