Explanation
(a) Fission: Nuclear reaction in which a heavy nucleus is bombarded with neutrons and split into approximate equal parts emitting neutrons and releasing large amounts of energy.
Fusion: Nuclear reaction between two light nuclei forming a heavier nucleus with the release of a large amount of energy.
(b) Advantages of Fusion over Fission:
(1)By - products are non-radioactive. (2) Easily achieved with lightest elements so that nuclear repulsion is easily overcome as nuclei approach each other. (3) Raw materials are cheaply available.
Why fusion is not normally used : Very high temperature is required to overcome coulomb repulsive forces between the two light nuclei. It is difficult to get materials that will withstand such high temperature. Mathematically,
\(T^{\frac{1}{2}} = \frac{0.693}{\lambda}\), where \(\lambda\) is the decay constant.
Decay constant = \(\frac{\text{no of atoms disintegrating per sec}}{\text{no of atoms in the source at that instant}}\)
Isotopes: Isotopes of an element are atoms which have the same proton numbers/atoms number but different nucleon numbers/mass number.
Decay scheme: \(^{238} _{92} U \to ^{234} _{90} Th + ^{4} _{2} He + Energy\)
\(^{234} _{90} Th \to ^{234} _{91} Pa + ^{0} _{-1} e + Energy\)
\(^{234} _{91} \to ^{0} _{-1} e + ^{234} _{92} + Energy\)
(d) Uses of radioisotopes:
(1) Radio therapy (2) Radio dating (3) Used as tracers and preservatives in agriculture.

