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Nuclear Decay Chemistry

February 11, 2013

It was observed that the mass of the protons and neutrons together is more than the mass of the nucleus.

Introduction to nuclear decay chemistry

This difference is called mass defect.So where is the mass going to?Is it just vanishing in the air?

No.The mass is converted to energy,It could also be emitted in the forms of decaying rays. Nuclei undergo decay if they are unstable.The mass defect found is conserved by means of mass of the decayed components.Einstein contributed to explain this difference to attributing it to the binding energy.Binding energy binds the protons of a nucleus together in the nucleus which would otherwise repel each other and would burst the nucleus.

This information was used to harness the binding energy by breaking the nuclei.

So nuclear fission was that reaction used in an atom bomb which used this tremendous energy.

Einstein gave the relationship by his  famous equation


where m is mass converted to energy and c is speed of light.

This fission reaction is accompanied by decays.

Every decaying element  is characterized by a decay constant.

Half life is time taken to reduce the decay activity by half of the original.

The relationship between the decay constant and half life is given by

2.30 log X0/X = kt
t1/2 = 2.303 / decay constant

Causes of nuclear decay

The unstable nucei would undergo fragmentation,giving rise to another unidentical element.When this happens ,the ‘excess’ items are thrown away as rays,which are nothing but compositions of neutrons,protons or electromagnetic radiations.

Now we can dicuss about nuclear radiation in following paragraphs.

These rays are named as alpha, beta and gamma as they were discovered progressively.

Types of nuclear decay

Alpha rays

They are nothing but Helium nuclei. They are represented by 2 protons and 2 neutrons.As a result the emission of an alpha particle would reduce the mass number by 4 and atomic number by 2. e.g.

23892U      ?      23490Th      +      42He

These particles don’t travel very far but are high in penetrating strength.They  are stopped by thin sheets or even air.As it passes through air,it goes on loosing energy,which is utilized to break atoms in air. A garunted source of it is the metal Americium.

 Beta rays

These are high energy particles. It is assumed that if an outsider neutron splits,it may split in a proton and electron.The electron may be emitted as beta ray,and the proton may increase the atomic number of the resulting  nuclei by one. e.g.

23490Th  ——-> 23491Pa      +        0-1e

Most commonly used source of beta particles is Strontium-90. It is used in treating different types of cancers.

Gamma rays

They are high energy electromagnetic waves.The emission doesn’t affect the mass or atomic number. As they bear high energy,they are dangerous to living things as the rays damage the living tissues.


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