RIKEN Accel. Prog. Rep. 47 (2014)

HIGHLIGHTS OF THE YEAR

Production of 262Db in the 248Cm(19F,5n)262Db reaction and decay properties of262Db and 258Lr†
H. Haba,*1 M. Huang,*1 D. Kaji,*1 J. Kanaya,*1 Y. Kasamatsu,*2 Y. Kikutani,*2 H. Kikunaga,*3 Y. Komori,*2 H. Kudo,*4Y. Kudou,*1 K. Morimoto,*1 K. Morita,*1 M. Murakami,*1 K. Nakamura,*2 K. Nishio,*5 K. Ozeki,*1 R. Sakai,*1 A. Shinohara,*2T. Sumita,*1 A. Toyoshima,*5 K. Tsukada,*5 Y. Wakabayashi, *1 and A. Yoneda*1
We have been developing a gas-jet transport system
coupled to GARIS as a novel technique for superheavy
element chemistry.1) So far, isotopes of element 104, 261Rf,
and element 106, 265Sg, have been produced for chemicalstudies in the 248Cm(18O,5n) and 248Cm(22Ne,5n) reactions,respectively.1,2) In this work, we produced element 105,262
Db in the 248Cm(19F,5n) reaction and investigated its
decay properties in detail for future chemical studies of Db.
248
Cm2O3 targets with thicknesses of 230, 290, and 330
μg cm–2 were prepared by electrodeposition onto a 2-μm Tifoil. The 19F6+ or 19F9+ ion beam was extracted from RILAC.
The beam energies were 103.1 and 97.4 MeV at the middleof the target, and the typical beam intensity was 4 particle
μA. The evaporation residues (ERs) separated by GARIS
were guided into the gas-jet chamber through a0.5-μm-thick Mylar window, which was supported by a gridwith 84% transparency. Several magnetic rigidities wereinvestigated in Bρ = 1.73–2.09 Tm at a He pressure of 33Pa; the optimal collection efficiency for 262Db was 8.1 ±2.2% at Bρ = 1.89 Tm. The ERs were then transported by aHe/KCl gas jet to the rotating-wheel apparatus MANON for
α/SF spectrometry. In MANON, aerosol particles weredeposited on a Mylar foil of 0.5-μm thickness, 40 of whichwere set on the periphery of a rotating wheel. The wheel
was stepped at 15.5 s intervals to position the samples
between 15 pairs of Si PIN photodiodes.
We searched for time-correlated α1-α2 event pairs in thetime window of 58.5 s and in the energy range of 8.0 MeV≤ Eα ≤ 9.0 MeV. As a result, 71 and 4 α1-α2 pairs were foundat 103.1 and 97.4 MeV, respectively. By referring to theα-particle energies (Eα) and half-lives (T1/2) adopted for262
Db and its daughter 258Lr,3) 74 α1-α2 were reasonably
assigned to 262Db → 258Lr →. One exceptional α1-α2 pair at
103.1 MeV was 261Db → 257Lr → via the 248Cm(19F,6n)
reaction. No α1-α2 pair on 263Db produced in the248Cm(19F,4n) reaction (263Db → 259Lr →) was observed.
We also observed two SF events that correlated with the αdecays with energies and decay times of 262Db. Thissuggests that small SF and/or EC branches exist in 258Lr; the†Condensed from the article in Phys. Rev. C 89, 024618 (2014).

*1

RIKEN Nishina Center*2

Graduate School of Science, Osaka University*3

Research Center for Electron Photon Science, Tohoku University*4

Department of Chemistry, Niigata University*5

Advanced Science Research Center, JAEAEC decay daughter of 258Lr, 258No, is a short-lived SF
decaying nuclide with T1/2 ≈ 1.2 ms and bSF = 100%.3) On
the basis of the semi-empirical systematics of nuclear massand half-lives, the EC decay would be favored in 258Lr nextto the α decay.4)
The observed decay patterns of 262Db and 258Lr are shownin Fig. 1. The α-particle energies of Eα = 8.46 ± 0.04 (αintensity Iα = 70 ± 5%) and 8.68 ± 0.03 MeV (30 ± 5%)
were determined for 262Db, though three energies of Eα =8.45 (75%), 8.53 (16%), and 8.67 (9%) had been adopted.3)
The half-life of 262Db was measured to be T1/2 = 33.8+4.4–3.5 s,
and this agrees well with T1/2 = 34 ± 4 s in Ref.3) In thiswork, the SF activity with T1/2 = 30.2 ± 6.1 s was also
assigned to 262Db with a SF branch of bSF = 52 ± 4%. This islarger than the currently adopted bSF = ~33%.3) On the otherhand, the α-particle energies of 258Lr range from Eα = 8.43
to 8.73 MeV and the average α energy of Eα = 8.61 MeVagrees well with Eα = 8.605 MeV deduced from the αenergies and intensities of 258Lr in Ref.3) The half-life of258
Lr, T1/2 = 3.54+0.46–0.36 s also agrees with that in Ref.3) (T1/2= 3.9+0.4–0.3 s). The EC branch in 258Lr was first determined
to be bEC = 2.6 ± 1.8%. The cross sections for the248
Cm(19F,5n)262Db reaction were 2.1 ± 0.7 nb at 103.1 MeV
and 0.23+0.18–0.11 nb at 97.4 MeV, while those for the248
Cm(19F,4n)263Db reaction were the upper limits of ≤0.064 nb at 103.1 MeV and ≤ 0.13 nb at 97.4 MeV.
α (bα = 48%)

8.46 MeV (Iα = 70%)

262Db34 s

8.68 MeV (Iα = 30%)

EC(bEC = 2.6%)

258Lr

3.5 s

SF(bSF = 52%)258No

α (bα = 97.4%)~1.2 ms

8.565 MeV (Iα = 20%)8.595 MeV (Iα = 46%)8.621 MeV (Iα = 25%)8.654 MeV (Iα = 9%)References

SF(bSF = 100%)

Fig. 1. Observed decay
patterns for the chain
262
Db → 258Lr → (258No→).
The
α-particle
energies and intensities(Iα) of 258Lr and all decay
data of 258No are takenfrom Ref.3)1) H. Haba et al.: Chem. Lett. 38, 426 (2009).
2) H. Haba et al.: Phys. Rev. C 85, 024611 (2012).
3) R. B. Firestone and V. S. Shirley: Table of Isotopes, 8th ed.
(John Wiley & Sons, New York, 1996).
4) H. Koura: private communication.

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