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中国原子能科学研究院 C hina I nstitute of A tomic E nergy

中国原子能科学研究院 C hina I nstitute of A tomic E nergy. 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. Outline. Angular distributions of 32 S+ 184 W system

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中国原子能科学研究院 C hina I nstitute of A tomic E nergy

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

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

  3. 1. Angular distributions of 32S+184W system Experiment was performed at the China Institute of Atomic Energy (CIAE). Ebeam = 140, 145, 150, 155, 160, 165, and 170 MeV. Si-Strip Si(Au) Experimental setup

  4. Angular distributions, fitted by • To extract c.s., K02, <l2>, and Aexp. • 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.

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

  6. Results Exist quasi-fissions to a certain extent.

  7. 2. Mass-TKE distributions of 34S+186W system Experiment was performed at the Japan Atomic Energy Agency (JAEA). Ebeam = 143, 163, 180 MeV. Forward: Si(Au) – Backward Si-strips FF = 60.63 BF = -75.39 Angle resolved Mass-TKE distributions (in 4.2 steps) More forward, more asymmetric mass distributions

  8. 34S+186W k = 0.0048 MeV/u No pronounced quasi-fission.

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

  10. 3. Mass distributions of 48Ti-induced reaction systems Experiment was performed at the Australian National University (ANU). Beam: pulsed 48Ti beam (width: 1.5 ns, interval: 106.7 ns), E = 206 - 296 MeV (  VB). Target: 144,154Sm, 162Dy, 174Yb, 186W, 192Os, 196Pt, 200Hg, and 208Pb. Measured by two MWPPACs (CUBE), covered c.m. = 40 – 140 .  50 mass-angle-distribution spectra were measured.

  11. 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.

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

  13. Dependence on fissility Minimum proportion of QF:

  14. 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 Eref: Ec.m./VB = 1.15.

  15. 4. Summary • Angular distributions of fission fragments for the 32S+184W 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 34S+186W 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 48Ti-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.

  16. 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 102413, 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 319-1195, Japan A. K. Nasirov Joint Institute for Nuclear Research, RU-141980, Dubna, Russia C. Mandaglio, M. Manganaro, and G. Giardina, Dipartimento di Fisica dell’ Universita di Messina, 98166 Messina, and Istituto Nazionale di Fisica Ncleare, Sezione di Catania, Italy

  17. Thank you !  China Institute of Atomic Energy

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