Accurate detection and localization of radioactive materials is crucial in nuclear imaging, especially given the growing threat of attacks and proliferation of nuclear power plants. A dependable imaging system capable of detecting gamma rays at varying distances is essential for timely identification and localization of radiation sources. Coded aperture imaging (CAI) is a promising method due to its ability to capture more photons and produce higher quality images, albeit more complex. The resolution of decoded images can be improved with the maximum likelihood expectation maximization (MLEM) algorithm. In this study, the GATE code was used to simulate a gamma camera with mosaic MURA coded apertures, with a NaI(Tl) detector measuring 27 × 27 × 2 cm³, to image sources of cesium-137 and americium-241. An angular resolution of about 7 degrees was achieved at a distance of 3 meters. estimated minimum equivalent dose for imaging at a distance of 10 meters using the cesium-137 source was 0.179 nSv/hr (with an activity of 6 microcuries). The signal-to-noise ratio at this distance was equal to 3.10, but after applying the MLEM algorithm, it increased to 17.96. The importance of this research lies in its potential applications for nuclear disarmament, border monitoring, and decontamination, where the location of radioactive sources is often unknown.