重离子熔合反应中的动力学形变

李君清中科院近代物理所

兰州大学核科学与技术学院

合作者

中科院近代物理所黄明辉，甘再国，张志远，周小红

兰州大学核科学与技术学院张鸿飞

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INTRODUCTION

在重离子核反应过程中，由于两核之间很强的核力与库仑力相互作用，两核会发生形变。

这种形变会改变核核相互作用，影响进一步的反应过程，不可忽略，是与反应时间有关的，称为动力学形变。

这是很重要的物理量，形变牵扯到多核子位置的改变，内禀态则有较大的变化。由于集体自由度与内禀自由度的完全耦合对重离子反应迄今还不可能，因此动力学形变迄今没有得到很好的解决。

本工作将形变参数当作动力学随机变量，与核子转移相互关联，由三变量的主方程统一自洽描述。

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The master equations

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反应系统势能面（驱动势）

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(a): The interaction potential between colliding nuclei in the entrance channel along internuclear distance for the reaction 48Ca+244Pu. (b): The QF barrier related to quadrupole deformations in entrance channel.

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Part of the PES in positive deformation region of the reaction 48Ca+244Pu at 1= 48(a) and 1= 86(b). Point I is the incident channel. The values in parenthesis are the deformations of projectile-like(A,C) and target-like nuclei(B,D), respectively.

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The probability distribution as a function of the deformations of reaction 48Ca+244Pu

at different interaction times for 1 = 48.

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The probability distribution as a function of the deformations of reaction 48Ca+244Pu at different interaction times for 1= 86.

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The solid line denotes the probability rate (P(B)/P(A)) varying with interaction time of peaks B and A; the dot line denotes the rate (P(C)/P(D)) of peaks C and D.

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(a): Part of the PES in positive deformation region of the reaction 48Ca+244Pu at A1= 58. (b): the probability rate (P(E)/P(F)) varying with interaction time of peaks E and F in (a).

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The probability distribution as a function of the deformations of reaction 48Ca+244Pu at different interaction times for 1 = 58.

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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.

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Mean values of the deformations of fragments A1 and A2 at different reaction times for the reaction 48Ca +244Pu. GS, 0.5, 2, 8,and 20 indicate the times t = 0, 0.5, 2, 8, and 20 × 10−22 s, respectively.

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(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.

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

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(a) Comparison of the inner fusion barrier using DGS vs DET. One of the arrows indicates the entrance channel.(b) An enlargement of the upper part of (a). (c) Fusion probabilities related to the excitation energy at zero incident angular momentum using DGS vs DET.

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Comparison of the evaporation residue cross sections among the results using DGS (dotted lines), DET (solid lines), and available data of Dubna and of TASCA(GSI) for the reactions (a) 48Ca + 244Pu and (b) 48Ca + 248Cm.

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总结

• 在双核模型框架下，重离子熔合过程中的两个核的动力学形变及核子转移被处理为动力学扩散过程而自洽地处理，建立和求解了以两个核的四极形变参量和质量不对称度为变量的三变量主方程，从而改善了双核模型。

• 系统的势能面由此三变量确定，他们又通过主方程制约此三个变量的演化。形变是集体自由度，一些原子核的内禀性质如：壳效应、对效应，同位旋对称性、内禀激发性质等等与形变自由度的耦合虽然没有显处理，但他们通过驱动势中碎片质量而相互关联。在此基础上处理了导致超重核的熔合过程与准裂变的竞争，给出了一些反应机制的信息。

• 核子转移、两核形变变量在反应过程中相互关联。制控核子转移的势能面与形变有关，因此是与反应时间有关的。

• 对每个质量不对称度，得到了各不相同的形变的弛予时间。• 所计算的准裂变质量产额分布及产生超重核的蒸发剩余截面激发函数与实

验结果符合很好。• 本工作是对双核模型的有力支持。

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Thank you