Generation of positron lifetime spectra in defective metals.

The lifetime spectra are usually obtained by the convolution of the decay function with time response function. The aim of this work is to generate the lifetime spectra in defective metals. Different defects concentrations and more than one type of defects are considered. A computer program was designed to generate the decay
function for multi-component and time response function then convoluted them and superimposed with random coincidence (background). This program was named "GLTS". The factors affecting the lifetime spectrum (resolution, lifetime component, random coincidences, intensity, and shift ) are investigated and discussed. Also the generated spectra were tested and compared with experimental spectra of positron annihilated in metals that contain defects initiated due to a plastic deformation rocess. Moreover, the recovery of these defects at different annealing stages are considered in the generated spectra. The results proved that the GLTS program can be distinguish small values differences (of about 25ps) between lifetimes components. These small values of lifetime components with small values of corresponding intensities lead to difficult decomposition. The time resolution of worse than 800ps leads to difficult decomposition except for high values of lifetime (i.e. in ns). The results show that distortion in the experimental lifetime spectra increases when background-to-peak ratio increases above than 1%. Moreover, the distortion in the lifetime spectrum increases when the shift between the centroid of the Gaussian functions describing the response function increases above 40ps.