Shielding simulations for safe use of curtain electron accelerator by MCNP4C

In an electron curtain accelerator, when the electron beam passes through the titanium exit window of the accelerator chamber, X-ray photons are produced as a negative by-product of retarding accelerated electrons. Controlling the produced X-ray photons to avoid their detrimental effects or in fact, proper shielding of the accelerator is an important issue that has to be considered in the use of electron accelerators. In this work, based on the proposed geometry for a certain electron curtain accelerator, and using the MCNP4C code, the bremsstrahlung X-ray dose due to the collision of an electron beam with constant current of 50 mA and various energies within 100 ~ 300 keV energy range with the 13 µm-thick titanium foil were simulated. The results indicate a reduction in the bremsstrahlung X-ray dose from 685 Gy to 176 Gy per unit time for an increase in the electron beam energy from 100 keV to 300 keV. Moreover, the simulated values of the simulated radiation stopping power by the MCNP4C for the mentioned increase in beam energy, showed an increasing trend from 0.012 MeV.cm2/g to 0.021 MeV.cm2/g .The maximum and minimum percent deviation of the simulation and theoretical radiation stopping power were 33% and 3%, respectively. The energy loss due to Bremsstrahlung X-rays for an electron passing through a 13-μm thick titanium foil in the energy range of 100 ~ 300 keV, was calculated to be 7.19×10-2 up to 12.44×10-2 keV.  In addition, based on the simulated results obtained for the accelerator shield using the MCNP4C code, the optimum thickness of the lead shield for the maximum electron energy of 300 keV, was found to be 2.5 cm.