Fusion-Fissions and Quasi-fissions of 32,34 S- and 48 Ti-induced Fissions at Near-barrier Energies H. Q. Zhang China Institute of Atomic Energy 中国原子能科学研究院 China Institute of Atomic Energy

Outline 1.Angular distributions of 32 S+ 184 W system 2.Mass-TKE distributions of 34 S+ 186 W System 3.Mass distributions of 48 Ti-induced reaction systems 4.Summary

1. Angular distributions of 32 S+ 184 W system Experiment was performed at the C hina I nstitute of A tomic E nergy (CIAE). E beam = 140, 145, 150, 155, 160, 165, and 170 MeV. Si-Strip Si(Au) Experimental setup

Angular distributions, fitted by  To extract c.s., K 0 2,, and A exp.  To compare with the calculations of di-nuclear system (DNS) model.  To understand the dynamic processes of capture, fusion, fast-fission, quas-ifission, fusion-fission, and evaporation residue.

216 Th Potential-energy surface 15  45  Orientation dependent driving-potential DNS model

Results Exist quasi-fissions to a certain extent.

2. Mass-TKE distributions of 34 S+ 186 W system Experiment was performed at the J apan A tomic E nergy A gency (JAEA). E beam = 143, 163, 180 MeV.Forward: Si(Au) – Backward Si-strips  FF =   BF =  Angle resolved Mass-TKE distributions (in 4.2  steps) More forward, more asymmetric mass distributions

k = MeV/u 34 S+ 186 W No pronounced quasi-fission.

Conclusion: 1)No pronounced quasi-fission components are observed in the mass distributions, but 2)Pronounced quasi-fission components are observed in the angular distributions, and 3)Anisotropies can be explained by pre-equilibrium mode. Relaxation time of K > relaxation time of mass

3. Mass distributions of 48 Ti-induced reaction systems Experiment was performed at the A ustralian N ational U niversity (ANU). Beam: pulsed 48 Ti beam (width: 1.5 ns, interval: ns), E = MeV (  V B ). Target: 144,154 Sm, 162 Dy, 174 Yb, 186 W, 192 Os, 196 Pt, 200 Hg, and 208 Pb. Measured by two MWPPACs (CUBE), covered  c.m. = 40  – 140 .  50 mass-angle-distribution spectra were measured.

Mass widths depend on excitation energies compound saddle-point scission-point Systematic tendency: Differences in lighter and heavier, as well as in spherical and deformed targets.

Dependence on reaction energy Importance of target deformation & fissility of composite nucleus.

Dependence on fissility Minimum proportion of QF:

Dependence on deformation Mass distributions are broadened by quasi-fissions induced by the tip collisions at low energies for the deformed targets, while such orientation effects vanish at high energies. And this effects can be estimated by an so-called enhancement factor: where E ref : E c.m. /V B = 1.15.

4. Summary  Angular distributions of fission fragments for the 32 S+ 184 W system have been measured at 7 energies. The quasi-fission components are observed and can be explained by the DNS model.  Mass-TKE distributions of fission fragments for the 34 S+ 186 W system have been measured at 3 energies. No pronounced quasi-fission components are observed and in agreement with the scission-point statistical calculations.  K pre-equilibrium fission may occur in the S+W systems, which requires the detail Mass-TKE-Angle correlated measurements (MEADs).  Systematic tendencies of mass distributions have been explored for the 48 Ti-induced fissions at near-barrier energies. The observed behavior is a complex function of the fissility, deformation, and reaction energy. The quasi-fission induced by the orientation effects may be reduced for the targets with large deformations.

Thanks to all the collaborators: C. J. Lin, F. Yang, C. L. Zhang, Z. H. Liu, H. M. Jia, X. X. Xu, L. Yang, P. F. Bao, and L. J. Sun China Institute of Atomic Energy, P. O. Box 275 (10),Beijing , China R. du Rietz, D. J. Hinde, M. Dasgupta, R. G. Thomas, M. L. Brown, M. Evers, L. R. Gasques, and M. D. Rodriguez Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia H. Ikezoe, K. Nishio, S. Mitsuoka, and K. Satou Japan Atomic Energy Agency, Tokai, Ibaraki , Japan A. K. Nasirov Joint Institute for Nuclear Research, RU , Dubna, Russia C. Mandaglio, M. Manganaro, and G. Giardina, Dipartimento di Fisica dell’ Universita di Messina, Messina, and Istituto Nazionale di Fisica Ncleare, Sezione di Catania, Italy

Thank you ! China Institute of Atomic Energy