arXiv 0809.42562008-09-26physics.atom-phphysics.comp-ph

重离子碰撞中超临界Dirac共振的计算

Calculation of supercritical Dirac resonances in heavy-ion collisions

Edward Ackad

备注：: Thesis, 25 figures, 135 pages

摘要：

这种共振在性质上与原子物理学中的其他共振相似。它的参数是它的能量和寿命。将映射傅里叶网格法（MFG）这一数值离散技术推广到狄拉克方程，并用于求解准分子超临界1 S $σ$态的共振参数，铀-铀碰撞中。只使用MFG方法的直接方法给出合理的估计共振参数。然后应用解析延拓方法，如坐标的复缩放（CS）或添加复吸收势（CAP）。它们允许更准确地确定超临界共振参数。（外推）增广解析延拓方法被用来调查的影响，高阶耦合，超越的ESTA近似。对于U $^{92+}$ -Cf $^{98+}$的近电荷对称体系，研究表明，S-D四极耦合是仅次于电子相互作用的主导相互作用.库仑势垒附近的碰撞，其中超临界共振态发生，也使用MFG计算。给出了质心能量为740 MeV的U $^{92+}$ -U $^{92+}$碰撞的零碰撞参数库仑轨道的计算结果。本文研究了近距离核粘附对正电子能谱的增强效应。给出了2、5、10 $\times10^{-21}$ s粘附时间的结果。核粘附提供了实验证明超临界共振态态存在的可能性。

英文摘要：

This resonance is similar in character to other resonances in atomic physics. It is parameterized by its energy and its lifetime. A numerical discretization technique, the mapped Fourier grid method (MFG) is extended to the Dirac equation and is used to solve for the resonance parameters of a quasimolecular supercritical 1S$σ$ state which arises, e.g., in a uranium-uranium collision. Direct methods using only the MFG method are shown to give reasonable estimates for the resonance parameters. Analytic continuation methods such as complex scaling (CS) of the coordinate or adding a complex absorbing potential (CAP) are then applied. They allow for more accurate determinations of the supercritical resonance parameters. The (extrapolated) augmented analytic continuation methods are used to investigate the effects of higher-order couplings, beyond the monopole approximation. For the nearly charge symmetric system of U$^{92+}$-Cf$^{98+}$, it is shown that the S-D quadrupole coupling is the next dominant interaction after the monopole interaction. Collisions near the Coulomb barrier, in which supercritical resonance states occur, are also calculated using the MFG. Results are presented for the collision of U$^{92+}$-U$^{92+}$ for a zero-impact-parameter Coulomb trajectory at a center-of-mass energy of 740MeV. The enhancement effects to the positron spectrum due to nuclear sticking at closest approach is examined. Results are given for sticking times of 2,5,10$\times10^{-21}$s. Nuclear sticking is shown to offer the possibility of demonstrating experimentally the existence of supercritical resonance states.

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摘要：

英文摘要：

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