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Quasifission Reactions in Heavy Ion Collisions: Structure and Dynamics

This paper discusses the synthesis of heavy nuclei through quasifission reactions in low energy heavy ion collisions. It explores the differences between fusion-fission and quasifission mechanisms, as well as the characteristics and distributions of reaction fragments.

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Quasifission Reactions in Heavy Ion Collisions: Structure and Dynamics

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  1. “Interfacing Structure and Reaction Dynamics in the Synthesis of the Heaviest Nuclei” at the ECT*, Trento, Italy, September 1-4, 2015 Quasifission reactions in heavy ion collisions at low energies A.K. Nasirov1, 2 1Joint Institute for Nuclear Research, 141980 Dubna, Russia 2Institute of Nuclear Physics, 100214, Tashkent, Uzbekistan September 1, 2015 Trento

  2. Synthesis of superheavy elements in the cold and hot fusion reactions.

  3. Quasifission is a binary process producing two reaction products in heavy ion collisions. The basic difference between fusion fission and quasifission is that compound nucleus formation is not achieved in the latter mechanism. Quasifission can be thought of as a bridge between deep-inelastic scattering, where the relative kinetic energy between the fragments can be partially damped, but the mass asymmetry of the entrance channel is mostly preserved, and compound nucleus fission reactions.

  4. Comparison of characteristics of reaction fragments

  5. Reaction channels in heavy ion collisions at low energies (E) Complete fusion (Superheavy element)

  6. Dependence of the formation of fission-like binary fragments on the orbital angular momentum, L L=Iω Fast fission 0 < L < LB 0 < L < Lcap LB < L < Lcap

  7. Mass-energetic distribution of the binary products in heavy ion collisions Quasifission Deep inelastic collisions Fusion-fission

  8. Mechanisms of the reaction following after capture (capture means formation of dinuclear system): Fusion-fission, quasifission and fast-fission.

  9. Progress in study of the quasifission reactions Phys.Rev.Lett. 36, 18 (1976) The mass distribution of the quasifission products is peaked near the masses of the target and of the projectile. The fraction of the mass distribution located at symmetry is relatively small. The fragment kinetic energies are characteristic of the Coulomb repulsion of fission fragments. The angular distributions are peaked in the vicinity of the grazing angle.

  10. Full damped (capture) and partially damped (deep-inelastic collision) events. diffusion effects on nucleons angular dependence of energy loss

  11. Mass-angle distribution as function of the beam energy in 63Cu+197Au reaction. C. Ngô et al, Nucl.Phys. A267, 181 (1976). The increase of the beam energy leads to the shift of the mass distribution of the reaction products to the small angles.

  12. α=M1 t is maximum of the mass distribution as a function of time ; Γ2 is the square of the width (FWHM) related with diffusion coefficient.

  13. What is questionable in fusion-fission reactions ? Dynamics of complete fusion and a role of the entrance channel in formation of reaction products in heavy ion collisions are questionable or they have different interpretation still now. For example, -- what kind of fusion mechanism makes a main contribution to the formation of compound nucleus: the increase of the neck between interacting nucleus, or multinucleon transfer at relatively restricted neck size, or + ? The details of angular momentum distribution of dinuclear system and compound nucleus those determine cross sections of evaporation residue, fusion-fission and quasifission products; The theoretical and experimental studies are important in order to clarify the origin of fission events (CN-fission against quasifission), namely, to separate fusion-fission fragments from the quasifission and fast-fission products.

  14. Beam I. Deep inelastic collisions: Partial momentum transfer; There is not equilibrium of energy distribution and mass distribution; Anisotropic angular distribution b Formation of the dinuclear system (Capture reactions) Beam II. Quasifission: 1) Full momentum transfer; 2) Equilibrium of energy distribution and mass distribution; 3) Anisotropic and isotropic angular distributions. b Beam III. Compound nucleus formation: 1) Full momentum transfer; 2) Equilibrium of energy distribution and mass distribution; 3) Isotropic angular distributions. ` b

  15. Interpretation ofthemechanismofproductionradioisotopes with different energy at SHIP 64Ni + 207Pb S. Heinz, V. Comas, F. P. Heßberger, S. Hofmann, D. Ackermann, et al. Eur. Phys. Jour. A 38, 227 (2008) “Di-nuclear systems studied with the velocity filter SHIP” Mass – charge and angular distributions of the multinucleon transfer reaction were estimated.

  16. The role of nuclear shell effects in the yield of the quasifission products.

  17. Mixing of the distribution of fragment masses versus total kinetic energy DIC 70Zn DIC QF QF FF DIC QF DIC DIC FF QF QF DIC Experimental data from Ref. W.Q. Shen et al (GSI) Phys.Rev.C36, 115 (1987), where two reaction products of deep-inelastic collisions (DIC), quasifission (QF) and fusion-fission (FF) processes are registered for three reactions at three values of beam energy 5.4, 6.7, 7.5 MeV A.

  18. А – deep inelastic collision products Mixing products formed in the deep-inelastic collisions and quasifission В- quasifission products G. Fazio et al.,Mod. Phys. Lett. Vol. 20, No. 6 (2005) 391 Z Z Z2=82 Z1=20

  19. Comparison of theoretical results with the experimental data for the capture, fusion and evaporation residue excitation functions G. Fazio, et al. Modern Phys. Lett. A 20, No. 6 (2005) 391-405

  20. The observeddecreaseofthequasifissioncontributionbyincreaseofthecollisionenergy in 48Ca+154Smreaction. (frompaperKnyazhevaG.N. et al. Phys. Rev. C 75, 064602(2007).

  21. Evolution of the mass distributioin of quasifission fragments

  22. TKE=K1+K2 P(M1,M2.TKE) P(M1,M2)= Σ P(M1,M2.TKE) <TKE>= Σ TKE P(M1,M2.TKE)

  23. Explanation of the lack of quasifission fragment yields at the expected place of mass distribution in the 48Ca+144Smreaction

  24. Comparison of the capture, fusion-fission and quasifission cross sections obtained in this work with data from experiments KnyazhevaG.N. et al. Phys. Rev. C 2007. Vol. 75. –P. 064602(13). and evaporation residues StefaniniA.M. et al. Eur. Phys. J. A –2005. Vol. 23. –P.473

  25. The role of the angular momentum of dinuclear system in competition between complete fusion and quasifission.

  26. The lifetime and rotational angle of the dinuclear system formed in 48Ca+154Sm reaction as a function of the Ec.m. energy.

  27. The overlap of the angular momentum distributions of the fusion-fission and quasifission processes.

  28. Comparison of the potential wells of the nucleus-nucleus interaction for reactions leading to formation of 220Th. Bqf

  29. Importance of the radial and tangential friction coefficients

  30. A new problem in separation of fusion-fission and the quasifission products in heavy ion collisions when there is overlap their mass and angular distributions. The partial quasifission excitation function calculated at different values of the collision energy Ec.m. for the 32S + 184W reaction.

  31. The analysis of experimental data deals with the limiting value of angular momentum lCN for complete fusion, as in paper by R.S. Naik et al. Phys. Rev. C 76, 054604 (2007). • The use of this formula assumes that the quasifission products are not formed in collisions with angular momentum L < LCN.

  32. The methods of calculation of the capture and fusion cross section in the dinuclear system approach. Main assumptions: the shell effects does not allow to fuse nuclei immediately; the hindrance to fusion is determined by the intrinsic fusion barrier which is determined from the landscape of the potential energy surface of dinuclear system; the interacting nuclei can be deformed and nucleon exchange between them takes place allowing dinuclear system to be transformed into compound nucleus or to populate shapes corresponding minimal values of the potential energy surface (superdeformed shapes and shapes preceding to quasifission); 4) The lifetime τDNSof dinuclear system is determined by its excitation energy and quasifission barrier Bqf.

  33. The evaporation residue cross section (synthesis of superheavy element) is calculated by the well known expression: is fusion probability which calculated by the methods of dinuclear system concept N.A. Antonenko et al., Phys. Lett. B 319, 425 (1993);Phys. Rev. C 51, 2635 (1995); G. Adamian, N.V. Antonenko, and W. Scheid, Eur. Phys. J. A 41, 235 (2009); A. K. Nasirov et al. Phys. Rev. C 79, 024606 (2009). is capture probability, which calculated in different theoretical models by different way. A. K. Nasirov et al., Nucl. Phys.A759, 342 (2005). K. Kim et al., Phys.Rev. C 91, 064608 (2015).

  34. Equations of motion used to find the capture of projectile by target-nucleus

  35. Nucleus-nucleus interaction potential

  36. G.G. Adamian, et al. Phys. Rev. C56 No.2, (1997) p.373-380 A.K. Nasirov, Thesis of the Doctor of Science, 2004, Institute of Nuclear Physics, Tashkent Hamiltonian for calculation of the transport coefficients of collective motion

  37. Density dependent effective nucleon-nucleon forces The values of the constants of the effective nucleon-nucleon forces from the textbook A.B. Migdal, “Theory of the Finite Fermi-Systems and properties of Atomic Nuclei”, Moscow, Nauka, 1983. The constants of version II were used in our calculations.

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

  39. Calculation of the competition between complete fusion and quasifission: Pcn(EDNS,L) Nasirov A.K. et al. Nuclear Physics A 759 (2005) 342–369 Fazio G. et al, Modern Phys. Lett. A 20 (2005) p.391

  40. G.G. Adamian, et al. Phys. Rev. C53, (1996) p.871-879 R.V. Jolos et al., Eur. Phys. J. A 8, 115–124 (2000) Nucleon transfer coefficients for evolution of the charge asymmetry of dinuclear system

  41. A new problem in separation of fusion-fission and the quasifission products in heavy ion collisions when there is overlap their mass and angular distributions. The partial quasifission excitation function calculated at different values of the collision energy Ec.m. for the 32S + 184W reaction.

  42. Comparison of the partial fusion cross sections of the 40Ar+180Hf and 82Se+138Ba reactions leading to the same compound nucleus 220Th K. Kim et al. Phys.Rev.C 91, 064608 (2015) (b) (a) (d) (c)

  43. Fusion hindrance increases by increasing the orbital angular momentum. Dependence of the driving potential and quasifission barrier on the angular momentum of dinuclear system formed in reactions leading to formation of compound nucleus 216Th. PHYSICAL REVIEW C 72, 064614 (2005) • F Udr = B1 + B2 - (BCN + VCN (L )) + V (A, Z, ß1 , α1 ; ß2 , α2 ; R,L)

  44. Calculation of the life time of dinuclear system

  45. Collective enhancement of level density of DNS

  46. Description of the observed angular anisotropy of the fissionlike products.

  47. Estimation of the quasifission contribution in the observed angular anisotropy of the fissionlike products. B.B. Back et al, Phys. Rev.Lett. 50, 818 (1983) B. John, S.K. Kataria, Phys.Rev.C 57, 1337 (1998) A.K. Nasirov, et al. Eur. Phys. J. A 34, 3 25–339 (2007)

  48. Statistical calculation of the anisotropy of the angular distribution A.K. Nasirov, et al. Eur. Phys. J. A 34, 325–339 (2007)

  49. Partial fusion cross section as a function of the orientation of axial symmetry axis reactants Nasirov A.K. et al. The role of orientation of nuclei symmetry axis in fusion dynamics, Nucl. Phys. A 759 (2005) 342

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