(a) Define isotopes. (b) Mention two uses of radioactive tracers in each of the following areas: (\(\alpha\)) medicine (\(\beta\)) industry (\(\gamma\)) agr...

(a) Isotopes are atoms of the same element that have the same atomic number (same number of protons) but different mass numbers (different numbers of neutrons).

(b) Uses of radioactive tracers:

• (\(\alpha\)) Medicine: to locate tumours or study the functioning of organs (e.g. iodine-131 for the thyroid); to trace blood flow and detect blood clots or circulatory disorders.
• (\(\beta\)) Industry: to detect leaks in buried pipes carrying oil, water or gas; to measure the thickness of sheets (metal, paper, plastic) and monitor wear in engine parts.
• (\(\gamma\)) Agriculture: to study the uptake and movement of fertilisers by plants (e.g. phosphorus-32); to study how plants absorb water and nutrients and to induce useful mutations.

(c) Features of electromagnetic waves:

• They are transverse waves and travel through a vacuum at the speed of light (\(3\times10^{8}\,\text{m s}^{-1}\)).
• They consist of oscillating electric and magnetic fields at right angles to each other and to the direction of travel.
• They carry energy, are not deflected by electric or magnetic fields (uncharged), and can be reflected, refracted, diffracted and polarised.

(d) Components of a nuclear reactor and their functions:

• Fuel rods (e.g. uranium-235): provide the fissile material that undergoes fission to release energy.
• Moderator (e.g. graphite or heavy water): slows down the fast neutrons so that they can cause further fission.
• Control rods (e.g. boron or cadmium): absorb excess neutrons to control the rate of the chain reaction (and shut it down).
• Coolant (e.g. water, carbon dioxide gas): removes the heat produced in the core and carries it to the heat exchanger to raise steam. (A thick concrete/lead shield protects workers from radiation.)