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Radiation: a Discussion

Radiation is a part of man’s environment. Man is exposed from two sources of radiation natural and man made.

Natural sources of radiation are cosmic rays internal rays like carbon-14 and Potassium-40, atmospheric and terrestrial. Man made sources of radiation are medical & dental X-rays, radioisotopes for treatment of killer disease like cancer, radioactive fall out from nuclear explosions. Miscellaneous man made radioactive sources are television sets, radioactive dial matches, luminous markers, isotope tagged products. They are too small a source of radiation to be significant at present.

Natural sources:

Man is exposed to radiation throughout life continuously. Cosmic rays originate in outer space and become weak as they pass through atmosphere. Generally a person is exposed to about 35mrad of radiation a year. At higher attitude of about 20 km cosmic radiation becomes important. A commercial jet pilot receives about 300mrad of radiation a year compare to normal 35mrad.

Terrestrial radiation: Radioactive elements like thorium, uranium, radium and radioactive isotopes are present in man’s environment e.g. soil, rocks, buildings. Man derives about 50mrad of radiation from terrestrial sources. Some areas like Kerala in India, rock formations contain uranium, where radiation exposure may be as high as 2000mrad per year. Radiation from radioactive gases like radon contribute about 2mrad of radiation per year.

Internal radiation: Man is exposed to internal radiation from radioactive materials stored in body tissues. These include minute quantities of uranium, thorium, radioactive isotopes of carbon(C14), Potassium(K40), strontium(Sr90). From these sources radiation is about 25mrad per year but it may be as high as 70 to 80. it is estimated that a person is exposed to about 0.1rad of radiation per year from natural sources.

Man made sources:

Man is exposed to man made sources of radiation in addition to natural sources.

X-ray: this is the largest source of man made radiation. Two groups of people are exposed to X-ray radiation, patients and radiologists & radio technicians and radiotherapists. When optimum radiographic techniques are used a single X-ray film can give more than 0.02rad.

Radioactive fallout:

Nuclear explosions release tremendous amount of energy in the form of heat, light, radiation and also it releases many radioactive substances like carbon (C14), iodine (I 131), cesium (Cs 137) and strontium (Sr 90). Cesium and strontium are very important because they are released in large quantities and their half lives are 30 years and 28 years respectively. They float for few years and due to air current the particles are distributed throughout the world. Miscellaneous sources contribute too small am out of radiation to be important.

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