<p>A 4&#xa0;MeV RF linear accelerator for electron beam irradiation applications has been developed at the PBP-CMU Electron Linac Laboratory, Thailand. The system has been reengineered using a decommissioned medical linear accelerator. The main components include a thermionic DC electron gun, an RF linear accelerator, a beam diagnostic chamber, and a beam exit window for electron beam irradiation. Therefore, reengineering must be performed based on the characteristics of the electron beam and its dynamics throughout the system. In this study, the electron beam current density emitted from the cathode was calculated based on the thermionic emission theory, and the result was used to produce the electron beam distribution in the gun using CST Studio Suite^® software. The properties of the electron beam and its acceleration in the linear accelerator and downstream diagnostic section were studied using the ASTRA electron beam dynamics simulation code, with the aim of producing an electron beam with an average energy of 4&#xa0;MeV at the linear accelerator exit. The transverse beam profile and electron deposition dose in the ambient environment were calculated using Geant4 Monte Carlo simulation software to estimate the beam performance for the irradiation experiments. The parameters studied can be used as guidelines for machine operation and future experimental plans.</p>