OxfordAQA International GCSE Physics 3.7 Nuclear Physics Exam Questions

About OxfordAQA International GCSE Physics 3.7 Nuclear Physics

Nuclear Physics in OxfordAQA International GCSE Physics starts with the structure of the atom, the evidence from alpha particle scattering and isotope notation. You then study random radioactive decay, background radiation, the properties of alpha, beta and gamma radiation, and how to balance nuclear equations. The separate Physics course adds half-life, contamination and irradiation, and how half-life affects the hazards and uses of isotopes. The section finishes with nuclear fission and chain reactions in reactors, and, for separate Physics, nuclear fusion. It links to space physics in 3.8. Examiners regularly set half-life graph questions and nuclear equations.

What you need to know

• The atom Atoms have a radius of about 10^-10 m; the tiny nucleus contains protons and neutrons and almost all the mass, with electrons around it. Alpha scattering by thin metal foil showed that most of the atom is empty space with a small, dense, positive nucleus.
• Isotopes and notation Atomic number is the number of protons; mass number is protons plus neutrons. Isotopes have the same number of protons but different numbers of neutrons. Atoms lose or gain outer electrons to form ions.
• Radioactive decay Unstable nuclei emit radiation to become more stable; decay is random and unaffected by chemical or physical conditions. Background radiation comes from the environment, space and sources such as medical X-rays.
• Alpha, beta, gamma Alpha is two protons and two neutrons: most ionising, stopped by paper, few cm in air. Beta is a fast electron formed when a neutron becomes a proton: stopped by a few mm of aluminium. Gamma is electromagnetic radiation: least ionising, reduced by thick lead or concrete.
• Nuclear equations Alpha decay lowers mass number by 4 and atomic number by 2. Beta decay leaves mass number unchanged and raises atomic number by 1. Mass and atomic numbers must balance on both sides.
• Half-life (separate Physics) The half-life is the time for half the unstable nuclei to decay, or for the count rate to halve. Contamination is unwanted radioactive material on or in an object; irradiation is exposure to radiation and does not make the object radioactive.
• Fission Uranium-235 (or plutonium-239) absorbs a neutron, splits into two smaller nuclei and releases two or three neutrons and energy. Control rods absorb neutrons so that on average one neutron per fission causes another. Radioactive waste is long lived and hard to dispose of.
• Fusion (separate Physics) Two light nuclei join to form a heavier nucleus, converting some mass into energy. Very high temperature and pressure are needed to overcome repulsion; fusion powers stars.

Common mistakes in 3.7 Nuclear Physics

• Saying irradiated food becomes radioactive. Irradiation does not make objects radioactive; contamination involves radioactive atoms being present.
• Saying beta particles come from the electron shells. A beta particle is emitted from the nucleus when a neutron turns into a proton.
• Forgetting to subtract the background count before finding a half-life. Correct the count rate for background first, then find the time for it to halve.
• Confusing fission with fusion. Fission splits a large nucleus; fusion joins small nuclei.
• Saying gamma is the most dangerous inside the body. Alpha is the most ionising, so it is most dangerous inside the body, while gamma is most penetrating.

Try three 3.7 Nuclear Physics exam-style questions