Sep 9, 2009

Microwave: (Radiation Sterilization)

Introduction :

Microwave radiation, in contrast with gamma, X ray, and ultraviolet radiation, falls at the longer wavelength end of the electro-magnetic spectrum. It has wavelengths of approximately 1 mm to 1 m, a range that includes television and police radar wavelengths.

Sterilization by Microwave Oven:

A specialized microwave oven has recently become available that can be used to sterilize media in just 10 minutes. It has 12 pressure vessels, each of which holds 100 ml of medium. Microwave energy increases the pressure of the medium inside the vessels until sterilizing temperatures are reached.

Applications of Microwaves:

Microwave oven frequencies are tuned to match energy levels in water molecules. In the liquid state, water molecules quickly absorbs the microwave energy and than release it to surrounding materials as heat. The molecules are set into high-speed motion, and the heat of friction is transferred of foods, which become hot rapidly. Thus, materials that do not contain water, such as plates made of paper, china, or plastic, remain cool while the moist food on them becomes heated.

Limitations of Microwave Ovens:

Other than the heat generated, there is no specific activity against microorganisms.

For this reason the home microwave cannot be used to sterilize items such as bandages and glassware. Conduction of energy is metals leads to problems such as sparking, which makes most metallic items also unsuitable for microwave sterilization. Moreover, bacterial endospores, which contain almost no water, are not destroyed by microwaves.


A final form of radiation we shall consider is light energy. When concentrated by sophisticated devices, light energy forms a laser beam. The word laser is an acronym of light amplification by stimulated emission of radiation.

Advantage of Lasers

Recent experiments indicate that laser beams can be used to sterilize instruments and the air in operating rooms, as well as a wound surface. Microorganisms are destroyed in a fraction of a second, but the laser beam must reach all parts of the material to effect sterilization.



Caution should be observed in cooking foods in the home microwave oven. Geometry and differences in density of the food being cooked can cause certain regions to become hotter than other, sometimes leaving very cold spots. Consequently, to cook foods thoroughly in a microwave oven, it is necessary to rotate the items either mechanically or by hand. For example, pork roasts must be turned frequently and cooked thoroughly to kill any cysts of the pork roundworm Trichinella. Failure to kill such cysts could lead to the disease trichinosis, in which cysts of the worm become embedded in human muscles and other tissues. All experimentally infected pork roasts, when microwaved without rotation, showed live worm remaining in some portion at the end of standard cooking time.

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