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Natural Radioactive Decay

March 18, 2013

Introduction to natural radioactive decay

Often we hear the term radioactive?What is it?

Atoms are composed of nucleus in the centre, which is consisting of neutrons and protons.

Usually the number of neutrons is same. In some cases the number of neutrons is slightly more..

Sometimes an element would contain more than one type where in the number of neutrons would be different for each type.

Such atoms with same number of protons but different number of neutrons are isotopes.

e.g.  1H1 1H2 and 1H3 called hydrogen, deuterium and tritium .The number of neutrons is 1, 2 and 3 respectively.

Natural radioactive decay

Nuclear stability is the function of ratio of neutron to proton.

If the number of neutrons is higher than is required for stability of the nucleus, the nucleus becomes unstable.

In order to gain stability, it would try to convert this extra mass of neutrons into sub-particles which are thrown out of the atom. This is done to achieve stability.

When this happens naturally it is called as natural radioactive decay.Over 60 radionuclides are found naturally and classified as primordial and cosmogenic.

They are found in water, air and soil too.

These particles are observed as radiation and hence this process is called radioactivity. It was discovered accidentally.

There are 3 major types of natural radioactive decays.

Alpha,beta and gamma decay

The alpha particle is having two protons and four neutrons. The atomic number decreases by 2 and the mass no. by 4 after the decay of an alpha particle.

238^92U  → 234^90Th + Alpha particle


Similarly the atomic number increases by one after the emission of a beta particle.

90234Th ———->  91234Pa + Beta

Gamma emissions

High frequency electromagnetic waves, however don’t change the atomic or mass number

Besides these, there are other minor radiations too.


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