EINSTEIN’S MASS ENERGY EQUATION  
according
to Einstein theory of relativity "Mass and Energy are inter convertable".
Einstein established a relation between mass and energy known as "Einstein’s Mass Energy Equation". 

E
= mc^{2}



where
E = Energy m = Mass C = Velocity of light (3x10^{8} m/sec) 

Define nuclear fission and explain fission chain reaction.  
DEFINITION
OF FISSION


"The
process in which a heavy nucleus in broken into two lighter nuclei
with the release of energy is called Nuclear Fission." OR The disintegration of a heavy nucleus after capturing neutron with the release of energy is called "Nuclear Fission." In one fission of _{92}u^{235} nucleus, about three neutrons are obtained. 

FISSION
IN _{92}u^{235}


In 1939,Hann and Stressman discovered that fission can be produced by bombarding _{92}u^{235} with slow neutrons. When _{92}u^{235 }is bombarded with neutron, it is broken down into two lighter nuclei and about 200Mev energy is released in this process.  
EQUATION
OF FISSION


_{0}n^{1}+_{92}u^{235}
è _{92}u^{236}
è _{56}Ba^{144}+_{36}Kr^{90}+3_{0}n^{1}+energy


Along with the fission products i.e. barium and krypton, three neutrons are also obtained.  
COLLISION
GEOMETRY


Fission
reaction in uranium can be explained by the following schematic diagram.


FISSION
CHAIN REACTION


In one fission of _{92}u^{235} nucleus, about three neutrons are obtained. These fast moving neutrons undergo successive collision with the other _{92}u^{235} nuclei. As more and more nuclei are broken by the neutrons, more and more neutrons are obtained and an uncontrolled fission process is started which is referred to as FISSION CHAIN REACTION. If it is not controlled, then all the _{92}u^{235} atoms are broken and a large amount of energy is produced. An interesting fact which must be noted down is that no fission chain reaction will take place if the amount of uranium is less than a certain mass known as CRITICAL MASS.  
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