RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-1. Nuclear Physics

Study of barrier distribution in the reaction 48 Ca,50 Ti+208 Pb and48
Ca+248 Cm at RIKEN-GARIS
T. Tanaka,∗1,∗2 Y. Narikiyo,∗1,∗2 K. Morita,∗1,∗2 K. Fujita,∗1,∗2 D. Kaji,∗1 K. Morimoto,∗1 S. Yamaki,∗1,∗3Y. Wakabayashi,∗1 K. Tanaka,∗1,∗4 M. Takeyama,∗1,∗5 A. Yoneda,∗1 H. Haba,∗1 K. Komori,∗1 S. Yanou,∗1B. JP. Gall,∗1,∗6 Z. Asfari,∗1,∗6 H. Faure,∗1,∗6 H. Hasebe,∗1 M. Huang,∗1 J. Kanaya,∗1 M. Murakami,∗1,∗7A. Yoshida,∗1 T. Yamaguchi,∗3 F. Tokanai,∗1,∗5 T. Yoshida,∗1,∗5 S. Yamamoto,∗1,∗2 Y. Yamano,∗1,∗2K. Watanabe,∗1,∗2 S. Ishizawa,∗1,∗5 M. Asai,∗8 R. Aono,∗7 S. Goto,∗7 K. Katori,∗1 and K. Hagino∗9In order to study the nucleus-nucleus interaction forthe synthesis of superheavy elements,1) we measured
excitation functions for the quasielastic scattering of48
Ca,50 Ti+208 Pb and 48 Ca+248 Cm. The quasielastic
scattering events were clearly separated from background events by using the gas-ﬁllled recoil ion separator GARIS and guided to focal-plane detectors.
The barrier distributions were derived by taking theﬁrst energy derivative of the excitation function. The
experimental results were well reproduced by coupledchannel calculations2) taking account of vibrational
and/or rotational excitations of nuclei and neutrontransfer before the capture process (Figs. 1 and 2).
The centroids of the barrier distributions are shownto coincide with the peak of evaporation residue crosssections for the reaction 48 Ca,50 Ti+208 Pb.3–6) This implies that, for these Pb-based cold fusion reactions, thepeak of the cross section is in good agreement with that
Ca+208Pb

0.6

0.4
Exp. data
Calculation

0.2
00.1
0.08
0.06
0.04
0.02
0Exp.
Cal.

0.15
0.1
0.05
0107
1010

Ti+208Pb

1n2n3n4n65

Exp. data
Calculation-d( dσQE/ dσR)/dE

00.2

50

0.6

0.4
0.2

10.8

dσQE / dσR

48

Exp.
Cal.

σER [pb]σER [pb]-d( dσQE/ dσR)/dE

dσQE / dσR

10.8

of the barrier distributions after one takes into accountseveral experimental conditions such as measured energy step, which is typically 2.0 MeV, and energy coverage region, which is typically 1.0 MeV, of the target
thickness.
In contrast, for the hot fusion reaction 48 Ca+248 Cm,
the peak of the cross section7,8) is shifted to the above
barrier region. The barrier distribution of the above
barrier region corresponds to side-by-side collision. In
the compound nucleus (CN) formation process, theprobability of CN formation is increased by side-byside collision because the probability depends on thedistance to the center of nuclei. It is therefore important to combine the barrier distribution study withstudies on quasi-ﬁssion and evaporation processes inorder to predict the optimum incident energy for asearch of undiscovered superheavy elements by the hotfusion reaction.

1n2n3n104
103
102104150 160 170 180 190 200

Ec.m. [MeV]

∗1
∗3
∗4
∗5
∗6
∗7
∗8
∗948

Ca+248Cm

Side-by-side collision
Deformed Target
Projectile

0.6
0.4
0.2

Exp. data
Calculation

00.08

Exp.
Cal.

0.06

V
Coulomb potential
Coulomb barrier

0.04

r0.020

Nuclear potential

101Short100 3n10-1 4nUpper limit

170 180 190 200 210 220

170 180 190 200 210

Long

Ec.m. [MeV]

Ec.m. [MeV]Fig. 2. Left side panels show same as Fig. 1. Right sidepanels show the explanation of Side-by-side collision.

Fig. 1. Measured excitation functions of quasielastic scattering cross section relative to Rutherford cross section(upper panels) and the barrier distributions (middlepanels). The lower panels show the evaporation residue
cross sections for these reactions.
∗21
0.8

References
1) S. Mitsuoka et al., Phys. Rev. Lett. 99, 182701 (2007).
2) K. Hagino et al., Comput. Phys. Commun. 123, 143(1999).
3) A. V. Belozerov et al., Eur. Phys. J. A 16, 447 (2003).
4) H. W. Gaggeler et al., Nucl. Phys. A 502c, 561 (1989).
5) Yu. Ts. Oganessian et al., Phys. Rev. C 64, 054606(2001).
6) F. P. Heßberger et al., Eur. Phys. J. A 16, 57 (2001).
7) S. Hofmann et al., Eur. Phys. J. A 48, 62 (2012).
8) Yu. Ts. Oganessian et al., Phys. Rev. C 70, 064609(2004).

RIKEN Nishina CenterKyushu University
Saitama University
Tokyo University of Science
Yamagata University
IPHC-DRS/Université de StrasbourgNiigata University
Advanced Science Research Center, JAEA
Tohoku University- 68 -