In this work, we conducted experimental and theoretical investigations on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique in two different single mode optical fibers, designed to be radiation resistant, with the aim to understand their behavior under irradiation and their radiation hardness as a function of core/cladding dopants. The first fiber is sold by the manufacturer to be used in harsh environments and has doped core and pure-silica cladding, while the second one is radiation-hardened with pure-silica core and F-doped silica cladding. Gamma irradiation was performed at a 60Co source with a 0.2 kGy/h dose rate, until a total absorbed dose close to 30 kGy was reached. During the experiments, the LPGs spectral changes were recorded in real-time, moreover pre- and post- irradiation investigations were done to establish the impact of gamma radiation …