Along with radiation sensing, necessity to study and design reliable radiation hardened devices is also increasing now-a-days. These devices are tolerant to high dosage of radiations without causing any physical damage, logic damage or data loss. In the current work, stacked gate Junctionless FinFET (SG JL FinFET) is analyzed as radiation hardened device by studying the impact of radiation of Linear Energy Transfer (LET) values ranging from 2MeV.cm/mg to 10MeV.cm/mg on the device performance. The proposed radiation hardened FinFET is experimentally calibrated with pre and post irradiation data. Single event upset (SEU) study using transient analysis is carried out to study the performance of proposed radiation hardened device at microwave frequency. High-k material-hafnium dioxide is used as gate oxide material to improve radiation hardness of SG JL FinFET. Electrical parameters-drain current, surface potential and SEU generation rate are studied to analyze device characteristics. Optimization of gate oxide, doping concentration, gate metals and temperature is carried out to enhance the reliability of device in terms of radiation hardness. SG JL FinFET is exposed to different types of waves-UV rays, X-ray, and Gamma rays to study the response of device at different frequencies. The comparison of SG JL and SG Inversion Mode (IM) FinFET has been performed. Comparison of SG JL FinFET with previously reported Inverted mode FinFET, L-shaped tunnel FET and Fully Depleted Silicon on Insulator (FD-SOI) MOSFET is carried out to find most suitable device which can provide highest immunity to radiation exposure. Response of JL FinFET based CMOS inverter in presence of radiation is studied and is also compared with other available CMOS inverters.