Page 205 - Radiochemistry and nuclear chemistry

Radiation Effects on Matter 189

7.11.4. Industrial Radiation Processing
Today more than 140 6~ and 600 electron beam accelerator (EBA) irradiation
facilities are in use and in the following some of the more important uses will be
summarized.
Sterilization: There has been a steadily increasing demand for single use disposable
medical supplies (e.g. injection syringes, injection neeMles, surgical gloves) as well as surgi-
cal implants, contact lens solution and laboratory animal feed. Radiation sterilization doses
in the range 25 - 50 kGy have been adapted in many countries. Both 60Co and high energy
electron accelerators are used as radiation sources. Radiation sterilization has the advantage
of avoiding the use of toxic chemicals (e.g. ethylene oxide) and high temperature. A further
advantage is that the material can be sterilized after final packaging in a continuous process.
Wire and cable: Thermoplastics and elastomers are widely used as electrical insulating
material due to their physical properties and processability. Cross linking is an effective
means for improving e.g. the thermal resistance and tensile strength. EBA-irradiation ( ~ 50
kGy) affords a rapid, well controlled cross linking and is used by several major producers
of thin wires and cables.
Shrinkable film and tubing: Cross linked semicrystalline thermoplastics display rubberlike
properties at temperatures above their melting points. On deformation followed by fast
cooling the polymer maintains its deformed shape. The polymer returns to its original shape
when reheated. This memory effect is applied in the production of heat shrinkable films and
tubing. Radiation doses of the order of 40 - 100 kGy are used in the production of heat
shrinkable products.
Curing of surface coatings and inks: Irradiation is used onto cure printing inks and
varnishes and to bond coatings to surfaces of paper, fabrics, polymer films and steel. The
absorbed doses are in the range 10 - 100 kGy and use of accelerators with low energy and
high beam current affords selective energy deposition in the surface layer and high product
throughput. Industrial radiation curing lines are operating in car, wood panel and steel
industries. Due to the low electron energy, no heavy shielding is required and the
accelerators can easily be placed in normal industrial environment.
Potential applications: Immobilization or trapping of bioactive material such as enzymes,
antigens, antibodies and drugs in polymer matrixes by radiation processes have received
much attention.
Radiation treatment: To remove organics and metallic pollutants from waste water and
SO x and NO x from flue gases emitted from coal power stations and industrial plants have
been studied in great detail. The cleaning of flue gases has been developed to the pilot plant
stage.

7.12. Technical uses of small dose-rates

The ability of nuclear radiation to ionize gases is used in several applications. Static
electricity can be eliminated through the installation of an ~- or B-source in micro-balances.
Similarly, but on a much larger scale, elimination of static electricity is used in the paper,
textile and paint industries.