The global shortage of Helium-3 supplies has spurred the search for alternatives to fast neutron detectors. This study proposes a detector that uses helium-4 (He-4), an abundant and stable isotope, as an alternative material. Using Monte Carlo simulations with the Particle and Heavy Ion Transport Code System (PHITS) software, researchers evaluated the fast neutron detection performance of the He-4 detector. The simulation results show that fast neutrons interact with He-4 nuclei mainly through elastic scattering (n, α), which produces alpha particles (recoil nuclei) that cause ionization and emit light signals. Research shows that the He-4 detector is highly sensitive to fast neutrons and less sensitive to gamma rays. Moreover, the detection efficiency of the detector increases when the pressure of the He-4 gas inside is increased. These results demonstrate the feasibility of using He-4 as an effective material for the fabrication of fast neutron detectors. This is a potential, low-cost, and safe solution.