AQA GCSE Physics 4.4.2 Atoms and Nuclear Radiation Exam Questions

About AQA GCSE Physics 4.4.2 Atoms and Nuclear Radiation

This AQA GCSE Physics section explains why unstable nuclei decay and what they emit. You need to compare alpha, beta and gamma radiation, write balanced nuclear equations, work with half-life from graphs and data, and distinguish radioactive contamination from irradiation. It is examined on Paper 1. Half-life calculations and nuclear equations appear in almost every series, and Higher tier students must also find the net decline as a ratio after a number of half-lives.

What you need to know

• Radioactive decay Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process. Activity is the rate at which a source decays, measured in becquerels (Bq). Count rate is the number of decays recorded each second by a detector such as a Geiger-Muller tube.
• Types of radiation Alpha (α): two neutrons and two protons (a helium nucleus). Beta (β): a high speed electron ejected from the nucleus as a neutron turns into a proton. Gamma (γ): electromagnetic radiation from the nucleus. A nucleus can also emit a neutron.
• Penetration, range and ionising power Alpha is stopped by paper or a few cm of air and is strongly ionising. Beta is stopped by a few mm of aluminium, travels about a metre in air, and is moderately ionising. Gamma is reduced by thick lead or concrete, travels far in air and is weakly ionising.
• Nuclear equations Alpha decay: mass number decreases by 4 and atomic number by 2. Beta decay: mass number unchanged, atomic number increases by 1. Gamma emission does not change mass or charge of the nucleus.
• Half-life The half-life of a radioactive isotope is the time it takes for the number of nuclei in a sample to halve, or the time for the count rate (or activity) from a sample to fall to half its initial level.
• Net decline (Higher tier only) Calculate the net decline, expressed as a ratio, after a given number of half-lives. After n half-lives the fraction remaining is (1/2)^n.
• Contamination and irradiation Radioactive contamination is the unwanted presence of materials containing radioactive atoms on or in other materials. Irradiation is exposing an object to nuclear radiation; the object does not become radioactive. Suitable precautions include gloves, tongs, shielding and keeping distance.

Common mistakes in 4.4.2 Atoms and Nuclear Radiation

• Saying beta particles come from the electron shells. They are electrons emitted from the nucleus when a neutron changes into a proton.
• In beta decay, changing the mass number. Only the atomic number changes (increases by 1).
• Saying an irradiated object becomes radioactive. Irradiation does not make the object radioactive; contamination involves radioactive atoms on or in it.
• Reading half-life from a graph at the wrong point. Find the time for the count rate to fall from any value to half that value, and subtract background radiation if told to.
• Saying radioactive decay can be predicted for individual nuclei. Decay is random; half-life only applies to large numbers of nuclei.

Try three 4.4.2 Atoms and Nuclear Radiation exam-style questions