Radioactive Decay Series

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The emission of a or b - particles from a radioactive element results in the function of new element called daughter element. If the daughter element still has unstable nucleus, it further disintegrates by emitting a or b - particle and produces a new daughter element. This process of successive disintegration continues till the end product, is an element with stable nucleus. This series of spontaneous changes that take place starting from a radioactive element till the formation of a non-radioactive end product is called radioactive disintegration series.

There are four decay series distinguished by whether the mass numbers are divided by 4 or whether when divided by four, there are remainders of 1, 2 or 3.

It must be noted that in natural radioactive series, the changes in mass numbers are produced by the emission of a - particles only because emission of b - particles do not bring about any change in mass number.

The first natural series to be discovered is uranium - 238 series. It involves fourteen separate steps, eight of which involve a - emission whereas six involve b - emission. The overall process is written as

This uranium 238 series is called the (4n + 2) series. If we divide the mass number of uranium (238) by 4, it gives a remainder equal to 2. the mass number of each nuclide of the uranium series will give a remainder equal to 2 when divided by four. It means that the mass numbers of various nuclides of uranium series can be represented by formula (4n + 2) where n is an integer.

4n series

(4n + 1) series

This is also called neptunium series. It is an artificial series starting with

(4n + 3) series

This is also called Actinium series starts with