Both beta and gamma rays are suitable for sterilization. The main difference between them lies in their depths of material penetration and their dose rates:
- Beta rays: high dose rate and limited penetration depth
- Gamma rays: high penetration capability and relatively low dose rate
The energy-rich beta or gamma rays destroy the DNA of the microorganisms, thus inactivating them. Radiation sterilization is thus the only process that enables products, including their packaging, to be sterilized without any appreciable increase in temperature – and without the use of chemicals, which always involves the problem of residues. Even the contaminated inner surfaces of closed packages, or components with complex geometrical shapes, are safely and reliably sterilized by high-energy radiation. These benefits make radiation sterilization a simple, effective and environmentally friendly alternative to other methods.
Beta rays are characterized by their ability to irradiate individual packages within a few seconds. In this way, under optimum conditions a complete truckload can be sterilized within a few hours. Your advantage: products can be processed promptly, avoiding warehousing and the associated tie-up of capital. The limited penetration depth of the electrons makes it necessary to unpack and re-pack the goods from the transport pallets. At our location in Saal, a fully automatic plant handles large quantities of goods within a short time.
Beta rays or accelerated electrons are generated by electron accelerators, which can be compared to a cathode ray tube. A hot cathode emits electrons which are accelerated in a strong electrical field and a high vacuum. If energies greater than 5 MeV are required, BGS uses resonance accelerators of the Rhodotron® type. In these, electrons are accelerated in a cyclic alternating field in several stages to a maximum energy of 10 MeV.
On leaving the accelerator, the electron beam is deflected in a magnetic field, so that it reaches the products to be irradiated as a fan-shaped beam. The products are conveyed through the irradiation field by an appropriate handling system.
The process characteristics of beta radiation differ fundamentally from irradiation using gamma rays. The products generally pass through the irradiation process in their final packaging as individual cartons, as loose bulk goods, or as ‘endless’ (continuous) products unwound and re-wound from reels. The irradiation process only lasts a few seconds. The height to which goods can be stacked for irradiation depends on their density, the packing scheme and the energy of the electrons.
Unlike the electron accelerators, in which the irradiation process is completed in a few seconds, irradiation in the gamma plant takes several hours. The gamma rays result from the decay of the radioactive isotope Cobalt-60 (60Co). They have a high penetration depth and can penetrate complete pallets or lots. The products to be irradiated can generally be conveyed directly through the irradiation process on the pallets they were delivered on, without repacking (industrial pallets: 1.20 x 1.00 m, euro-pallets: 1.20 x 0.80 m, heights up to 1.90 m).
A conveyor system transports the pallets into the plant, where they are then conveyed around the source rack which houses the radiation sources. The controls ensure that each pallet completes the number of cycles specified for it. In this way, the total gamma irradiation dose that has been fixed for each product is exactly adhered to. At the BGS gamma plant, different products requiring different doses can be irradiated at the same time. In order that the irradiation plant can be entered without danger, the source rack is lowered into a water basin, the water column shielding completely the radiation.