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沈彩万

准裂变与融合过程的两步模型描述. 沈彩万. 湖州师范学院. 8 月 11 日 ▪ 兰州大学. 合作者： Y. Abe, D. Boilley , 沈军 杰. Content. Introduction of the model Quasi-fission stage Fusion stage Summary. Sketch map of the process. n. C. N. Reseparation (Quasi-Fission). Binary Processes (DIC). Spontaneous decays

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沈彩万

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  1. 准裂变与融合过程的两步模型描述 沈彩万 湖州师范学院 8月11日 ▪ 兰州大学 合作者：Y. Abe, D. Boilley, 沈军杰

  2. Content • Introduction of the model • Quasi-fission stage • Fusion stage • Summary

  3. Sketch map of the process n C. N. Reseparation (Quasi-Fission) Binary Processes (DIC) Spontaneous decays (a, fission) SHE

  4. Theories to describe the fusion stage • Fluctuation-Dissipation theory • DNS (di-nuclear system) model • ImQMD model • …

  5. Two-step Model including two-consecutive steps overcoming the barriers (1) Coulomb barrier; (2) Liquid drop barrier V Liquid-dropEnergy CoulombEnergy 48Ca+238U RCB = 14.14fm RC = 11.86fm RLB = 9.5fm RC R RCB RLB Pfusion = Psticking* Pform

  6. Sticking probability Psticking (a) Surface friction model (b) Empirical formula by Swiatecki [Swiatecki et al., PRC 71, 014602(2005)] • (c) Quantum tunneling • (d) …

  7. (2) Formation Probability: Pform Using liquid drop model V Ec.m. VB Coulomb Potential Liquid Drop Potential Contact Point = Rp + Rt Rc R PSticking Pform

  8. Parameters for the description of formation A2 A1 R q1 = R/R0 q2 = a p1 = pR/R0p2 = pa a: asymmetric parameter，R0:spherical radius of the compound nucleus

  9. Average value of the neck parameter

  10. Criteria for fusion hindrance in radial evolution (F.H) (no F.H.) If system evolves to spherical case: without fusion hindrance. If system evolves to two fragments: with fusion hindrance.

  11. Equation of motion for Randa Langevinequaiton:

  12. Ek=50MeV Tracks of motion with random force

  13. Ek=50MeV Formation and fragment mass-distribution initial point with pk quasi-fission formation

  14. For the fusion of heavy systems,  0 Initial radial momentum distribution at contact point According to the friction model，the relative momentums are distributed in Gaussian form：

  15. (A) Fragment massdistribution of Quasi-fission

  16. Ek=50MeV quasi-fission Probability distribution of fragment after sticking:

  17. The cross section for mass distribution of quasi-fission

  18. 238U + 26Mg Mass-distribution probability in the formation stage

  19. Exp: W.Q. Shen, PRC (1987) 238U+16O 238U+26Mg 238U+32S

  20. 238U+35Cl 238U+40Ca 238U+65Zn Properties: the larger Elab and heavier target, the wider fragment mass-distribution of quasi-fission.

  21. Heavier target, wider mass distribution Difference in the sticking stage Difference in the formation stage

  22. Larger Elab, wider mass distribution Lighter target Heavier target

  23. (B) Fusion process

  24. (1) Formation probability Ek=50MeV formation Then we get formation probability：

  25. (2) Fusion cross section • Survival Probability (statistical evaporation model) • [HIVAP program] • Residue cross section

  26. Application to the 50Ti induced reaction to synthesize SHN Key parameters: re-adjust the parameters in Swiatecki’s formula in the calculation of Psticking (DB, C) (ii) Shell correction factor fshell = 0.48

  27. Adjusting DB and C to fit experimental data The two reactions are not hindered [Gaggerler et al., Z. Phys. A 316, 291(1984)] and thus the fusion cross sections are used to adjust the parameter DB and C.

  28. Z = 120 s: ~fb Comparison with others: (a) Feng, Adamin, Nasirov, Liu, Nan Wang, Zagrebaev: ~0.1pb (b) Ning Wang et al.: ~20 fb

  29. Summary 1. The experimental data of quasi-fission is reproduced by two-step model. However more detailed aspects still should still be considered. 2. The residue cross section for 50Ti+250Cf is calculated. The predicted cross section is still far away from the current facilities. 3. Different method to calculate the capture cross section should be considered in near future.

  30. Thank you !

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