JEE Main & Advanced Physics Nuclear Physics And Radioactivity Nuclear Fission

(1) The process of splitting of a heavy nucleus into two lighter nuclei of comparable masses (after bombardment with a energetic particle) with liberation of energy is called nuclear fission.

(2) The phenomenon of nuclear fission was discovered by scientist Ottohann and F. Strassman and was explained by N. Bohr and J.A. Wheeler on the basis of liquid drop model of nucleus.

(3) Fission reaction of \[{{U}^{\mathbf{235}}}\]

\[_{92}{{U}^{235}}+{{\ }_{0}}{{n}^{1}}\to \ \underset{\text{(unstable nucleus)}}{\mathop{_{92}{{U}^{236}}}}\,\to {{\ }_{56}}B{{a}^{141}}+{{\ }_{36}}K{{r}^{92}}+{{3}_{0}}{{n}^{1}}+Q\]

(4) The energy released in \[{{U}^{\mathbf{235}}}\] fission is about 200 MeV or 0.8 MeV per nucleon.

(5) By fission of \[_{92}{{U}^{235}}\], on an average 2.5 neutrons are liberated. These neutrons are called fast neutrons and their energy is about 2 MeV (for each). These fast neutrons can escape from the reaction so as to proceed the chain reaction they are need to slow down.

(6) Fission of \[{{U}^{\mathbf{235}}}\] occurs by slow neutrons only (of energy about 1eV) or even by thermal neutrons (of energy about 0.025 eV).

(7) 50 kg of \[{{U}^{\mathbf{235}}}\] on fission will release \[\approx 4\times {{10}^{15}}J\]  of energy. This is equivalence to 20,000 tones of TNT explosion. The nuclear bomb dropped at Hiroshima had this much explosion power.

(8) The mass of the compound nucleus must be greater than the sum of masses of fission products.

(9) The \[\frac{\text{Binding energy}}{\text{A}}\] of compound nucleus must be less than that of the fission products.

(10) It may be pointed out that it is not necessary that in each fission of uranium, the two fragments \[_{56}Ba\] and \[_{36}Kr\] are formed but they may be any stable isotopes of middle weight atoms.

(11) Same other \[{{U}^{\mathbf{235}}}\] fission reactions are 

\[_{92}{{U}^{235}}+{{\,}_{0}}{{n}^{1}}\to {{\,}_{54}}X{{e}^{140}}+{{\,}_{38}}S{{r}^{94}}+\,{{2}_{0}}{{n}^{1}}\]

\[\to {{\,}_{57}}L{{a}^{148}}+{{\,}_{35}}B{{r}^{85}}+3{{\,}_{0}}{{n}^{1}}\]

\[\to \] Many more

(12) The neutrons released during the fission process are called prompt neutrons.

(13) Most of energy released appears in the form of kinetic energy of fission fragments.