Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 47 (2014)

Cross-section measurement of the 248 Cm(19 F,5n)262 Db reaction
M. Murakami,∗1,∗2 S. Goto,∗1 K. Ooe,∗1 S. Tsuto,∗1 R. Aono,∗1 H. Haba,∗2 M. Huang,∗2 J. Kanaya,∗2S. Shibata,∗2 and H. Kudo∗1∗1∗2

Department of Chemistry, Niigata University
RIKEN Nishina Center- 265 -of the Mylar foil in MANON. After the aerosol collection, the wheel was stepped at 20-s nominal interval
to move the foils between the detector pair. Because
the long-lived activities were accumulated during theirradiation, the wheels containing the Mylar foils werereplaced every 6 h. While exchanging the wheels, theaerosols were collected on the glass filters in the collection chamber, and the glass filters were subjectedto γ-ray spectrometry to verify whether the yields of170
Ta were stable.
Figure 1 shows the sum of the measured α-spectrain the 2nd–7th top detectors, corresponding to a timeinterval of 20–140 s. A beam dose of 1.91 × 1017 wasaccumulated. In Fig. 1, α events of 262 Db (α branchbα = 48%, α energies Eα = 8.46 MeV (70%) and 8.68
MeV (30%)1) ) and its daughter nuclide 258 Lr (T1/2 =3.9 s, bα = 97.4%, Eα = 8.565, 8.595, 8.621, and 8.654
MeV5) ) are clearly recognized. However, α lines ofby-products such as Po isotopes are also observed inthe α-energy region of 262 Db and 258 Lr. Analyses of
the time-correlated α-α pairs are needed to extract theααdecay chains of 262 Db → 258 Lr →. Further analyses ofthe obtained data are in progress.
Po
7.275
211m
254
7.995
Po7.150, 7.192 Fm
215
8.026 At
214
213
7.687
Po8.375 Po
7.741 217Rn
262
8.46, 8.68 Db
258
8.565, 8.595, 8.621 Lr
211m
8.883
Po50

100

78910
Energy (MeV)

212m

20

11.660

30

Po

211m

40
Counts / 20 keV

The isotope 262 Db (T1/2 = 33.8 s1) ) is used in thechemical studies of element 105, Db. One of the commonly used direct synthetic routes of 262 Db is the reaction of 19 F with 248 Cm. Few cross sections are available for this reaction, but there is a large discrepancy
among these data. Dressler et al.2) reported a production cross section of 0.26+0.15−0.09 nb at 106.5 MeV.
3)
Nagame et al. reported a cross section of 1.3 ± 0.4 nb
at nearly the same energy, 106 MeV. The same groupalso reported a maximum cross section of 1.5 ± 0.4 nb
at 103 MeV.4) Thus, the cross-section data are inadequate, and the optimal beam energy to produce 262 Db
is not clear. Therefore, we plan to measure the excitation function of the 248 Cm(19 F,5n)262 Db reactionto effectively produce 262 Db for the future chemical
experiments of Db. First, in this work, we produced262
Db at 102 MeV.
A 248 Cm2 O3 target of 460-µg/cm2 thickness and 9mm diameter was prepared by electrodeposition onto
a Be foil of 1.8-mg/cm2 thickness. nat Gd2 O3 of 23µg/cm2 thickness was admixed with the target material to simultaneously produce 170 Ta (T1/2 = 6.76min) via the nat Gd(19 F,xn)170 Ta reaction. A 19 F7+beam of 124.9 MeV supplied by the AVF cyclotron
was passed through a 3.2-mg/cm2 Be vacuum window,
0.10 mg/cm2 of He cooling gas, and the Be backing
foil before it entered the target. The primary beamenergy was measured using time-of-flight apparatus.
The beam energy at the middle of the target was 101.9
MeV, and the energy degradation in the target was estimated to be 1.0 MeV. The average beam intensity
was approximately 440 pnA.
The reaction products recoiling out of the target
were stopped in 102.0-kPa He gas in the recoil chamber, attached to KCl aerosols generated by sublimation of KCl powder at 640◦ C, and continuously transported with a flow rate of 2.5 L/min to the rotating
wheel detection system MANON (Measurement system for Alpha-particle and spontaneous fissioN ONline) through a 8.6-m Teflon capillary with 1.59-mm
inner diameter. MANON has 7 pairs of Si PIN photodiodes, and the counting efficiency of each photodiodewas 38%. In MANON, the aerosols were deposited onMylar foils of 0.5-µm thickness, 40 of which were seton the periphery of a rotating wheel 420 mm in diameter. The gas-jet transport efficiency was estimatedto be 53.5 ± 2.0% by comparing the collected yields of170
Ta on the 10-µm Be catcher foil placed immediately
behind the target and on the Al foil set to the position

1112Fig. 1. Sum of α spectra measured in the 2nd–7th top detectors of MANON.

References
1) H. Haba et al.: In this report.
2) R. Dressler et al.: Phys. Rev. C 59, 3433 (1999).
3) Y. Nagame et al.: J. Nucl. Radiochem. Sci. 3, 85 (2002).
4) K. Tsukada et al.: Radiochim. Acta 97, 83 (2009).
5) R. B. Firestone and V. S. Shirley: Table of Isotopes, 8thed. (John Wiley & Sons, 1996).