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  Radiation

Radiation:

Radiation is energy transmitted via space. Solar radiation provides the light energy for photosynthesis and the heat produced enables drying and desiccation of materials and therefore control the microbes to some extent. Electromagnetic radiation including of light rays (i.e., visible light), x-rays, UV rays, gamma rays, and so on is the most significant in control of organisms. Radiation is explained by its wavelength (l) and measured in Angstrom (Å) units (1 um = 10,000 Å E; 1nm = 10 Å) and its energy in electron voltas (ev). The electromagnetic spectrum is described in figure shown below:

2007_radiation.jpg


                                                Figure: Electromagnetic spectrum of radiant energy

Radiation with more than 10ev energy such as gamma rays and X-rays ionize the molecules (i.e., ionizing radiation) by driving out electrons. Whenever irradiated with such rays cells discharge free hydrogen radical, hydroxyl radical and peroxides which causes intracellular damage in a variety of materials and therefore non-specific in their effect. This also generates less heat in the irradiated material and therefore termed as cold sterilization. This contains application in sterilization of heat sensitive substances and in food and pharmaceutical goods. X-rays are lethal to all forms of life since of their penetrating ability. Although their utilization in microbial control is limited as of its high production cost and complexity in use as they are given off on all directions from its source. Though these rays are broadly utilized to develop microbial mutants.

Ultra Violet (UV) radiation comprises rays of 150 to 3900 Å wave length, though UV rays of  wave length around 2650 Å possess highest  bactericidal  property.  Most of the UV lamps (i.e., germicidal lamps) emit UV rays of 2600 to 2700 Å and are employed in microbiological laboratories, aseptic filling rooms, hospital operating rooms, and in pharmaceutical industry where sterile materials are filled in vials and in food and dairy industries to control microbes on surfaces. UV rays contain less energy,very little penetrating power and do not cause ionization (i.e., non-ionizing radiation) though absorbed. Microorganisms on surfaces directly exposed to UV rays alone are damaged as a large part of such rays are filtered even by a thin glass. The UV light is also present in solar radiation (i.e., sun light) but most of the shorter wavelength UV rays get filtered by clouds and smoke of atmosphere and only rays of 2670 to 3500 Å wave lengths reach the earth’s surface. This demonstrates the limited degree of germicidal effect of sunlight.

 

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