A-Level Physics: Nuclear Structure and Decay Equations

What is inside the nucleus, and why do some nuclei change into others? This material covers the structure and instability part of A level nuclear physics: the evidence for the nucleus, the equations that describe radioactive decay, and the pattern that tells you which way an unstable nucleus will decay. It complements work on half-life and binding energy by concentrating on the nucleus itself and on the notation you must handle accurately in examinations.

The quiz (12 questions) opens with Rutherford's alpha-scattering experiment: what the observations were, what they showed about the nucleus, and why the apparatus was evacuated. You then calculate the distance of closest approach of a 5.0 MeV alpha particle to a gold nucleus by equating kinetic energy to electric potential energy, and explain why this gives only an upper limit for the nuclear radius. The central part is about decay equations written in full nuclide notation: the product of an alpha decay, choosing the correct beta-minus equation (with the antineutrino that conserves lepton number), the products of beta-plus decay in a PET tracer, electron capture with its neutrino, and counting the alpha and beta-minus decays in a whole decay chain from thorium to lead. The last questions cover the N–Z stability band and the decay mode expected for neutron-rich, proton-rich and very heavy nuclides, correcting a count rate for background radiation, the wavelength of a gamma photon from an excited nickel nucleus, and why technetium-99m is used as a medical tracer.

The flashcards (12 cards) give the general forms of the alpha, beta-minus, beta-plus and electron-capture equations, the closest-approach formula, and definitions of the N–Z graph, gamma emission, excited states, corrected count rate and the Rutherford conclusion.

The written work (8 questions) asks you to describe the Rutherford experiment and its conclusions, derive and evaluate a distance of closest approach, write and label three balanced decay equations, explain the shape of the N–Z graph and the decay modes on either side of it, describe how to measure and correct for background radiation, use the inverse-square law for gamma radiation with background included, explain nuclear energy levels using cobalt-60, and justify the choice of technetium-99m for medical imaging.

The content follows the nuclear physics section common to A level Physics specifications in England (for example AQA section 3.8.1, radioactivity). Constants are given in each question.

• Describe Rutherford scattering and explain how it shows a small, dense, positive nucleus
• Calculate a distance of closest approach and explain why it is an upper limit for nuclear radius
• Write balanced alpha, beta-minus, beta-plus and electron-capture equations with the correct neutrino or antineutrino
• Use the N–Z stability band to predict decay modes and work through decay chains
• Correct count rates for background radiation and relate gamma emission to nuclear energy levels

Practice material written by Zestly, based on the DfE GCE AS and A level subject content for physics (DFE-00356-2014): nuclear physics, radioactivity and nuclear instability.