The **radioactive series** also called as **radioactive decay series** is the series of elements obtained by successive disintegration of a parent radioactive element to a non-radioactive stable element. The series of elements obtained from _{90}Th-232, _{92}U-235, and _{92}U-239 are natural radioactive series, while the series obtained from artificially prepared _{93}Np-237 is called radioactive series.

When a radioactive element emits α or β particles, the new daughter elements are formed and may have unstable nuclei. The daughter element further disintegrates by emitting α and β particles forming new elements. The process of disintegration is continued until a non-radioactive stable element is obtained. Thus, the formation of the stable nucleus from a radioactive element is not a one-step process.

There are four series of radioactive elements.

**Thorium (4n) Series****Uranium (4n+2) Series****Actinium (4n+3) Series****Neptunium (4n+1) Series**

## Thorium (4n) Series

It begins with the radioactive elements, Uranium-232 and ends with stable non-radioactive lead (Pb)-208. The mass number of all elements are integral multiple of 4.

## Uranium (4n+2) Series

The parent element, uranium-238, is used as its starting parent radioactive elements which undergo disintegration and form lead-206 as its final stable component. Since the mass number of all elements in this series gives a remainder of 2 when divided by 4, it is called the (4n+2) series, where n is an integer. It possesses the longest half-life.

## Actinium (4n+3) Series

The radioactive element uranium-235 converts into Lead-207, a stable element as the final product. Since the mass number of all elements in this series gives a remainder of 3 when divided by 4, it is called the (4n+3) series, where n is an integer.

## Neptunium (4n+1) Series

The elements in this series are not found in nature. It begins with Bismuth-200 and terminates into stable neptunium-237. The mass number of all elements in this series gives a remainder of 1 when divided by 4, hence is called the (4n+1) series.

## List of radioactive series

The various radioactive series with their starting element, end-stable elements, and the half-life is presented below:

Series | Name of Series | Starting Radioactive Element | Stable Non-Radioactive Element | Half-life of Starting Element |

4n | Thorium | _{90}Th-232 | _{82}Pb-208 | 1.3 ×10^{10} year |

4n+1 | Neptunium | _{94}Pu-241 | _{83}Bi-209 | 4.5 ×10^{9} year |

4n+2 | Uranium | _{92}U-238 | _{82}Pb-206 | 7.1 ×10^{8} year |

4n+3 | Actinium | _{92}U-239 | _{82}Pb-207 | 13.2 year |

## Radioactive Series Video

## References

- Atkins, P. (2010). Shriver & Atkins’ Inorganic Chemistry (5th or later Edition). Oxford University Press.
- Lee, J. D. (2008). Concise Inorganic Chemistry: Fifth Edition by J.D. Lee (Fifth edition). Oxford University Press.
- Arun Bahl, B. S. Bahl & G. D. Tuli,
*Essentials of Physical Chemistry*, S. Chand and Company Ltd., New Delhi, 2012.