III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Production of 266 Bh in the 248 Cm(23 Na, 5n)266 Bh reaction and its decayproperties†
H. Haba,∗1 F. Fan,∗2 D. Kaji,∗1 Y. Kasamatsu,∗3 H. Kikunaga,∗4 Y. Komori,∗1 N. Kondo,∗3 H. Kudo,∗5K. Morimoto,∗1 K. Morita,∗1,∗6 M. Murakami,∗7 K. Nishio,∗8 J. P. Omtvedt,∗9 K. Ooe,∗10 Z. Qin,∗2 D. Sato,∗5N. Sato,∗1 T. K. Sato,∗8 Y. Shigekawa,∗1 A. Shinohara,∗3 M. Takeyama,∗11 T. Tanaka,∗12 A. Toyoshima,∗13K. Tsukada,∗8 Y. Wakabayashi,∗14 Y. Wang,∗1 S. Wulﬀ,∗9 S. Yamaki,∗1 S. Yano,∗1 Y. Yasuda,∗3 and T. Yokokita∗1Condensed from the article in Phys. Rev. C 102, 024625 (2020)
RIKEN Nishina Center∗2 Institute of Modern Physics, Chinese Academy of Sciences∗3 Graduate School of Science, Osaka University∗4 Research Center for Electron Photon Science, Tohoku University∗5 Department of Chemistry, Niigata University∗6 Department of Physics, Kyushu University∗7 Decommissioning and Radioactive Waste Management HeadOﬃce, Japan Atomic Energy Agency∗8 Advanced Science Research Center, Japan Atomic Energy
Agency∗9 Department of Chemistry, University of Oslo
∗10 Graduate School of Medicine, Osaka University∗11 Faculty of Science, Yamagata University∗12 Department of Nuclear Physics, Research School of Physics,
The Australian National University∗13 Institute for Radiation Sciences, Osaka University∗14 Center for Advanced Photonics, RIKEN†∗1248Cm(23Na,5n)266Bh

Cross section (pb)The decay properties of the neutron-rich and longlived isotopes 267 Bh and 266 Bh, which are located aroundthe deformed shell at Z = 108 and N = 162, were studied
in the 249 Bk(22 Ne, 5;4n)266, 267 Bh,1) 209 Bi(70 Zn, n)278 Nh→ 274 Rg → 270 Mt → 266 Bh,2) 243 Am(26 Mg, 3n)266 Bh,3)
and 248 Cm(23 Na, 5;4n)266, 267 Bh4) reactions. However,
the reported decay properties such as α energies andhalf-lives of the isotopes are not in good agreement.
In this work, we investigated the excitation functions
and decay properties of 266 Bh and 267 Bh via the248Cm(23 Na, 5;4n)266, 267 Bh reactions using the GARIS
gas-jet and MANON setups.5)
248
Cm2 O3 targets of 256–290 µg/cm2 thicknesses on
2-µm Ti backing foils were bombarded with a 23 Na7+
beam extracted from the RIKEN Heavy-Ion LINAC. The
beam energies at the middle of the target were 121.2,125.9, 130.6, and 135.3 MeV. The typical beam intensity
was 3 pµA. The evaporation residues (EVRs) of interest were separated in-ﬂight from the beam particles andthe majority of the nuclear transfer products by GARIS.
At the focal plane of GARIS, the EVRs passed througha Mylar vacuum window foil of 0.7-µm thickness andentered the gas-jet chamber, where the EVRs were thermalized in He gas, attached to KCl aerosol particles, andtransported through a Teﬂon capillary (2.0-mm i.d. ×10-m length) to the rotating wheel apparatus MANON
for α/SF-spectrometry. In MANON, the aerosol particles were deposited on a Au-coated (5 nm) Mylar foilof 0.5-µm thickness, forty of which were set on the periphery of a rotating wheel. The wheel was stepped toposition the foils between 15 pairs of Si PIN photodiodes(Hamamatsu S3204-09). The step intervals of MANONwere set to 5.0, 8.5, and 15.0 s.
We searched for time-correlated α-α and α-SF event

102101

248Cm(23Na,4n)267Bh

5n6n4n3n

100110

115

120

125

130

135

140

145

ELab (MeV)
Fig. 1. Cross sections for the 248 Cm(23 Na, 5;4n)266, 267 Bhreactions as a function of the laboratory-frame energy
ELab . The curves are the HIVAP calculations6) for the248Cm(23 Na, xn)271−x Bh reactions (x = 3–6).

pairs in a time window of 340 s. Consequently, a totalof 23 chains were assigned to 266 Bh, its daughter nuclide 262 Db, and granddaughter 258 Lr, while no chain
was assigned to 267 Bh. The α-particle energies of 266 Bhdisperse widely in the range of Eα = 8.62–9.40 MeV. The
reported α groups of Eα = 9.29 MeV,1) Eα = 9.08 and9.39 MeV,2) Eα = 9.03 MeV,3) and Eα = 8.82, 8.84–
8.99, and 9.05–9.23 MeV4) for 266 Bh are all within ourα-energy range, except for Eα = 9.77 MeV.2) The halflife of 266 Bh was measured to be T1/2 = 10.0+2.6−1.7 s,which is an order of magnitude longer than the previously reported values of T1/2 ≃ 1 s1) and T1/2 =3)
2)
0.66+0.59
and 5 times longer than T1/2 = 2.1+2.9−0.26 s,−0.8 s.
As shown in Fig. 1, the excitation function for the248
Cm(23 Na, 5n)266 Bh reaction was measured for theﬁrst time, and it indicates a maximum of σ = 57 ± 14 pb
at 130.6 MeV. The excitation function was reproducedby the statistical model code hivap.6) The upper-limit
cross section of σ ≤ 14 pb was also derived for the248
Cm(23 Na, 4n)267 Bh reaction at 121.2 MeV.
References

1) P. A. Wilk et al., Phys. Rev. Lett. 85, 2697 (2000).
2) K. Morita et al., J. Phys. Soc. Jpn. 81, 103201 (2012).
3) Z. Qin et al., Nucl. Phys. Rev. 23, 400 (2006).
4) K. Morita et al., J. Phys. Soc. Jpn. 78, 064201 (2009).
5) H. Haba et al., Chem. Lett. 38, 426 (2009).
6) W. Reisdorf, M. Schädel, Z. Phys. A 343, 47 (1992).

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