| Positron or electron-atom collision theory is a main and fundamental area of atomic and molecular physics. The theory of atomic collisions is fundamental to many branches of physics and astrophysics. Many application fields need strongly for the cross section of positron or electron-atom scattering.In the past ten years positron-atom scattering has become a very interesting topic in both experimental and theoretical atomic collision studies. As an alternative to electron-atom scattering, both the similarities and the differences between electrons and positrons mean that positron scattering provides a useful, and sometimes more sensitive, test of the techniques used to study the electron-scattering processes.Although positrons differ from electrons only by the sign of their electric charge, the scattering of positrons by atoms is very different from the corresponding electron-atom scattering. This change in charge sign not only affects the dynamics of the collision, (for example, there is no exchange and the static interaction is repulsive for positron impact) but also the partitioning of the overall scattering (positronium formation and annihilation channels are open only for positron impact). There have been a number of theoretical studies for the positron atom systems, such as R-matrix Method, Close-Coupling Method, Borm approximation and so on. Most of the methods have limitations. For example, the variation calculations were restricted to a few partial waves in the low energy below the positronium threshold. The perturbative methods for positron-atom scattering omitted Ps formation and ionization channels. The Born approximation only works well in the high energy region of incident energies and the Close Coupling Method is satisfied to the low energy region of incident energies. In 1990, Hewitt attemped the first realistic coupled-channels calculation with explicit coupling to the Ps channels in the intermediate energy region. The theoretical methods in electron scattering by atoms can not completely overshadow positron scattering theory. Theoretical and experimental works in the positron scattering field still have more work to do. Recently, experimental measurements (in particular, by the Wayne State University group) have spurred a great amount of theoretical activity on studies of ionization, charge transfer and total scattering cross sections.The alkali-metal atom is an interesting target, which have unpaired electrons in the s subshell. Because of the existence of the unique valence electron 'staying' alone in the outer most shell far away from the core electrons, the target can treat as a hydrogenlike atom. Some traditional (and reasonable) approximations could then be considered for the calculation of the scattering. At the intermediate energy region, all the channels including the continuum are opened in the positron-atom system. The ionization also is a very significant channel in the positron scattering from atom. It is difficult to deal with the continuum states. On the theoretical side, a number of calculations of cross sections, elastic as well as total, for positron-alkali-metal atom systems at intermediate energies have been carried out. For the scattering of intermediate energy positron by atomic rubidium, various cross sections have been calculated by T.T. Gien, McEachran et al and Kermoghan etal. In the present thesis, we use the Coulped-Channels Optical potential method (CCO) to calculate the differential, integrated, ionization and total cross section for positron scattering from the alkali-metal atom rubidium at intermediate impact energies. The CCO theories is described in terms of the Fesh-bach projection operator formalism. The complete set of target states is divided into two complementary subspaces by means of projection operators P and Q. P space consists of a finite set of discrete channels, including the entrance channel in which the target is in its ground state. The remaining channels, including the continuum, comprise Q space. The CCO meth...
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