Q.
Consider one of fission reactions of ${ }^{235} U$ by thermal neutrons ${ }_{92}^{235} U +n \rightarrow{ }_{38}^{94} Sr +{ }_{54}^{140} Xe +2 n$. The fission fragments are however unstable and they undergo successive $\beta$-decay until ${ }_{38}^{94} Sr$ becomes ${ }_{40}^{94} Zr$ and ${ }_{54}^{140} Xe$ becomes ${ }_{58}^{140} Ce$. The energy released in this process is
[Given: $m\left({ }^{235} U \right)=235.439\, u , m( n )=1.00866\, u , m\left({ }^{94} Zr \right)\left.=93.9064\, u , m\left({ }^{140} Ce \right)=139.9055\, u , 1\, u =931\, MeV \right]$
Nuclei
Solution: