Convergent close-coupling approach to positron-helium collisions
This thesis presents the theoretical studies of positron scattering on the helium atom using two-center Convergent Close-Coupling (CCC) theory.The thesis organized in the following way: In the Introduction (Chapter I) the motivation for the study and the current status of the positron-helium scatter...
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| Format: | Thesis |
| Language: | English |
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Curtin University
2010
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| Online Access: | http://hdl.handle.net/20.500.11937/1603 |
| _version_ | 1848743713871757312 |
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| author | Utamuratov, Ravshanbek |
| author_facet | Utamuratov, Ravshanbek |
| author_sort | Utamuratov, Ravshanbek |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | This thesis presents the theoretical studies of positron scattering on the helium atom using two-center Convergent Close-Coupling (CCC) theory.The thesis organized in the following way: In the Introduction (Chapter I) the motivation for the study and the current status of the positron-helium scattering problem are presented. Other theoretical methods that previously have been applied to this problem are reviewed and their limitations are indicated. The application of the two-centre CCC to positron-helium is presented in Chapter 2. The derivations of the scattering equations and transition matrix elements are given in detail. The results of the two-centre CCC calculations for positron scattering from the helium ground state are compared with available experimental data and the results of other calculations in Chapter 3. Chapter 4 presents CCC results of positron scattering from the metastable 2[superscript]3S excited state of helium. Finally, in Chapter 5, we draw conclusions arising from this work and indicate future directions for the research.Main results of this work • The two-centre Convergent Close-Coupling method is generalized to positron scattering on the helium atom. • Cross sections, free from pseudo-resonances, are obtained for all major channels of interest and over a wide range of scattering energy. The importance of the inclusion of pseudo-states from both centers is demonstrated. • The elastic cross section below the Ps-formation threshold is obtained, for the first time, by using a two-centre close-coupling approach. • A consistent agreement of the CCC calculations with the available integrated cross section measurements of Ps-formation has been achieved at energies from the threshold of 17.8 eV up to 150 eV.• The CCC calculations exhibit a qualitative agreement with the measurements of the total cross section for ionization of the ground state of helium by positron impact. • The separation of the spin part of the total wave function is demonstrated and possible ortho- to para- Ps formation ratios are derived from first principles without assumptions. • Calculations of positron scattering from the 2[superscript]3S metastable state of helium are done for the first time. Converged results for the total scattering, Psformation, helium and Ps excitation as well as breakup cross sections are obtained. • Both considered cases (scattering from the ground and the 2[superscript]3S metastable states) confirm the equal atomic and Ps contributions to near-threshold breakup cross section, a behavior previously observed in positron scattering from hydrogen. |
| first_indexed | 2025-11-14T05:49:57Z |
| format | Thesis |
| id | curtin-20.500.11937-1603 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T05:49:57Z |
| publishDate | 2010 |
| publisher | Curtin University |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-16032017-02-20T06:37:18Z Convergent close-coupling approach to positron-helium collisions Utamuratov, Ravshanbek helium atom positron scattering theoretical studies two-center covergent close-coupling (CCC) theory This thesis presents the theoretical studies of positron scattering on the helium atom using two-center Convergent Close-Coupling (CCC) theory.The thesis organized in the following way: In the Introduction (Chapter I) the motivation for the study and the current status of the positron-helium scattering problem are presented. Other theoretical methods that previously have been applied to this problem are reviewed and their limitations are indicated. The application of the two-centre CCC to positron-helium is presented in Chapter 2. The derivations of the scattering equations and transition matrix elements are given in detail. The results of the two-centre CCC calculations for positron scattering from the helium ground state are compared with available experimental data and the results of other calculations in Chapter 3. Chapter 4 presents CCC results of positron scattering from the metastable 2[superscript]3S excited state of helium. Finally, in Chapter 5, we draw conclusions arising from this work and indicate future directions for the research.Main results of this work • The two-centre Convergent Close-Coupling method is generalized to positron scattering on the helium atom. • Cross sections, free from pseudo-resonances, are obtained for all major channels of interest and over a wide range of scattering energy. The importance of the inclusion of pseudo-states from both centers is demonstrated. • The elastic cross section below the Ps-formation threshold is obtained, for the first time, by using a two-centre close-coupling approach. • A consistent agreement of the CCC calculations with the available integrated cross section measurements of Ps-formation has been achieved at energies from the threshold of 17.8 eV up to 150 eV.• The CCC calculations exhibit a qualitative agreement with the measurements of the total cross section for ionization of the ground state of helium by positron impact. • The separation of the spin part of the total wave function is demonstrated and possible ortho- to para- Ps formation ratios are derived from first principles without assumptions. • Calculations of positron scattering from the 2[superscript]3S metastable state of helium are done for the first time. Converged results for the total scattering, Psformation, helium and Ps excitation as well as breakup cross sections are obtained. • Both considered cases (scattering from the ground and the 2[superscript]3S metastable states) confirm the equal atomic and Ps contributions to near-threshold breakup cross section, a behavior previously observed in positron scattering from hydrogen. 2010 Thesis http://hdl.handle.net/20.500.11937/1603 en Curtin University fulltext |
| spellingShingle | helium atom positron scattering theoretical studies two-center covergent close-coupling (CCC) theory Utamuratov, Ravshanbek Convergent close-coupling approach to positron-helium collisions |
| title | Convergent close-coupling approach to positron-helium collisions |
| title_full | Convergent close-coupling approach to positron-helium collisions |
| title_fullStr | Convergent close-coupling approach to positron-helium collisions |
| title_full_unstemmed | Convergent close-coupling approach to positron-helium collisions |
| title_short | Convergent close-coupling approach to positron-helium collisions |
| title_sort | convergent close-coupling approach to positron-helium collisions |
| topic | helium atom positron scattering theoretical studies two-center covergent close-coupling (CCC) theory |
| url | http://hdl.handle.net/20.500.11937/1603 |