Radiating the product from both sides may also be necessary to achieve the desire dose uniformity. Figure 3 shows an example of this type of dose distribution when a product has been irradiated from both sides with a 10 Mev beam. Typically two sided irradiation is used when cross-linking relative thick products that need a reasonably high degree of dose uniformity. It is fairly common to use two sided irradiation for boxed, bulk products that are processed in the medical sterilization business. For single sided irradiation the most uniform dose would be achieved when the product density thickness results in the dose at the beam exit side of the product is equal to the surface dose at the beam entry point.
Dose is proportional to current density and exposure time.
K factor is empirically derived by performing dose tests with the particular beam of interest. The K factor is a figure of merit for the performance of the electron system. The equation above predicts bulk or mass throughput which is defined as the dose one can expect through the entire bulk of a product being passed under the beam under the conditions stipulated in the equation. If one wishes to predict surface throughput, you simply have to substitute meters per minute for kilograms per minute in the above equation to do so. Figure 4 shows a plot of surface dose K factor or figure of merit for low penetration equipment.