Abstract: Some large diameter ducts through the shielding wall of the electronic irradiation equipment such as the radiation cable channel, will inevitably reduce the shielding capacity of the shielding wall. In this research, target photon spectrum of 3 MeV electron irradiation accelerator was divided into two segments: below and above 1 MeV. Distribution of radiation fields near the ducts' outlet were simulated at different inclination angles of pipes using the Monte Carlo code MCNP. As angle design is closely linked to shielding wall thickness, influence on the radiation field from two ranges of energy levels with different wall thickness were also compared. The results showed that scattered radiation field at the duct outlet was almost unchanged when photons of different energies passed through the shielding wall with the angles of the pipe no less than 45°. The fields of penetrating radiation outside the wall could be ignored for photons below 1 MeV. With the increase of inclination angles, the influence was significant for photons above 1 MeV. In addition, with the increase of wall thickness, lower energy photons were attenuated rapidly and the contribution from higher energy photons took the dominant role.

Key words: electron irradiation accelerator, inclined angle, duct, MCNP