Positron Impact Excitation Of 21s State Of Helium Atom Using A Distorted Wave Method

ABSTRACT

The study of excitation of helium atom by positron impact has drawn considerable

attention since the prediction of existence of the positron by Dirac in 1928.This is due to

the fact that the study of atomic collisions forms the basis for understanding of many

scientific phenomena in the planetary atmosphere and Astrophysical science. In this study

the excitation of helium atom to the is state by positron impact using the Distorted

Wave formula has been done. Previously, studies have been done on the above subject

both theoretically and experimentally but the results obtained disagree among

themselves. It is on this ground that this research was based. The interaction between the

charged projectile and target causes distortion to the projectile's wave functions in the

field of target and thus the Distorted Wave Method has been used to calculate the cross

sections. A computer program DWBA 1 originally written by Madison and Bartschat was

modified to perform the numerical calculations for positron-helium scattering and the

results obtained for both differential and total cross sections compared with the existing

theoretical and experimental data. This was done at incident energies between 30eY to

390eY. The agreement between the present integral cross section results and the

experimental results of Sueoka and the differential cross section results obtained using

present method and other methods especially at IOOeY, 200eY and 300eY was

satisfactory. Simple analytic wave functions for both the initial and final states of helium

atom were used. In the distorted wave method the initial state static potential of helium

atom was used as the initial state distortion potential and a linear combination of initial

state static potential and the final state static potential was used as the final state distortion potential.