Page 27 - 12-phy-21 NUCLEAR PHYSICS

21. Nuclear Physics eLearn.Punjab

It may be remembered that the mass of both krypton and barium is less than that of the mass
of uranium. This nuclear reaction was different from hither to studied other nuclear reactions, in
two ways. First as a result of the breakage of the uranium nucleus, two nuclei of almost equal size
are obtained, whereas in the other nuclear reactions the difference between the masses of the
reactants and the products was not large. Secondly a very large amount of energy is given out in
this reaction.

“Such a reaction in which a heavy nucleus like that of uranium splits
up into two nuclei of roughly equal size along with the emission of
energy during the reaction is called fission reaction”.

Fission reaction of U235 can be represented by the equation

92

U235 +10 n →15461 Ba +92 Kr+310n+Q
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92

here Q is the energy given out in this reaction. By

comparing the total energy on the left side of the

equation with total energy on the right side, we

find that in the fission of one uranium nucleus

about 200 MeV energy is given out. It may be kept

in mind that there is no difference between the

sum of the mass and the charge numbers on both

sides of the equation. Fission reaction is shown in

Fig. 21.12 (a) and (b). Fission reaction can be easily (a)
explained with the help of graph of Fig. 21.4.This

graph shows that the binding energy per nucleon

is greatest for the middle elements of the periodic table and this binding energy per nucleon is a

little less for the light or very heavy elements

i.e., the nucleons in the light or very heavy

elements are not so rigidly bound.

For example the binding energy per nucleon

for uranium is about 7.7 MeV and the products

of the fission reaction of uranium, namely

barium and krypton, have binding energy of

about 8.5 MeV per nucleon.

Fig. 21.12 (b) Process of Fission reaction

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