Ⅲ-3. Radiochemistry & Nuclear Chemistry
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Coprecipitation behavior of element 102, nobelium, with barium
sulfateS. Otaka,∗1,∗2 E. Watanabe,∗1,∗2 R. Nakanishi,∗1,∗2 R. Masuda,∗1,∗2 R. Wang,∗1,∗2 Y. Itakura,∗2,∗3T. Yokokita,∗2,∗4 Y. Shigekawa,∗2 A. Nambu,∗2 X. Yin,∗2 H. Haba,∗2 A. Shinohara,∗5 and Y. Kasamatsu∗1,∗2∗1∗2∗3∗4∗5

determining the total amount of dissolved species (astandard sample is prepared), the reaction products
were dissolved in dilute HCl solution, and the solution
was put on a Ta plate. The sample was evaporated todryness by He gas at 600◦ C and a halogen heat lamp.
Finally, these dried precipitated and standard samples
were subjected to alpha-particle measurement by theautomated rapid alpha/SF detection system. After thealpha-particle measurement, gamma-ray activities of162
Yb in the samples were measured with a Ge detector to monitor the chemical yields and coprecipitation
behavior of Yb.
We successfully prepared 17 coprecipitated samples
and 41 standard samples. Alpha-particle spectrum
for the standard samples is shown in Fig. 1. Basedon the alpha counts, we estimated the coprecipitation
yields of 255 No and 162 Yb, considering various corrections such as the diﬀerences in the cooling times before the measurements and detection eﬃciency. As aresult, a high coprecipitation yield of around 80% wasobtained for 255 No in the case of adding 2.0 M ammonium sulfate. A detailed analysis is underway. We
plan to discuss the sulfate complexation properties of255
No based on the comparison with those of alkaline
earth metal elements. In addition, we will compare theresults with those obtained by quantum chemical calculations which were previously performed4) to discuss
the chemical bonding properties of No.

10255

8Counts

The orbital electrons of heavy elements with Z ≥101, synthesized by heavy-ion-induced nuclear reactions, are aﬀected by signiﬁcant relativistic eﬀects.
Therefore, the chemical properties of the heavy elements might be diﬀerent from those expected from theperiodicity of the homologues in the periodic table,
and it is very interesting to investigate their chemicalbehavior.
We focus on element 102, nobelium (No). No isreported to exist as M2+ ion in aqueous solutions,whereas the other heavy actinides all form M3+ .1,2) In
the previous chemical experiments on No, the behaviorof No was compared with those of divalent transition
metal elements and the alkaline earth metal, barium(Ba). As a result, it has been reported that No behaves similarly to Ba. Thereafter, No was reported
to have similar chemical behavior to those of calcium(Ca) and strontium (Sr), which have similar ionic radii
to No, instead of other alkaline earth metal elements.4)
Recently, our research group focused on sulfate precipitates of alkaline earth metal elements and established
the barium-sulfate-coprecipitation method which is applicable to No.3) According to the results obtained in
the preliminary experiments with Ca, Sr, Ba, and Ra,
we found that the precipitation behavior in the present
reaction system is sensitive to the ionic radii of the alkaline earth metal elements. In addition, it is expectedthat a diﬀerence in chemical bonding properties of No
from those of alkaline earth metal elements will be observed. In this study, we applied the above method toNo.
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, respectively, using theAVF cyclotron at RIKEN RIBF. The reaction products were transported by the He/KCl gas-jet system tothe chemistry room and dissolved in a dilute HCl solution. When a precipitated sample is prepared, 20 µgof Ba and 2 mL of 0.1 M or 2.0 M ammonium sulfate
were added into the dissolved solution in a 5-mL microtube, and the solution was stirred for 5 min at room
temperature using a Vortex mixer. Then, the solution
containing the precipitate was ﬁltrated using the suction ﬁltration apparatus controlled by PC. The precipitated sample was dried with He gas at 100◦ C. When214

NoPo

64
2075008000
Energy /keV8500

Fig. 1. Alpha-particle spectrum for the 255 No standard
sample.

References
1) J. Maly et al., Science 160, 1114 (1963).
2) G. T. Seaborg, in The Transuranium Elements(McGraw-Hill, New York, 1949), p.1492.
3) R. J. Silva et al., Inorg. Chem. 13, 2233 (1974).
4) S. Hayami, MS thesis, Osaka University (2021).

Graduate School of Science, Osaka University
RIKEN Nishina Center
Department of Chemistry, Osaka University
Salesian Polytechnic
Osaka Aoyama University- 143 -