calculation and simulation of the designed shield for gamma industrial irradiator in bonab

calculations and simulation of the designed shield for bonab industrial irradiation unit has been investigated in this work. this irradiator is panoramic wet source storage which is used to irradiation of medical equipment, some kinds of food & healthcare products, spices, … in order to sterilization and increasing of durability. irradiation is performed in irradiation room using emitted photons of 60co source. the internal dimensions of the room is 10.5 (m) *7.1 (m) *3.2 (m) (l*w*h) which is made of ordinary concrete walls and roof with thicknesses of 2.1 m to reduce dose rate less than 0.1 µsv/hr out of the shield. two separated mazes have been considered as entrance of the room for passage of personals and goods and prevent leakage & streaming of radiation through ducts into outside. the calculations were performed with monte carlo mcnp4c code and variance reduction methods to obtain the dose rate in various layers and beyond the shield. the obtained results showed the safety of existent scheme for getting started the operations of the irradiation unit.