The quasifission in heavy fusing reaction systems

1. The quasifission in heavy fusing reaction systems Junqing Li (李君清) School of Nuclear Science and Technology Lanzhou University Institute of Modern Physics, Lanzhou, Chinese Academy of Sciences

2. 合作者 近代物理所 黄明辉 甘再国 张志远 郁林 兰州大学核科学与技术学院 张鸿飞

3. 导言 • 当前世界上所有人工合成的超重核都是通过熔合蒸发反应机制，但是反应机制还不清楚。研究超重核合成机制对进一步合成超重核、确定超重岛的存在及其位置非常重要。 • 复合核的衰变与它的形成无关，所以它不能提供任何有关反应机制的信息。准裂变发生在复合核形成以前的反应中期阶段，与反应原子核的结构、形变、核核相互作用密切相关，携带反应机制的丰富重要的信息。 • 近十年来Adamian等一直采用Kramers公式来计算熔合反应中的准裂变。但Kramers公式是Fokke－planck方程在准稳态近似下的近似解，对实验值的描述不很好，它的适用程度有待推敲。 • 将双核之间的距离作为势场中的动力学扩散自由度来描述准裂变，出发点更基本。 • 在双核模型基础上，准裂变实验现象得到很好的描述，特别反应了壳效应和形变效应的影响。这进一步验证了重离子反应中双核模型的动力学行为。

4. T capture P CF fusion • CN • EN evaporation Dynamical description of the formation of SHN Schematic picture of the formation of SHN Dinuclear system (used to describe deep inelastic collisions of heavy systems): V.V. Volkov, Phys. Rep. 44(1978)93 Evaporation residue cross section:

5. QF yield treated by KRA-F W F. Li et al, Europhys. Lett., 64 (6), pp. 750–756 (2003) W.F.Li et al, J. Phys. G: Nucl. Part. Phys. 32 (2006) 1143–1155

6. 系统势能面（驱动势） 结构效应、壳效应包含在结合能中，核核相互作用用折叠势计算 Q.F.Li et al Eur. Phys. J. A 24, 223{229 (2005)，库仑相互作用用C.Y.Wang的解析公式计算

7. The master equation The fusion and QF are treated consistently as a diffusion processes in one master equation. Fusion probability and cross section: M.H.Huang et al, Phys.Rev. C 82, 044614 (2010)

9. Potential energy of the DNS The PES for the reaction 48Ca + 244Pu as a function of mass asymmetry and relative distance variable.

10. Mass yields of the reaction 48Ca + 244Pu calculated with DIFF and KRA-F, respectively. (a) Mass range from A1= 50 to A1= ACN/2. (b) Mass range from B-G Point (A1= 19) to incident Channel (A1= 48).

11. －0.51

12. (a) The driving potential of the reaction 48Ca + 244Pu as a function of the fragment A1. The open circles stand for the driving potential, in which the potential value at A1 = 113 is artificially substituted by that of A1= 112. (b) The mass yields shown by black squares and stars as a function of the fragment A1 under the driving potential given by black squares in (a) (except at A1 = 113, at all other places, the open circles are located on the black squares), calculated by DIFF and KRA-F, respectively. Open circles are the yields’ distribution under the driving potential by open circles.

13. 动力学形变的影响

14. The master equations Huang et al, PRC84,064619(2011)

16. The potential energy surface(the driving potential) Q.F.Li et al Eur. Phys. J. A 24, 223{229 (2005)

17. PES for the reaction 48Ca + 244Pu as a function of quadrupole deformations in the entrance channel(A1= 48).

18. The PES with the maximum distribution probability for different evolution times for the reaction 48Ca + 244Pu. GS, 0.5, 2, 8, and 20 indicate the interaction times t = 0,0.5, 2, 8, and 20 × 10−22 s, respectively.

19. (a, c) PES and QF yields for 48Ca + 244Pu at E∗ = 33 MeV along the mass asymmetry degrees of freedom using the DGS obtained from M¨oller’s table. (b) the PES with the deformation at a large interaction time; (d) QF yield with the method of DET. In (c) and (d), experimental data are denoted by circles. Pb

20. 48Ca+244Pu

21. Mass yields of the reactions 48Ca + 248Cm (a) and 48Ca + 238U (b) at E∗ = 33 MeV compared with the experimentaldata.

22. Summary • 建立了质量不对称度和双核之间距离的2变量的主方程，自洽地用主方程同时描述核子转移形成复合核和两核间距离的变化产生准裂变的过程。在更基本的基础上研究了重离子反应中的准裂变质量分布，表征了双核模型动力学行为的灵敏特征，检验了多年来使用Kramers公式的适用性。 • 准裂变产额分布显示了很强的结构效应。 • 把质量不对称度及两个核的轴对称四极形变作为动力学变量建立了3变量的主方程。原子核内禀性质与动力学形变的耦合通过系统驱动势中的原子核质量，驱动势因此与时间有关。 • 显示了详细的反应细节：准裂变质量分布与驱动势及其中的壳效应、动力学形变密切相关。 • 在双核模型基础上，准裂变实验现象得到很好的描述，特别反应了壳效应和形变效应的影响。这进一步验证了重离子反应中双核模型的动力学行为的合理性。

23. Thank you

24. The time evolution of the mass yields of the reaction 48Ca + 244Pu calculated with DIFF with t0= 10−22 s.