Abstract: Due to its special design, there are some gaps between the fixed and rotating shielding components of a rotary blood irradiator. In the EIA process of programs of such kind, the leakage dose resulted from this defect is often paid more attention. The Monte Carlo method was employed to calculate the dose. It's confirmed that, in the case of a 2 mm wide slit, the contact dose rate meet requirements of pharmaceutical industry standards.

Key words: Blood irradiator, Leakage dose, Monte-Carlo method