The phenomenon of radioactivity was discovered by the French physicists Antoine Henri Becquerel. He found that, some substances emit rays and while working on a cloudy day, he discovered that uranium salts emits penetrating rays even without exposure to light.
Later on it was also found that several other elements like radium, polonium, thorium etc. also emitted such rays. This process of spontaneous emission of rays is called the radioactivity and substances showing this property are called radioactive substances. The radiations coming from radioactive materials are of three kinds- a-radiations, (3-radiations and y-radiations).
This phenomenon of radioactivity is very useful in several fields such as in medicines, carbon dating etc. In medical field isotope tracer techniques have bee used to locate the disordered part of the body and radioactive iodine has been used in thyroid complaints and in locating tumor. Radioactive phosphorous in the form of phosphate is used in the treatment of blood disorder.
One of the principal constituents of blood is hemoglobin in which there is a small amount of iron. By putting radioactive iron (Fe59) into hemoglobin and injecting this hemoglobin into the blood stream, measurements can be made of the rate at which blood circulates to different parts of the body. The radioactive phenomenon is also being used in finding the death of animal or plants by measuring the amount of carbon 6C14.
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There is a constant percentage of this radioactive isotope of carbon in the air which we breath. During life, animals and plants absorb this radio-active carbon and thus, the concentration of 604 reaches a standard value in all living things. But, after the animal or plants dies, the 6C4 undergoes decay. The half-life period of 6C14is 5570 years. With the lapse of time, radioactivity of 604 in the dead animal or plant therefore falls and by measuring, the amount of 6C14 it is possible to find when the death of animal has occurred.