Atoms, nuclei and radiation

Learning objectives

Explain how the pattern of α-particle scattering by thin gold foil shows that an atom has a very small, dense, positively charged nucleus, and describe the nuclear model of protons and neutrons with orbiting electrons.

Distinguish proton number Z from nucleon number A, write nuclides in the form ²³⁸₉₂U, and explain why isotopes of an element differ only in their number of neutrons.

Compare α-particles, β⁻-particles (electrons), β⁺-particles (positrons) and γ-radiation by what they are made of, their mass and their charge, and describe the positron as the antiparticle of the electron: equal mass, opposite charge.

Write balanced α- and β-decay equations in which nucleon number and charge are both conserved, and use the unified atomic mass unit u for the masses of particles and nuclei.

Explain why β-particles emerge with a continuous spread of energies while α-particles from one source have discrete energies, in terms of the antineutrino (β⁻ decay) or neutrino (β⁺ decay) that shares the energy released.