RIKEN Accel. Prog. Rep. 48 (2015)

Ⅲ-3. Radiochemistry & Nuclear Chemistry

Production of 262,263 Db in the 248 Cm(19 F,xn)267−x Db reactionsat Elab = 96 MeV
M. Murakami,∗1,∗2 S. Goto,∗1 K. Ooe,∗1 D. Sato,∗1 S. Tsuto,∗1 N. Goto,∗1 T. Koyama,∗1 R. Aono,∗1 H. Haba,∗2
M. Huang,∗2 and H. Kudo∗1∗1∗2

the daughter nuclide, T1/2 = 4.5+1.7−1.0 s, is in agreement with the reported half-life of 258 Lr, T1/2 = 3.9s.3) Thus, these events are attributed to the α deααcay chain 262 Db → 258 Lr →. The expected numberof random correlations was evaluated to be 0.3 in thisenergy region. Regarding all 14 events as true ones,
the production cross section of 262 Db is derived as σ= 0.25+0.08−0.07 nb. This cross section is consistent withthe previously reported one, σ = 0.23+0.18−0.11 nb at 97.4
MeV.1)
Only one α-α correlation was found around the energy regions of 263 Db and its α-decay daughter 259 Lr,
as shown by an arrow in Fig. 1(a). Although this number of the event, one, is comparable with the expected
number of random events, the deduced half-life of thedaughter nucleus, T1/2 = 3.1+14.8−1.4 s, is consistent withthe reported half-life of 259 Lr (T1/2 = 6.2 s3) ). If thisevent is regarded as a true one, the cross section of263
Db is deduced to be σ = 0.031+0.072−0.026 nb, which isone order of magnitude smaller than that of 262 Db as
well as the HIVAP predictions.1)

Daughter energy
energy (MeV)(MeV)
Daughter

9.09.0(a)(a)

263263262262DbDbDb
Db(c)(c)

8.8
8.8
258
258

Lr
Lr

8.6
8.6
8.4
8.4

259
259

Lr
Lr

8.2
8.2
8.0
8.0

20
202020Counts // 20
20 keVkeVCounts

The isotope 262 Db (T1/2 = 33.8 s1) ) is often usedin the chemical studies of element 105, Db. AtRIKEN, the decay properties of 262 Db produced in
the 248 Cm(19 F,5n)262 Db reaction were recently studied with a gas-jet transport system coupled to the gasfilled recoil ion separator GARIS.1) In this study, however, 263 Db produced in the 4n channel was not observed at 97.4 MeV and 103.1 MeV. The upper-limit
cross sections of 263 Db were rather smaller than thosepredicted by the HIVAP code, which reproduced the5n channel fairly well. Therefore, in this work, we investigated the production of Db isotopes at a lower
energy of 96 MeV, at which the predicted excitation
function for 263 Db exhibits the maximum.
A 248 Cm2 O3 target of 460 µg/cm2 thickness was prepared by electrodeposition onto a Be backing foil of
1.8-mg/cm2 thickness. nat Gd2 O3 of 23-µg/cm2 thickness was admixed with the target material to simultaneously produce 170 Ta (T1/2 = 6.76 min) via thenatGd(19 F,xn)170 Ta reaction. A 19 F7+ beam was supplied by the AVF cyclotron. The beam energy at themiddle of the target was 96.2 MeV, and the energy
degradation in the target was estimated to be 1.0 MeV.
The average beam intensity was 450 pnA.
The reaction products recoiling out of the target were continuously transported by a He/KCl gasjet system to the rotating wheel detection system
MANON. The transport efficiency was estimated to be74%. Other details of the measurement were similar
to those in our previous study.2)
We searched for time-correlated α-α event pairs at
the α-energy range of 8.0 ≤ Eα ≤ 9.0 MeV. On setting the time window to 25 s, 16 α-α correlations werefound. Figure 1(a) shows the two-dimensional arraysof these α-α correlations. In Fig. 1(a), 74 α-α corα
relations assigned to the decay chain 262 Db → 258 Lrα1)→ in the previous experiment are compared. Theα-particle spectra of the parent and daughter nuclides
are shown in Figs. 1(b) and (c), respectively. For theparent α spectrum, the 8.46-MeV α line of 262 Db isseen, while the 8.68-MeV α line was not very clear owing to the low counting statistics. On the other hand,the α lines of 258 Lr were clearly found in the daughter
α spectrum.
In Fig. 1(a), a solid box indicates the gated α-energy
range of the parent 262 Db (8.26–8.83 MeV) and thedaughter 258 Lr (8.36–8.80 MeV). Fourteen events arefound in this energy region. The deduced half-life of(b)(b)

ThisThis work
workHabaHaba etet al.
al. (2014)(2014)

1010001000
10Counts
Counts // 20
20 keVkeV

88

8.2
8.2

8.4
8.4

8.6
8.6

8.8
8.8

99

ParentParent energy
energy (MeV)(MeV)

Fig. 1. (a) Two-dimensional representation of timecorrelated events. (b) α spectrum of parent nuclei. (c)α spectrum of daughter nuclei.

References
1) H. Haba et al.: Phys. Rev. C 89, 024618 (2014).
2) M. Murakami et al.: RIKEN Accel. Prog. Rep. 47, 265
inpress.
(2014)
3) R. B. Firestone and V. S. Shirley: Table of Isotopes, 8thed. (John Wiley & Sons, 1996).

Department of Chemistry, Niigata University
RIKEN Nishina Center- 292 -

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