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12C+12C熔合反应天体物理S *因子的研究现状

The Current Status of Astrophysical S*-factor Studies for the 12C+12C Fusion Reaction

  • 摘要: 近二十年来,中子星表面由12C+12C熔合反应触发的超级X-射线暴天文观测结果,无法用现有的基于外推得到的12C+12C熔合反应率解释,因此对极低库仑势垒能量下12C+12C熔合反应截面进行测量成为了核天体物理研究的一个热点。然而,超级暴典型的12C+12C熔合反应伽莫夫窗口为1.5±0.3 MeV,远低于熔合反应库仑势垒。这使得用直接测量方法对该能区内极低的熔合反应截面进行研究成为一个巨大的挑战。特洛伊木马方法实验(THM)是目前唯一能给出伽莫夫窗口内各出射道激发函数的带电粒子测量实验,然而其结果目前仍存在很大争议。本工作回顾了12C+12C熔合反应直接测量实验的研究现状,并对THM的数据分析结果提出了新的解读。结合全同玻色子体系理论对THM提取的复合核24Mg激发态进行讨论,首次给出12C+12C熔合反应入射道无量纲约化宽度推荐平均值 \theta ^2 =0.031,与反对称分子动力学模型(AMD)在相应能区的理论预言相一致。

     

    Abstract: Over the past two decades, astronomical observations of superbursts, initiated by the 12C+12C fusion reaction on the surfaces of neutron stars, have remained elusive by theoretical models based on the reaction rate of 12C+12C fusion reaction. Consequently, direct measurements for the cross section of the 12C+12C fusion reaction at energies well below Coulomb barriers have become a hot topic in nuclear astrophysics. For typical superbursts, the Gamow window energy of the 12C+12C fusion reaction is 1.5±0.3 MeV, significantly lower than the Coulomb barrier. This makes it a huge challenge to directly measure the extremely low cross section of the fusion reaction in the corresponding energy region. The experiment by the Trojan Horse Method (THM) is the only charged-particle measurement providing the excitation functions for all exit channels within the Gamow window. However, the experimental results still remain highly controversial at present. This work reviews the current status of direct measurement experiments for the 12C+12C fusion reaction and provides a novel interpretation of the data for THM. Combining the theory of identical boson systems, the compound nuclear excited states in 24Mg extracted from THM are discussed. For the first time, a recommended average value of the dimensionless reduced width for the entrance channel of the 12C+12C fusion reaction is provided as \theta ^2 =0.031, which is consistent with theoretical predictions in the corresponding energy region from the antisymmetrized molecular dynamic (AMD). Furthermore, the reduced-width amplitude for the entrance channel of the 12C+12C fusion reaction within the Gamow window is suggested as \theta ^2 =0.031.

     

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