TY  - UNPB
N1  - Thesis digitised by ProQuest.
TI  - Studies of positron scattering near excitation thresholds
EP  - 50
Y1  - 2004///
AV  - public
M1  - Masters
KW  - Pure sciences; Positrons
A1  - Read, Alexis John
ID  - discovery10098024
N2  - Theoretical investigations have been made of positron scattering by a model one-electron atom whose lowest excitation threshold energy lies below the threshold for positronium formation. The principle purpose of this work has been to find out if there is any enhancement in the positron-electron annihilation rate near to the excitation threshold, as is known to exist near to the positronium formation threshold. A model one-electron atom with the required properties was constructed, and this target system was then incorporated into the positron-atom scattering formalism. The Kohn variational method was then used to calculate the elastic scattering phase shift and the associated total wave function at various energies in the range from zero up to the lowest excitation threshold of the model atom. The energy dependence of the positron-electron annihilation rate was then determined from the total wave function at the positron-electron coalescent point. A significant enhancement of he annihilation rate was observed close to the excitation threshold, suggesting that there may well be similar enhancement at other inelastic thresholds and resonances below the positronium formation threshold. The elastic scattering wave function has also been used to determine the angular correlation of the annihilation radiation, which provides information about the momentum distribution of the positron-electron pair at the moment of annihilation.
UR  - https://discovery.ucl.ac.uk/id/eprint/10098024/
PB  - UCL (University College London)
ER  -