Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Measurement of barrier distribution forTi,51 V+248 Cm, and 51 V+208 Pb reactions

50T. Niwase,∗1,∗2 Y. Yamano,∗1,∗2 K. Watanabe,∗1,∗2 K. Morita,∗1,∗2 K. Fujita,∗1,∗2 T. Hirano,∗1,∗2S. Mitsuoka,∗1,∗2 K. Morimoto,∗1 D. Kaji,∗1 and H. Haba∗1Barrier distribution1–3) in a heavy-ion induced fusion reaction yields information about the nucleusnucleus interaction for the synthesis of heavy-nuclides,
especially the capture process. Comprehensive studies
on the barrier distribution, which is derived from taking the ﬁrst derivative of the quasi elastic(QE) crosssection relative to the Rutherford scattering cross section, have always been performed for several heavier
reactions.4,5) Toward future research for new superheavy elements, in this work, the QE cross-section inreactions of 50 Ti, 51 V+248 Cm and 51 V+208 Pb were investigated to understand these fusion mechanisms.
The projectiles of 50 Ti with a charge state of 11+
and 51 V charge state of 11+ were supplied by the RILAC. These ions were extracted from the 18-GHz ECRion source. A 248 Cm2 O3 target with a thickness of
210 μg/cm2 was prepared by electrodeposition onto atitanium backing foil of 0.9 mg/cm2 . A 208 Pb target of 400 μg/cm2 was prepared by vacuum evaporation on a 60 μg/cm2 carbon foil. The beam energies for the 50 Ti+248 Cm, 51 V+248 Cm and 51 V+208 Pb
measurements were 193 to 241 MeV, 194 to 247 MeV,and 176 to 224 MeV, respectively. The energy loss ofthe beam in the target was about 1 MeV. The excitation functions were obtained for steps of 2 MeV in thecenter-of-mass energy. The beam dose was monitored
by measuring the Rutherford scattered projectiles using a Si detector mounted at 45◦ with respect to thebeam axis. Target nuclides, which were recoiled out of
the target by the backward scattering (s-wave scattering), were separated in-ﬂight from projectiles and othercharged-particles using a gas-ﬁlled recoil ion separator GARIS and guided to a focal plane detection system.6) Then, the target nuclides were clearly identiﬁedby measuring the time-of-ﬂight and kinetic energy of
the recoils.
The normalized QE cross sections for the 51 V+208 Pb
reaction were obtained by assuming the ratio of thediﬀerential cross section of the QE to the Rutherford
scattering cross section ((dσ/dΩ)QE /(dσ/dΩ)R ) to be
one at suﬃciently low energy, which is shown in Fig.
1(a). The barrier distribution obtained by diﬀerentiating with respect to energy is shown in Fig. 1(b).
Comparison of the measured data with an optical potential calculation only (dashed lines) and a coupledchannel calculation (solid lines) using CCFULL software7) are shown in both ﬁgures. It was found thatthe data points are well reproduced when the coupling∗1∗2

eﬀects of the ﬁrst and second excited state of 208 Pband the second excited state of 51 V are considered in
the calculation, so excited states contributed to thesereactions.

Fig. 1. Normalized quasi-elastic cross section and barrier
distribution of the 51 V+208 Pb reaction.

The QE cross sections of the 50 Ti+248 Cm andV+248 Cm reactions are shown in Figs. 2(a) and (b),respectively. Unfortunately, we could not measure thedata in energy higher than 5.8 MeV/nucleon becauseof the lack of acceleration voltage of RILAC. In bothﬁgures, the calculations of the optical model and thecoupled channel including the coupling eﬀects of theexcited state of the target and projectiles are also given
as dashed and solid lines, respectively. However, wecannot yet discuss the channel eﬀect as nuclear deformation and excitation. Data with higher beam energies are necessary for further discussion.
51

Fig. 2. Normalized quasi-elastic cross section of the50
Ti+248 Cm (a) and 51 V+248 Cm (b) reactions.

References
1) M. V. Andres et al., Phys. Lett. B 202, 292 (1988).
2) J. R. Leigh et al., Phys. Rev. C 52, 3151 (1995).
3) H. Timmers et al., Nucl. Phys. A 584, 190 (1995).
4) S. Mitsuoka et al., Phys. Rev. Lett. 99, 182701 (2007).
5) T. Tanaka et al., RIKEN Accel. Prog. Rep. 50 (2016).
6) K. Morita et al., Eur. Phys. J. A 21, 257 (2004).
7) K. Hagino et al., Comput. Phys. Commun.123, 143(1999).

RIKEN Nishina Center
Department of Physics, Kyushu University- 69 -