One of the methods for investigating defects in metallic and non-metallic solids is to measure positron life time in these materials (positron life time spectroscopy). In this work by using a positron emitting source 22 Na which emits a 1.274 MeV gamma ray almost simultaneously with positron, defects in the metal samples aluminum and copper and also polymer samples polyethylene, poly tetra flour ethylene and poly methyl metha crylate have been studied. For this purpose a fast/slow advanced coincidence system consisting of two BaF 2 detectors, two timing single channel analyzers, two constant fraction discriminators, two amplifiers, two fast preamplifiers, a time to amplitude converter and a fast coincidence device, were used. Initially each device in the coincidence system was adjusted with the help of an advanced oscilloscope, and then the time resolution of the coincidence system was determined using a 60 Co source (which emits two simultaneous gamma rays of energies 1.33 and 1.17 MeV). The time resolution was found to be 156.74 ps. After adjusting the coincidence system, the 22 Na source was placed between the samples under study, and then the source and the samples were placed between the two barium fluoride scintillators. The 1.274 MeV gamma ray which is emitted from the source, almost simultaneously with the positron was considered as the start ray and the 0.511 MeV gamma ray which is created from positron annihilation with the electrons in the bulk or defect in the sample, was considered as the stop ray and these gamma rays were guided into the two barium fluoride scintillators. Positron life time spectra were measured in the samples under study using the time difference between 1.274 and 0.511MeV gamma rays. The spectra obtained were then analysed using the LT9-2 software. The metal samples were analysed by methods of Auto and Ser and the polymer samples were analysed by the four component method, and the positron and positronium life time components and their intensities were determined. The life time components in metal samples (Al and Cu) were then used to determine the vacancies in these samples. Also the life time components of ortho-positronium in the polymer samples were used to determine the size of cavities in these samples with an accurate of almost 0.1 nm. Keyword : Positron Life time Spectroscopy, positronium, 22 Na Source, positron life time in material, coincidence system, time resolution, vacancy, defect in samples, tao-eldraop.