Method for irradiating in an irradiation chamber products being stored in the form of pallets or in the form of bulk material in appropriate containers by means of a high energy X-ray beam source including the following steps: placing and arranging the products onto two different levels of products, so that a first set of products is placed on an upper level and a second set of products is placed on a lower level; irradiating both sets of products during a first period of time; submitting the products arranged on the two levels to a switch or transposition, so that the set of products arranged on an upper level is arranged on the lower level and vice versa and irradiating during a second period of time the new arrangement formed of the two transposed sets of products.