Co-shielding is adopted in this study as preliminary investigation in order to assess the potential of a radioactive pigging system in leak detection application. Pipe inspection gauge (PIG) is the insertion of an encapsulated system inside the underground pipeline to detect the leakage along the pipe under investigation. The developed PIG comprises of radiation sensor, data logger, and battery to power up the system. The radioactive source is injected inside the fully occupied pipeline and seeps through any cracks and stays outside of the pipeline. The launched PIG picks up the radioactive signals that signifies the location of the leak. Normally, the encapsulated system is made of stainless steel or aluminum material. A 25.4-cm mild steel pipeline is set as pipe under investigation, and the distance between PIG and pipe is set as 150 cm. In this paper, a desktop experiment is undertaken and discussed in order to optimize the gamma intensity received by the radiation sensor, the thickness of the material, and the type of co-shielding materials, respectively. A desktop experiment is a simple radioactive set up to describe the gamma attenuation effect with different configurations. Sodium iodide (NaI) as scintillation detector is used as the radiation sensor and Cs-137 (energy of 0.662 MeV and half-life of 30 years) with activities of 74 MBq and 740 MBq as low and high activities are adopted in this study. Moreover, mild steel–aluminum (MS-Al) and mild steel–stainless steel (MS-SS) with different configurations are used as co-shielding material for gamma attenuation study.