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Chapter 7.2 Radioactive disintegration (Radioactivity and Nuclear Physics)

Chapter 7.2 Radioactive disintegration (Radioactivity and Nuclear Physics)

Category: N/A Level: 3

The number of atoms disintegrated per second at any instant is directly proportional to the number of radioactive atoms actually present in the sample at that instant. Therefore, the rate of disintegration is governed by an exponential law. Moreover, it implies that the number of atoms that break up at any instant is not affected by environmental factors (like temperature, pressure, chemical combination, etc.)

Half-life of a radioactive element: According to the radioactive decay law, N=〖N_0  e〗^(-λt) , an infinite time is required for the radioactivity to disappear completely. All radioactive elements are same in this respect. Hence, in order to compare one radioactive element with another, a term half-life is often used. The half-life of a radioactive element is defined as the time that it takes for one half of the atoms of that substance to disintegrate into another nuclear form (Fig. 5 a, b). These can range from mere fractions of a second, to many billions of years. Moreover, the half-life of a particular radionuclide is unique to that radionuclide. For example, the half-life of radium is 1620 years. This means that it takes 1620 years for one-half of a given quantity of radium to change into its daughter product radon. In another 1620 years, ½ of the remainder would have disintegrated leaving ¼ of the original amount behind (Fig. 5 c). 













In radioactive disintegration, the original atoms transform to new atoms of new element. These new atoms are also radioactive leading to a long chain of different radioactive atoms in the form of a series (Fig. 6). The transformations go on until an inactive, i.e., stable substance is reached. In a radioactive series, any two adjacent elements may be considered as parent and daughter, the former being that which by its own decay produces the later.