质子碰撞电离过程中程函近似效应的理论研究

Influence of eikonal-initial-state on ionization of atom by proton

分别利用连续扭曲波方法和初态程函近似-连续扭曲波方法对质子碰撞电离氖原子1s,2s,2p壳层后随电离电子能量变化的单重微分散射截面(SDCS)和二重微分散射截面(DDCS)及总截面进行了计算,所得结果与部分实验数据符合得很好.详细探讨了各壳层SDCS和DDCS的细致结构以及质子碰撞的电离机制.结果表明,对于氖原子2p壳层,随着入射质子能量的增加,SDCS的区域变长,幅度减小,在低能区以软电离为主;而DDCS出现的峰均迅速减小.此外,分析了初态程函近似对SDCS和DDCS的影响,发现该效应对截面的影响在低能入射时非常明显,随着入射能量的增大,这种影响逐渐减弱.

Apart from its fundamental importance, ionization phenomenon of atoms by impact of energetic charged particles has practical applications in various kinds of plasmas, in radiation physics and in the study of penetration of charged particles through matter. Compared with other processes, this particular reaction helps to reveal many details about the dynamical process and the level population, and, in fact, can provide a new insight into and a promising route to studying the e-p interactions in the presence of Coulomb field. The development of ion sources producing multiply charged ions and of antiproton beams allow us to change the potentials and hence the whole final momentum distribution. A great variety of experimental conditions allowed by changing the projectile charge and velocity constitute a stringent test for theory. The continuum-distorted-wave eikonal-initial-state （CDW-EIS） approximation model has emerged as a reliable method to compute cross sections for different projectile/target combinations from intermediate to high non- relativistic impact energies. This model is of the first order in a distorted-wave series. It takes into account the long-range behaviour of the Coulomb potential and includes the distortion of the target states in both the initial and final channels. In the present work, the single different cross sections （SDCS）, double different cross sections （DDCS）, and total cross sections for single ionization of ls, 2s and 2p shell of Ne atom by impact of proton are calculated in the framework of continuum-distorted-wave （CDW） method and the CDW-EIS approximation model, respectively. The influence of the eikonal-initial-state on the cross section, and the mechanism of the proton-atom collision ionization are discussed in detail. Moreover, the structures of the SDCS and DDCS of each shell are studied and the ionization mechanism of soft collision, electron capture to the continuum state, binary encounter collision are demonstrated. Our results show that for the 2p shell of Neon, as the incident proton energy increases, the region of the SDCS becomes larger and the soft ionization turns dominant in the low energy region. The eikonal-initial-state effect on the cross section is obvious in the lower energy region, yet smaller as the incident energy increases. These effects on the DDCS are greater than on the SDCS. The present CDW-EIS and CDW results are compared with the experimental data available in the energy range of 1 5000 keV/u for H＋on Ne in the literature, showing that they are quantitatively in good agreement. In general, the CDW-EIS describes well the multiple ionization above 50 keV/u, showing a clear tendency to coalesce with the CDW at high energies.