Abstract:
In this work, models were developed for calculating the S parameter (amount of positron
annihilation with valence electrons in low momentum regions) and W parameter (amount of
positron annihilation with core electrons in high momentum regions) of materials. Experimental
results obtained from Slow Positron Beam Research work for Aluminium and Silicon obtained
from the Department of Physics, University of Cape Town, South Africa, were used to test the
models. The models will be useful in the study of defects in materials. Moreover, the results of
this work will be useful in predicting the S and W parameters, and hence defect structural
characterization of materials, in studying the behaviour' of positrons in materials, and also to
study how defects in materials vary with any of the dependent parameters of the materials. The
models were developed based on parameters such as energy of incident beam, thickness of the
sample, illumination time that the S and W parameters depend on. The developed models contain
some mathematical functions which were in very good agreement with experimental values. The
correlation between the developed models and experimental values was calculated statistically
using the Spearman's correlation. High correlation between 0.72 and 0.99 was obtained between
the modeled and experimental values. The models obtained will be used as substitutes to actual
experimental work in making accurate predictions of the vertical defect profile of any material.
