Tuesday, 22 April 2014 10:07





Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. The atomic nuclei of elements beyond atomic number 83 are very heavy and unstable. The particles of these heavy nuclei are not held together as firmly as those of the atomic nuclei of smaller atoms; therefore, the nuclei of heavier atoms give out some of their particles in an attempt to attain stable form. This process is accompanied by emission of energy also. If radiations emanating from a radioactive substance are passed through a magnetic field, they get affected. From this behaviour it was found that radiations coming from radioactive materials are of three kinds-

• Alpha radiations are composed of two protons and two neutrons, the alpha particle is a nucleus of the element helium. Because of its very large mass and its charge, it has a very short range. It is not suitable for radiation therapy since its range is less than a tenth of a millimeter inside the body.

• Beta radiations: They consist of a stream of electrons. Each of which has a unit negative charge and a negligible mass. These rays have a high velocity equal to about 93% that of light.

• Gamma radiations: It is composed of electromagnetic rays. They are of very short wavelength of the order of 10-8 cm. It is the most useful type of radiation for medical purposes, but at the same time it is the most dangerous because of its ability to penetrate large thicknesses of material.

Nuclear Fission

It is a process in which bombardment of a nucleus by fast moving neutrons which results in its break up in two smaller nuclei of almost equal mass with the liberation of large amount of energy.

The sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation.

Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously.

Uranium is the principle element used in nuclear reactors and in certain types of atomic bombs. The specific isotope used is 235U. When a stray neutron strikes a 235U nucleus, it is at first absorbed into it. This creates 236U. 236U is unstable and this causes the atom to fission. The fissioning of 236U can produce over twenty different products. However, the products' masses always add up to 236.

The chain fission reactions are of two types-

(1) Controlled Nuclear Fission (ex. Nuclear reactor)

(2) Uncontrolled Nuclear Fission (ex. Nuclear bomb)

Nuclear Fusion

Nuclear Fusion is the process that powers the sun and the stars. It is the reaction in which two atoms of hydrogen combine together, or fuse, to form an atom of helium. In the process some of the mass of the hydrogen is converted into energy. The easiest fusion reaction to make happen is combining deuterium (or “heavy hydrogen) with tritium (or "heavy-heavy hydrogen") to make helium and a neutron. The fusion of one kilogram of D-T fuel releases thousands of times more energy than burning one kilogram of coal and has no associated greenhouse gas emissions. Deuterium is plentifully available in ordinary water. Tritium can be produced by combining the fusion neutron with the abundant light metal lithium. Thus fusion has the potential to be an inexhaustible source of energy.

Conditions for Nuclear Fusion

To make fusion happen, the atoms of hydrogen must be heated to very high temperatures (100 million degrees) so they are ionized (forming a plasma) and have sufficient energy to fuse, and then be held together i.e. confined, long enough for fusion to occur. The sun and stars do this by gravity

Last Updated on Wednesday, 23 April 2014 06:58