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Radioactive Disintegration Series


** A number of elements such as uranium and radium are unstable. Their atomic nucleus breaks of its own accord to form a smaller atomic nucleus of another element. The protons and neutrons in the unstable nucleus regroup to give the new nucleus. This causes the release of excess particles and energy from the original nucleus, which we call radiation.

** The elements whose atomic nucleus emits radiation are said to be radioactive.

** The spontaneous breaking down of the unstable atoms is termed radioactive disintegration or radioactive decay.

** The disintegration or decay of unstable atoms accompanied by emission of radiation is called Radioactivity

Radioactive Disintegration Series

** A radioactive element disintegrates by the emission of an α- or β- particle from the nucleus to form a new ‘daughter element’. This again disintegrates to give another ‘daughter element’.

** The process of disintegration and formation of a new element continues till a non-radioactive stable element is the product.

** The whole series of elements starting with the parent radioactive element to the stable end product is called a Radioactive Disintegration Series. Sometime, it is referred to as a Radioactive Decay Series or simply Radioactive Series.

** All the natural radioactive elements belong to one of the three series:
(1) The Uranium Series
(2) The Thorium Series
(3) The Actinium Series

The Uranium Series

** It commences with the parent element uranium-238 and terminates with the stable element lead-206.

** It derives its name from uranium-238 which is the prominent member of the series and has the longest half-life.

** The Uranium series is illustrated in this Figure .

The Thorium Series

** It begins with the parent element thorium-232 and ends with lead-208 which is stable.

** This series gets its name from the prominent member thorium-232.

The Actinium Series

** It starts with the radioactive element uranium-235. The end-product is the stable element lead-207.

** This series derives its name from the prominent member actinium-227.

The Neptunium Series

** This series consists of elements which do not occur naturally.

** It commences with neptunium 237 and terminates at bismuth-200.

** It derives its name from the prominent member neptunium-237.

Reference: Essentials of Physical Chemistry /Arun Bahl, B.S Bahl and G.D. Tuli / multicolour edition.

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