Nasirov A.K.

1. Joint Institute for Nuclear Research Flerov Laboratory of Nuclear Reactions Role of the nuclear shell structure and orientation angles of deformed reactants in complete fusion Nasirov A.K.

2. A.K. Nasirov1,2, G. Giardina3, A. Fukushima4, Y. Aritomo1,4, G. Mandaglio3, A.I. Muminov2, M. Ohta4, T. Wada4, R.K. Utamuratov2 1. Flerov Laboratory of Nuclear Reactions JINR, Dubna, Russia 2. Heavy Ion Physics Department, INP, Tashkent, Uzbekistan 3. INFN, Sezione di Catania, and Dipartimento di Fisica dell‘ Universitá di Messina, Italy 4. Department of Physics, Konan University, Kobe, Japan

3. Content • Introduction • Main mechanisms of heavy ion collisions at low energies • Dependence of capture and fusion dynamics on the mass, mass asymmetry, shape nuclei and orientation angles of their symmetry axis • Role of the peculiarities of shell structure in complete fusion • Conclusion

4. Difference between paths of the capture and deep inelastic collisions ТКЕ-totalkinetic energy V( R ) – nucleus-nucleus potential E*DNS – excitation energy of double nuclear system

5. Comparison of the friction coefficients, calculated by different methods D. H. E. Gross and H. Kalinowski, Phys. Rep. 45, (1978) 175. G.G. Adamian, et al. PRC 56 (1997) 373 Solid line – By Yamaji et al(microscopic): Long dashed-- Short dashed- - Dotted - Temperatura= 2 MeV Temperatura= 1MeV Temperatura= 0.5MeV S. Yamaji and A. Iwamoto, Z. Phys. A 313, (1983) 161.

6. Reaction mechanisms following after capture:fast-fission, quasi-fissionand fusion-fission.

7. Fast-fission of the mononucleus Lfus > L > Lfis.bar A.J. Sierk, Phys.Rev. C, 33 (1986) 2039

8. Potential energy surface for fusion of compound nucleus 284114 a- entrance channel; b-fusion channel; c and d are quasifission channels Udr (A, Z, , ß1 , α1 ; ß2 , α2 ) = B1 + B2 + V (A, Z, ß1 , α1 ; ß2 , α2 ; R) - (BC N + VC N (L ))

9. Potential energy surface for fusion of compound nucleus 214Th

10. Nucleus-nucleus potential as a function of the distance between nuclei and orientation their axial symmetry axis

11. Nucleus-nucleus interaction potential

12. Dependence of the capture and fusion cross sections on the orientation angle of the axial symmetry axis of reactants

13. Dynamics of capture of projectile by target-nucleus • cap (Elab,L; 1,2)= (2L +1) T(Elab,L;1,2) Ldyn and Lminare determined by dynamics of collision and calculated by solution of equations of motion for the collision trajectory:  fus (Elab ,L) =cap(Elab ,L; 1,2) PCN(Elab ,L; 1,2) {}

14. Partial fusion cross section as a function of the orientation of axial symmetry axis of reactants

15. Comparison of the capture and fusion excitation functions with the experimental data and Langevin calculations S. Mitsuoka, et al. PRC 62 (2000) 054603. Y. Aritomo, M. Ohta,Nucl.Phys. A744 (2004) 3

16. Quasifission cross sections as a function of the orientation angles of colliding nuclei

17. Dependence of the fusion and quasifission cross sections on the orientations of colliding nuclei Nasirov A.K. et al Nucl. Phys.A759 (2005) 342

18. Comparison capture and fusion cross sections for the 16O+238U reaction There is quasifission Hinde et al., Phys. Rev. Lett. 74 (1995) 1295 There is not quasifission K. Nishio et al., Phys.Rev.Lett. 93 (2004) 162701 Nasirov A.K. et al Nucl. Phys.A759 (2005) 342

19. Dependence of the driving potential (а) and quasifissionbarrier (b) on the mutual orientations of the axial symmetry axes of nuclei

20. The role of the entrance channel and shell structure of reactants at formation of the evaporation residues in reactions leading to the same compound nucleus 216Th:a) Capture b) Complete fusionc) Evaporation residuescross sections.

21. Driving potential Udriving( c ) for reactions 40Ar+172Hf, 86Kr+130Xe, 124Sn+92Zr leading to formation of compound nucleus216Th : fus (Kr+Xe) < fus(Zr+Sn) Due to peculiarities of shell structure Bfus (Kr) > Bfus (Kr) and, consequently, Udriving=B1+B2-B(1+2)+V( R )

22. Angular momentum distribution for the complete fusion σfus(L)(Elab) as a function of momentum and and beam energy for reactions leading to formation of 216Th. G. Fazio, et al., Journal of the Physical Society of Japan 388, 2509 (2003).

23. Effect of the entrance channel on the fission branching ratio of the excited compound nucleus 220Th Comparison of the fusion and evaporation residue (total neutron emissions) cross sections for the 16O+204Pb (I) and 124Sn+96Zr (II) reactions. Comparison of the fission branching ratio Γf / Γtot forthe 16O+204Pb (red) and 124Sn+96Zr (blue) reactions G. Fazio, .., Nasirov A.K., et al. Eur. Phys. Jour. A, 2005

24. Fusion angular momentum distribution for the reaction16O+204Pb и96Zr+124Sn

25. Conclusions • An advantage of the orientation angles 60o < α<90o for observation maximum values of fusion cross section is demonstrated by the analysis of dependence of the capture dynamics and fusion and quasifission barriers on the orientation of the axial symmetry axis of reactants. 2. The results of calculation showed that increase of beam energy leads only to involving of the larger orientation angles. If the colliding nuclei undergo the ``tip-tip" collisions only an increase of the beam energy does not lead to increase fusion cross section. 3. The angular momentum of the compound nucleus depends strongly on the dynamics of capture and peculiarities of shell structure at transformation of the dinuclear system into compound nucleus.

26. THANK YOU I am grateful to the Poland – Russian Bogoliubov - Infeld Program for the support my participation in this Workshop.

27. Evaporation residue for 48Ca+249Cf reaction