(a) Explain the terms nuclear fission and nuclear fusion.
(b) State two advantages of fusion over fission and explain briefly why, in spite of these advantages, fusion is not normally used for the generation of power.
(c) (^{238}{92} U) is a long half- life alpha emitter and decays to thorium Th which, in turn decays by beta emission with a small decay constant to an isotope of protactinium Pa. The protactinium decay scheme of (^{238}{92} U ) as stated above.
(d) State three uses of radioisotopes.
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.