Journal of Nuclear and Radiochemical Sciences,Vol. 3, No. 1, pp. 85–88, 2002

85

Production Cross Sections of 261 Rf and 262 Db in Bombardments of 248 Cm with 18 O and 19 F
IonsY. Nagame,∗,a M. Asai,a H. Haba,a S. Goto,b K. Tsukada,a I. Nishinaka,a K. Nishio,a S. Ichikawa,aA. Toyoshima,a K. Akiyama,a H. Nakahara,a M. Sakama,c M. Schädel,d J. V. Kratz,eH. W. Gäggeler,f and A. Türlerg
aJapan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japanb
Department of Chemistry, Niigata University, Niigata 950-2181, Japanc
Department of Radiological Technology, University of Tokushima, Tokushima 770-8509, Japan
dGesellschaft für Schwerionenforschung, D-64291 Darmstadt, Germany
eInstitut für Kernchemie, Universität Mainz, D-55099 Mainz, Germanyf
Universität Bern, CH-3012 Bern, Switzerland
gPaul Scherrer Institut, CH-5232 Villigen, Switzerland
Received: February 28, 2002; In Final Form: April 4, 2002
The transactinide nuclei, 261 Rf and 262 Db, have been produced in the 248 Cm(18 O, 5n) reaction at beam energies of91, 94, and 99 MeV, and in the 248 Cm(19 F, 5n) reaction at 106 MeV, respectively. The production cross sections areevaluated from the mother-daughter correlations of α energies between 261 Rf and 257 No, and 262 Db and 258 Lr. Themaximum cross section of the 248 Cm(18 O, 5n) reaction is measured to be 13 ± 3 nb at around 94 MeV, while theproduction cross section of 262 Db in 248 Cm(19 F, 5n) is 1.3 ± 0.4 nb at 106 MeV.
1. Introduction
For chemical studies of element 104, 78-s 261 Rf produced inthe 248 Cm(18 O, 5n) reaction at 97 MeV with a cross section of
5 nb1 has been used. The relative maximum cross section in theabove reaction, however, was obtained at the vicinity of 95-MeV
18O bombarding energy.2 On the other hand, the cross section of<0.9 nb at 94.2 MeV has been recently measured.3 In the chemical study of element 105, 34-s 262 Db and partially 27-s 263 Db
produced in the 5n- and 4n reactions of 18 O with 249 Bk targets
with cross sections of 6 nb and 2 nb,4 respectively, are used, although the target material 249 Bk is very rare and highly radioactive with the half-life of 320 d. Thus the other reaction path248Cm(19 F, 5n) producing 262 Db has been studied as a possible
alternative. Recently, the production cross section at a beam energy of 106.5 MeV has been measured to be 0.26 nb by Dressler
et al.,5 which is more than one order of magnitude smaller thanthat in the 249 Bk(18 O, 5n)262 Db reaction,4 while Naour et al. havereported the relatively large cross section value of about 2 nb inthe same reaction.6
In the present study, to evaluate the optimum irradiation condition for the production of 261 Rf through the 248 Cm(18 O, 5n) reaction, the production cross sections at 91, 94, and 99 MeV aremeasured. We also determine the accurate production cross section of 262 Db in the bombardment of 248 Cm with the 106-MeV
19F beam.
2. Experimental Procedures
A schematic of the experimental setup including a target andrecoil chamber arrangement and a rotating wheel detection system is shown in Figure 1. The 248 Cm target of 590 µg/cm2thickness and 5 mm diameter was prepared by electrodeposition onto a 2.2 mg/cm2 thick Be backing foil. The 18 O6+ and19 7+
F beams from the JAERI tandem accelerator passed througha 2.0 mg/cm2 HAVAR entrance window, 0.09 mg/cm2 He cooling gas, and the 2.2 mg/cm2 Be target backing before entering
the target material. The beam current of each ion was approximately 250–300 particle nA.
The reaction products recoiling out of the target were stopped
and thermalized in a volume of He gas (about 1 bar) which had
been loaded with KCl aerosols generated by sublimation from∗Corresponding author.

FAX: +81-29-282-5927.

E-mail: nagame@popsvr.tokai.jaeri.go.jp.

the surface of KCl powder at 620 ◦ C. The products attached tothe aerosols were swept out of the recoil chamber with the Hegas (2.0 L/min) and were transported through a Teflon capillary(2.0 mm i.d.) to the rotating wheel detection system MANON(Measurement system for Alpha-particle and spontaneous fissioN events ON line), where they were deposited on polyethylene terephthalate foils of 120 µg/cm2 thickness and 20 mm diameter at the periphery of an 80-position stainless steel wheel of80 cm diameter. The wheel was periodically rotated to position
the foils between six pairs of Si PIN photodiodes for α-particle
detection. Each detector had an active area of 18 ×18 mm2 . The
detection efficiency of approximately 40% for α particles wasachieved. The energy resolution (FWHM) was about 30 keV for
the top detectors and was 100 keV for the bottom ones.
To determine the gas-jet transport yield, we first collected
He Cooling Gas
248 Cm Target on Be Backing

Gas-jet Outlet
18O and 19 F Beams

Water Cooled
Beam StopHAVAR Window
2.0 mg/cm2Recoils

Gas-jet Inlet(He/KCl)

Wheel Rotation
Si PIN Photodiodes
Catcher Foil
120 µg/cm2 , 20 mm i.d.

Figure 1. Schematic of the experiment for the production of 261 Rf and262
Db.

c 2002 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 6/30/2002

J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

NagamePo212m

Po211m

5At +211m
Po

Lr
258

214m

Db +258

α

Lr
3.9 s

214

262

PoPo213AtFr

218

20212mPo217αDb34 s

Po262

Rn211m

211m

At +215

Fr218mFr1030At +αNo25 s

Po

154025726120(b)215Rf +257αRf78 sFrNo211m(a)218Counts per 20 keV

25Counts per 20 keV

Po50261211m

30218m86

100078910111278

α-Energy / MeV

9101112

α-Energy / MeVFigure 2. (a) Sum of α-particle spectra measured in the bombardment of the 248 Cm target with 94 MeV 18 O ions, and (b) that with 106-MeV 19 F ions.
TABLE 1: Experimental production cross sections of 261 Rf andDb produced in the 248 Cm(18 O, 5n) and 248 Cm(19 F, 5n) reactions,respectively, and those in the other reactions.

ReactionCm(18 O, 5n)261 Rf
248
Cm(18 O, 5n)261 Rf
248
Cm(18 O, 5n)261 Rf
248
Cm(18 O, 5n)261 Rf
248
Cm(18 O, 5n)261 Rf
248
Cm(18 O, 5n)261 Rf
248
Cm(18 O, 5n)261 Rf
244
Pu(22 Ne, 5n)261 Rf
244
Pu(22 Ne, 5n)261 Rf
248
Cm(19 F, 5n)262 Db
248Cm(19 F, 5n)262 Db
248
Cm(19 F, 5n)262 Db
249
Bk(18 O, 5n)262 Db
248

Elab / MeV
9794.2100.4
103.9919499
114120106.510610699

σ / nb5<0.94.5+3.5−2.0
1.7+3.3−1.08±2
13 ± 38±24.4
3.8
0.26+0.15−0.09
2
1.3 ± 0.4
6±3Reference
1333
Present
Present
Present
161656
Present4

the recoil of 252 Md (T1/2 = 2.3 min) produced in the reaction
238
U(19 F, 5n)252 Md behind the target in an Al catcher foil to geta reference value (100%), while 252 Md transported in the jet wascollected on a glass filter. 252 Fm (T1/2 = 25 h), the EC decaydaughter of 252 Md, in both samples was chemically separated
and subjected to α spectrometry. By comparing the production
rate measured after transport through the jet with the absolute
production rate from the catcher foil, the transport efficiency
was determined to be approximately 35%. The production crosssections were evaluated from the mother-daughter (α-α) correlations for 261 Rf–257 No and 262 Db–258 Lr.
3. Results and Discussion
The sum of α-particle spectra measured in the six top detectors for the production of 261 Rf at 94 MeV is shown in Figure 2(a). In the α-energy range of 8.10–8.40 MeV, α lines from78-s 261 Rf (8.28 MeV) and its daughter 26-s 257 No (8.22, 8.27,and 8.32 MeV) are clearly seen. No contributions from othernuclides in this energy window are observed, although there exist several α lines originating from the transfer reaction products
from the Pb impurity in the 248 Cm target. A total of 166 eventswere registered both in the top and bottom detectors in the singles measurement and 57 α-α correlation events were detected
at 94 MeV. Assuming a 100% α-decay branch (Iα ) for both 261 Rfand 257 No, the production cross sections of 261 Rf in this reaction
were evaluated to be 8 ± 2, 13 ± 3, and 8 ± 2 nb at the 18 O beamenergies of 91, 94, and 99 MeV, respectively, as shown in Table 1. The contribution of the direct production of 257 No via the248
Cm(18 O, α5n) reaction is assumed to be negligible in the studied energy region. The present cross section values are in good

Cross section / nb262101

100

Present work
Ghiorso et al. [1]Silva et al. [2]Dressler et al. [3]10-1859095

100105110

Energy / MeV
Figure 3. Cross sections of the 248 Cm(18 O, 5n)261 Rf reaction as a function of the 18 O bombarding energy. The data taken from the literature1–3
are also shown.

agreement with that of about 5 nb at around 97 MeV by Ghiorso
et al.1
Figure 2(b) shows the sum of α-particle spectra measured in
the six top detectors in the 106 MeV 19 F-induced reaction of248Cm. The α lines corresponding to those of 34-s 262 Db and its
daughter 3.9-s 258 Lr are observed. 19 mother-daughter correlations of α energies between 262 Db (8.45, 8.53, and 8.67 MeV)
and 258 Lr (8.565, 8.595, 8.621, and 8.654 MeV) were detected.
With assumption of Iα = 64% in 262 Db and Iα = 100% in 258 Lr(Ref. 7), the production cross section of 262 Db was evaluatedto be 1.3 ± 0.4 nb. The present cross section value is larger by afactor of about 6 than that by Dressler et al.,5 while that is nearly
equal to the value of about 2 nb reported by Naour et al.6
In Figure 3, the measured cross sections are plotted as a function of the 18 O bombarding energy together with the literature
data,1–3 where the relative cross section values in Reference 2
are normalized to the present results. The data except for thevalue <0.9 nb at 94.2 MeV in Reference 3 are smoothly connected with the maximum cross section of about 13 nb at around
94 MeV and show a slight tail in the energy region beyond
100 MeV.
The experimental cross sections were compared with those
expected from statistical model calculations with the HIVAP
code8 which has been modified for the calculations of fusioncross sections.9 The coupled channel method with the CCDEF
code10 was used for the calculation of the fusion cross sections,in which the influence of the static deformation of the colliding nuclei as well as the inelastic coupling to collective excited

Production Cross Sections of 261 Rf and 262 Db

J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

levels was considered. In the present calculations, the deformation of β2 and β4 11 of the 248 Cm nucleus was taken into accountand the inelastic coupling to the 2+ and 3− states of 18 O, and tothat of 3− in 248 Cm were considered. No coupling calculationsfor 19 F were performed. The fusion cross section values wereinput to the HIVAP calculations as were the initial spin distributions of the compound nucleus. The evaporation residue crosssections were calculated by the conventional Γn /Γ f competition
method, where Γn and Γ f mean the decay widths for neutron
evaporation and fission, respectively. A brief description for thedeexcitation process is given in the following. The level density
at the ground state as well as the saddle point state for a given
excitation energy E was calculated by
ρ(E) = Kvib Krot ρint (E),(1)where Kvib and Krot are the coefficients for rotational and vibrational enhancements of non-collective internal nuclear excitations ρint (E).12 To evaluate Kvib and Krot , the ground state
quadrupole deformation β2 was taken from Reference 11, while
the saddle-point deformation was from Reference 13 in thepresent calculations. The fission barrier height B f was given by
BRLDM − δW , where the rotating liquid drop fission barrier BRLDM
was obtained from Reference 13. The shell correction energy
δW was calculated as, δW = Mexp − MLDM using the experimental masses Mexp 14 and the liquid drop model masses MLDM .15
The maximum cross section of 10 nb at 96 MeV wascalculated with the statistical model HIVAP code for the248
Cm(18 O, 5n) reaction, while the calculated cross section in248
Cm(19 F, 5n) was 1.5 nb at 106 MeV, indicating that good
agreement with the present experimental values was obtainedin both reactions.
Table 1 summarizes the experimental production cross sections of 261 Rf and 262 Db together with the reference values.1, 3–6, 16In the case of the production of 261 Rf, the cross section in the248Cm(18 O, 5n) reaction is larger by a factor of 3 than that in244
Pu(22 Ne, 5n),16 while the production cross section of 262 Db in
the 249 Bk(18 O, 5n) reaction4 is larger than that in 248 Cm(19 F, 5n).
It is clear that the more mass-asymmetric reaction system gives
the larger production cross section.
In Figure 4, the cross sections observed in the 248 Cm(HI, 5n)reactions are plotted as a function of atomic number of the products. The literature values are taken from 248 Cm(12,13 C, 5n),17248Cm(15 N, 5n),18 248 Cm(18 O, 5n),1 248 Cm(19 F, 5n),5, 6 and248Cm(22 Ne, 5n).19 The decrease of the cross section withincreasing atomic number is obvious. The extrapolation of theproduction cross section for element 108, 269 Hs produced in the248Cm(26 Mg, 5n) reaction, gives approximately a few pb.
103

σ(5n) / nb

102

101

100

10-1101

102

103

104

105

106

107

ZCN
Figure 4.
Cross sections for heavy elements produced in the248Cm(HI, 5n) reactions. The present results together with those for the248Cm(12,13 C, 5n),17 248 Cm(15 N, 5n),18 248 Cm(18 O, 5n),1 248 Cm(19 F, 5n),5, 6248Cm(22 Ne, 5n)19 reactions are shown.

87

4. Conclusions
The transactinide nuclei, 261 Rf and 262 Db, were produced inthe 248 Cm(18 O, 5n) reaction at 91, 94, and 99 MeV, and in the248Cm(19 F, 5n) reaction at 106 MeV, respectively. The newly developed rotating wheel detection system, MANON, was usedto detect α-α correlations between 261 Rf and 257 No, and 262 Dband 258 Lr. The production cross section of 261 Rf was determined to be 13 ± 3 nb at 94 MeV, while that of 262 Db was
1.3 ± 0.4 nb. The statistical model calculations coupled with thecoupled channel code CCDEF taking into account the deformation of the colliding nuclei as well as the coupling to the inelastic
channels well reproduced the experimental cross sections.
Acknowledgement. The authors would like to acknowledge
the crew of the JAERI tandem accelerator for providing the 18 O
and 19 F beams. This work was partly supported by the programon the JAERI tandem accelerator collaboration and that on the
Scientific Cooperation between JAERI and GSI in Research andDevelopment in the Field of Ion Beam Application.
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