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

2 A.K. Nasirov 1,2, G. Giardina 3, A. Fukushima 4, Y. Aritomo 1,4, G. Mandaglio 3, A.I. Muminov 2, M. Ohta 4, T. Wada 4, R.K. Utamuratov 2 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-total kinetic 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. Solid line – G.G. Adamian, et al. PRC 56 (1997) 373 Long dashed -- Short dashed- - Dotted - Temperatura= 2 MeV Temperatura= 1 MeV Temperatura= 0.5 MeV By Yamaji et al(microscopic) : S. Yamaji and A. Iwamoto, Z. Phys. A 313, (1983) 161.

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

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

8 Potential energy surface for fusion of compound nucleus U dr (A, Z,, ß 1, α 1 ; ß 2, α 2 ) = B 1 + B 2 + V (A, Z, ß 1, α 1 ; ß 2, α 2 ; R) - (B C N + V C N (L )) a- entrance channel; b-fusion channel; c and d are quasifission channels

9 Potential energy surface for fusion of compound nucleus 214 Th

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 (E lab,L;  1,  2 )= (2L +1) T(E lab, L;  1,  2 ) L dyn and L min are determined by dynamics of collision and calculated by solution of equations of motion for the collision trajectory:  fus (E lab,L) =  cap (E lab,L;  1,  2 ) P CN (El ab,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) 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 16 O+ 238 U 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) Nasirov A.K. et al Nucl. Phys.A759 (2005) 342

19 Dependence of the driving potential (а) and quasifission barrier (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 216 Th: a) Capture b) Complete fusion c) Evaporation residues cross sections.

21 Driving potential U driving ( c ) for reactions 40 Ar+ 172 Hf, 86 Kr+ 130 Xe, 124 Sn+ 92 Zr leading to formation of compound nucleus 216 Th : U driving =B 1 +B 2 -B (1+2) +V( R ) Due to peculiarities of shell structure B fus (Kr) > Bfus (Kr) and, consequently,  fus (Kr+Xe) <  fus (Zr+Sn)

22 Angular momentum distribution for the complete fusion σ fus (L) (E lab ) as a function of momentum and and beam energy for reactions leading to formation of 216 Th. 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 220 Th Comparison of the fusion and evaporation residue (total neutron emissions) cross sections for the 16 O+ 204 Pb (I) and 124 Sn+ 96 Zr (II) reactions. Comparison of the fission branching ratio Γ f / Γ tot for the 16 O+ 204 Pb (red) and 124 Sn+ 96 Zr (blue) reactions G. Fazio,.., Nasirov A.K., et al. Eur. Phys. Jour. A, 2005

24 Fusion angular momentum distribution for the reaction 16 O+ 204 Pb и 96 Zr+ 124 Sn

25 Conclusions 1.An advantage of the orientation angles 60 o < α <90 o 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 48 Ca+ 249 Cf reaction