(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 advanta...

Answer Details

(a) Nuclear fission and nuclear fusion

Nuclear fission is the splitting of a heavy nucleus (such as uranium-235) into two lighter nuclei of comparable mass, together with the release of neutrons and a large amount of energy.

Nuclear fusion is the joining together of two light nuclei (such as hydrogen isotopes) to form a heavier nucleus, with the release of a large amount of energy.

(b) Advantages of fusion over fission, and why it is not normally used

Advantages:

• Fusion releases far more energy per unit mass of fuel.
• Its fuel (isotopes of hydrogen) is cheap and abundant, and the products are not highly radioactive, so there is little radioactive waste.

Why it is not normally used: fusion requires extremely high temperatures and pressures (millions of kelvin) to force the positively charged nuclei together against their electrostatic repulsion. No ordinary vessel can contain matter at such conditions, so a controlled, sustained, energy-yielding fusion reaction is very difficult to achieve and maintain.

(c) Decay scheme of \(^{238}_{92}\text{U}\)

Uranium-238 emits an alpha particle to become thorium-234:

\[ ^{238}_{92}\text{U} \;\rightarrow\; ^{234}_{90}\text{Th} + ^{4}_{2}\text{He} \]

Thorium-234 then emits a beta particle to become protactinium-234:

\[ ^{234}_{90}\text{Th} \;\rightarrow\; ^{234}_{91}\text{Pa} + ^{0}_{-1}e \]

(In alpha emission the mass number falls by 4 and the atomic number by 2; in beta emission the mass number is unchanged while the atomic number rises by 1.)

(d) Three uses of radioisotopes

• Medical: diagnosis and treatment (e.g. tracers, cobalt-60 for cancer therapy).
• Industrial: detecting leaks in pipes and measuring thickness of materials.
• Dating: carbon-14 dating of fossils and archaeological samples.