Continuous-type gamma irradiators

In conveyor bed systems the product is packed into tote boxes, termed irradiation containers. These are supported from beneath by rollers or trays along which the containers are transported into the irradiator, past the source, and back out again. Figure 2 shows the Nordion JS 8500 continuous-type gamma irradiator. In this sterilizer the irradialion container is an aluminum tote box approximately 900 mm high. 600 mm in length, and 400 mm in depth. The 400 mm dimension separates the two sides of the tote, which alternately face the incident radiation as the container is moved from one stretch of the conveyor to the next. 

Conveyors There must always be some mechanism within industrial gamma irradiators for moving product around the source and in and out of the cell. On the basis of the type of conveyor used, gamma irradiators may be designed for continuous or batch operation. 

Figure 28 Schematic presentation of the relative situation of the different types of radiations used in therapy. Two criteria are considered the physical selectivity and the LET (or radiobiological properties). For the low-LET radiations, the physical selectivity was improved from the historical 200-kV x-rays to cobalt-60 gamma rays and the modern linacs. Even with the linacs today, significant improvement is continuously achieved (IMRT, etc.). Among the low-LET radiation, the proton beams have the best physical characteristics, but one of the issues is the proportion of patients who will benefit from proton irradiation. A similar scale can be drawn for high-LET radiation the heavy-ion beams have a physical selectivity similar to protons. Selection between low- and high-LET radiation is a biological/medical problem it depends on the tumor characteristics, and reliable criteria still need to be established (see text). (From Ref 54.)...

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