Gamma treatment:
Gamma rays are electromagnetic waves, comparable to light,
infrared or UV, but with much smaller wavelength and therefore higher
energy. They belong to the ionizing radiation, because their energy is
sufficient to interact with the electron shell of material and create
radicals inducing chemical reactions.
These reactions are used primarily for radiation sterilization. The
radiation source for industrial sterilization applications is
exclusively cobalt 60.
| Studer
IR-168 Gamma Irradiator |
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Gamma rays have the following properties:
- Very reliable operation, as
continuous precise and reproducible treatment is practically
"built-in".
- Good penetration capabilities: for a one- sided treatment
after 12 cm
at density 1 still 50% of the initial dose is present. By treating the
goods from several sides, penetration and homogeneity can be further
improved.
- Slow accumulation: for a sterilizing dose of minimal 25 kGy
typically
an exposition time of several hours is required.
Cobalt 60
Cobalt 60 is an isotope of cobalt being produced from "normal" cobalt
59 by neutron flux in a nuclear power reactor. The exposition time for
activation is normally 18 to 24 months. The cobalt 60 atom is unstable
because of the extra neutron. It will spontaneously decay into nickel
60 with a half- life of the reaction of 5.26 years. 2 Gamma quants are
emitted for each decay, with energies of 1.17 and 1.33MeV. As the
cobalt 60 is double- encapsulated in stainless steel cylinders, it is
used as a closed energy source. Cobalt 60 can never get into direct
contact with the goods to be treated. The energy sources are in use for
20 years and will be sent back to the supplier for recycling or
disposal. Finally, after latest 150 years, the activity of the source
will be back to the normal level of the environment, so no long-term
disposal problems will occur.
| absorption
properties of Gamma radiation for one-sided treatment |
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| resulting
situation for a double-sided treatment |
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| Product
Carrier |
Co-60
Source Rack |
Control
Room |