CCEA GCSE Physics 1.5 Atomic and Nuclear Physics Exam Questions

About CCEA GCSE Physics 1.5 Atomic and Nuclear Physics

Atomic and Nuclear Physics is the final topic of Unit 1 in CCEA GCSE Physics. It starts with how models of the atom developed from the plum pudding model to the Rutherford-Bohr model, using alpha particle scattering as evidence. You then need the properties of alpha, beta and gamma radiation, how to write nuclear decay equations, how to correct for background radiation and how to find half-life from data or a graph. The topic covers the uses and dangers of radioactivity, and nuclear fission and fusion as energy sources. Examiners commonly set half-life calculations, balanced decay equations and explanations of chain reactions.

What you need to know

• Atomic models Thomson's plum pudding model was replaced after Rutherford's alpha scattering experiment showed that most of the atom is empty space with a small, dense, positive nucleus. Bohr then placed electrons in fixed orbits (shells).
• Nuclear notation and isotopes The nucleus contains protons and neutrons. Atomic number Z = number of protons; mass number A = protons + neutrons. Isotopes have the same number of protons but different numbers of neutrons.
• Alpha, beta and gamma Alpha: helium nucleus (2 protons, 2 neutrons), most ionising, stopped by paper or a few cm of air. Beta: fast electron from the nucleus, stopped by a few mm of aluminium. Gamma: electromagnetic wave, least ionising, only reduced by thick lead or concrete.
• Decay equations Alpha decay: mass number falls by 4 and atomic number by 2. Beta decay: a neutron becomes a proton and an electron, so mass number is unchanged and atomic number rises by 1. Gamma emission does not change A or Z. Totals of A and Z must balance on both sides.
• Background radiation and safety Background radiation comes from rocks (radon gas), cosmic rays, food and medical uses. Subtract the background count from readings. Handle sources with tongs, keep them at a distance, store them in lead-lined boxes and minimise exposure time.
• Half-life Half-life is the time taken for half of the unstable nuclei in a sample to decay, or for the activity (count rate) to halve. Find it from a graph by reading the time for the count rate to fall to half of any starting value.
• Fission and fusion Fission: a uranium-235 nucleus absorbs a neutron, splits into two smaller nuclei and releases 2 or 3 neutrons and energy, which can cause a chain reaction controlled by control rods in a reactor. Fusion: light nuclei such as hydrogen join to form heavier nuclei, releasing energy in stars. It needs very high temperatures and pressures, which is why fusion reactors such as ITER are difficult to build.

Common mistakes in 1.5 Atomic and Nuclear Physics

• Saying beta particles are electrons from the electron shells. They are electrons emitted from the nucleus when a neutron changes into a proton.
• Forgetting to subtract background radiation before calculating half-life from count rates.
• Thinking half-life means the time for all the material to decay, or that after two half-lives none is left. After two half-lives a quarter remains.
• Confusing fission (splitting large nuclei) with fusion (joining small nuclei).
• Stating that gamma radiation is completely stopped by lead. It is only reduced; thick lead or concrete absorbs most of it.

Try three 1.5 Atomic and Nuclear Physics exam-style questions