The main object of this study is the simulation, using the MCNP5 code, of the irradiator 226Ra-Be unit which is available at the physics department of the sciences faculty, Damascus University to calculate the neutron fluxes. The simulation results showed that neutron fluxes, in the energy ranges: thermal (10.9 MeV to 10.6 MeV), fast (0.11 MeV to 12.0 MeV), and medium (10.5 MeV to 10.1 MeV). Where flux percent was about (thermal 70.0%, fast 18.0% and medium 12.0%). The calculation of activity for a silver foil, in a specific time after irradiation, was simulated and compared with the experimental results. The comparison shows good agreement between the simulated and measured activity.