31 March 2011

Differences between fission and fusion reaction

Products are radioactive
and fission fragment are dangerous.
Fusion product is non-radioactive and is not dangerous environmentally acceptable source.
There will be total contamination of the surrounding medium due to radioactivity of various products of fission.
No fatal contamination of the surrounding medium.
A bombarding particle (slow neutron) is necessary to initiate the fission. There is no condition on the temperature of the fissible fuel. The fissible isotopes are initially at rest.
No bombarding particle is required. There is a threshold temperature. The temperature should be of the order of 108 K to produce controlled fusion reaction. The fusionable isotopes are with vigourous thermal motion.
Fast neutrons are released.
Nature of the ejected particle depends upon the type of thermonuclear reaction.
Probability depends upon the nuclear cross-section for slow neutrons.
Probability depends upon the temperature and density of plasma.
Fuel is in either solid or liquid state.
Fuel is in plasma state.
Fuel can be stored for any length of time.
Fuels cannot be stored so easily as no container can exist in solid state such very high temperature. For that magnetic mirrors, by which the plasma is isolated from its surroundings are employed.
Sum of the masses of the fission products should be less than the mass of the fissible isotope.
Sum of the masses of the fusionable isotopes should be greater than the compound nucleus formed on fusion. (m<50)
Fission fuels are costly production and preparation of them are not so easy.
Fusion fuels are available in plenty in nature. They are cheap and inexhaustible.
The reaction can be made self sustained. Chain reaction is possible.
Chain reaction is not possible under ordinary conditions. To sustain reaction energy must be provided to fuel material continuously i.e., the temperature of the fuel material must be maintained.