7. Atomic, nuclear and particle physics

7. Atomic, nuclear and particle physics

7.1 – Discrete energy and radioactivity

Nature of science:

  • Accidental discovery: Radioactivity was discovered by accident when Becquerel developed photographic film that had accidentally been exposed to radiation from radioactive rocks. The marks on the photographic film seen by Becquerel probably would not lead to anything further for most people. What Becquerel did was to correlate the presence of the marks with the presence of the radioactive rocks and investigate the situation further.

Understandings:

  • Discrete energy and discrete energy levels

  • Transitions between energy levels

  • Radioactive decay

  • Fundamental forces and their properties

  • Alpha particles, beta particles and gamma rays

  • Half-life

  • Absorption characteristics of decay particles

  • Isotopes

  • Background radiation

Applications and skills:

  • Describing the emission and absorption spectrum of common gases

  • Solving problems involving atomic spectra, including calculating the wavelength of photons emitted during atomic transitions

  • Completing decay equations for alpha and beta decay

  • Determining the half-life of a nuclide from a decay curve

  • Investigating half-life experimentally (or by simulation)

7.2 – Nuclear reactions

Nature of science:

  • Patterns, trends and discrepancies: Graphs of binding energy per nucleon and of neutron number versus proton number reveal unmistakable patterns. This allows scientists to make predictions of isotope characteristics based on these graphs.

Understandings:

  • The unified atomic mass unit

  • Mass defect and nuclear binding energy

  • Nuclear fission and nuclear fusion

Applications and skills:

  • Solving problems involving mass defect and binding energy

  • Solving problems involving the energy released in radioactive decay, nuclear fission and nuclear fusion

  • Sketching and interpreting the general shape of the curve of average binding energy per nucleon against nucleon number

7.3 – The structure of matter

Nature of science:

  • Predictions: Our present understanding of matter is called the Standard Model, consisting of six quarks and six leptons. Quarks were postulated on a completely mathematical basis in order to explain patterns in properties of particles. Collaboration: It was much later that large-scale collaborative experimentation led to the discovery of the predicted fundamental particles.

Understandings:

  • Quarks, leptons and their antiparticles

  • Hadrons, baryons and mesons

  • The conservation laws of charge, baryon number, lepton number and strangeness

  • The nature and range of the strong nuclear force, weak nuclear force and electromagnetic force

  • Exchange particles

  • Feynman diagrams

  • Confinement

  • The Higgs boson

Applications and skills:

  • Describing the Rutherford-Geiger-Marsden experiment that led to the discovery of the nucleus

  • Applying conservation laws in particle reactions

  • Describing protons and neutrons in terms of quarks

  • Comparing the interaction strengths of the fundamental forces, including gravity

  • Describing the mediation of the fundamental forces through exchange particles

  • Sketching and interpreting simple Feynman diagrams

  • Describing why free quarks are not observed

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