【作者】 郭大龙；

【导师】 马新文；

【作者基本信息】 中国科学院研究生院（近代物理研究所） ， 粒子物理与原子核物理， 2014， 博士

【摘要】 碰撞引起的原子分子过程，例如激发、电离和电子转移等，在揭示动力学机制等基础研究方面及实验室和天体等离子体等应用方面都很重要。过去对离子-原子碰撞的研究集中于高能区，对中能区的研究还比较匮乏。本论文工作利用反应显微成像谱仪技术，对50-100keV能量范围H+离子与He原子碰撞发生的单电子俘获过程和转移电离过程进行了实验研究，获得了态选择俘获截面、揭示了电子-电子关联作用并鉴别出动力学机制。为了对高能电子进行成像，通过计算和模拟束流动力学，我们对高能电子磁谱仪所涉及的磁铁系统进行了优化设计。对单电子俘获过程的研究表明，基态俘获是主要过程，而激发态俘获以及转移激发过程的贡献相对很小。对基态和激发态俘获过程，炮弹小角度散射占主导地位，说明动量主要通过俘获的电子转移，而核-核相互作用对此过程的贡献较小。与基态和激发态俘获相比，转移激发更倾向于在小碰撞参数时发生，核-核相互作用在此过程中也更重要。通过比较实验角微分截面结果和基于独立电子模型的计算结果，揭示出电子-电子关联效应在基态与激发态俘获过程中的作用可以忽略，但在转移激发过程中却比较重要。对转移电离过程，实验结果表明炮弹与电子和靶核动量交换占主导地位，电子主要通过炮弹-电子间的两体碰撞出射，两步机制在转移电离过程中比较重要。与考虑束缚能的电子两体碰撞出射特征比较我们发现，转移电离倾向于通过先转移后电离进行，且电子-反冲靶核这一高阶作用可能有贡献。对这里研究的中性化炮弹出射，在前向出射电子能谱上我们没有观察到之前文献中报道的cusp电子的贡献，通过初步分析我们认为对处于基态的中性炮弹出射不存在cusp电子，二次碰撞引起的假符合导致了文献中报道的cusp峰的出现。实验中同时获得了转移电离过程的全微分截面，这为理论提供了最严格的检验。高能电子磁谱仪利用磁铁系统对离子-原子碰撞中的高能电子出射角进行成像。通过对电子磁谱仪所涉及的束流动力学的计算和模拟，我们得到了能够满足成像条件的各种可能磁铁参数组合，经过比较确定了满足最好分辨的磁铁系统。进一步从传输矩阵出发我们对磁铁系统做了优化并提出了将来电子磁谱仪的最优设计参数。更多还原

【Abstract】 Ionization and electron transfer occurring in ion-atom collisions havefundamental importance in the study of the dynamics and potential applications invarious fields, e.g. laboratory and astrophysical plasmas. Most of these studies wereperformed at high impact energies while the studies in the intermediate energy rangeare rare. In this work, single-electron capture and transfer ionization occurring incollisions of protons with He at energies ranging from50to100keV have beenexperimentally investigated by means of a reaction microscope. We obtained thestate-selective cross sections, revealed the importance of the electron-electroncorrelations and the dominate mechanisms in these processes. To map the high energyelectrons the magnetic system of the high-energy electron magnetic spectrometer wasoptimized.It was found that for single electron capture the ground state transfer is thedominant reaction channel, and excited states transfer has relatively smallcontributions to the cross sections. Transfer excitation process has a minorcontribution to the total cross sections. From the angular-differential cross sections forthe single transfer process, it was found that the momentum transfer mediated by theelectron is dominant because of the large contributions of small-angle scatterings,while the nucleus-nucleus interaction has a minor contribution. Compared to the singletransfer process, the transfer excitation process is more likely to take place at smallimpact parameters, which implies that the nucleus-nucleus interaction is moreimportant in this process. A comparison between the present experimental results and the theoretical calculations within the independent electron model reveals that theelectron-electron correlation effects, which are negligible in the single transfer process,manifest their importance in the transfer excitation process.For transfer ionization, the experimental results indicate that the momentumexchanges between the projectile and both the recoil ion and the electron dominate inthis process. The electron momentum distribution projected onto the scattering planedisplays some features characterized by binary encounter electron emission. Acomparison with the binary encounter model involving the binding energy effectreveals that the transfer ionization is more likely to happen in a sequential order oftransfer first and ionization second. Besides, the higher-order effect involving theinteraction between the electron and the residual recoil ion may also contribute to theelectron emission features. Another interesting observation in our data is the absenceof the cusp-shaped electrons centered at a speed equal to that of the incident projectilein the forward direction. This is contrary to the previous results. A preliminary analysisindicates that for neutralized outgoing projectile with the captured electrons in theground state the cusp does not exist and the contamination due to the double collisionscould cause the cusp-shaped electrons reported in the literature. In addition, the fullydifferential cross sections measured in the experiment provided the most rigorous testof the theories.The high-energy electron magnetic spectrometer enables one to map the emissionangle of the high-energy electrons. The beam optics of the electron spectrometer havebeen calculated and simulated in detail. We obtained the magnetic parameters fulfillingthe mapping condition and determined the magnetic system with the best resolution. Afurther investigation using the transfer matrix presented the optimum designparameters of the magnetic system.更多还原