(A Level) Radioactive decay

Learning objectives

Explain how the scatter in repeated count-rate readings shows that radioactive decay is random, and what it means for decay to be spontaneous.

Define the activity of a sample and its decay constant λ, and calculate activity from the number of undecayed nuclei using A = λN.

Define half-life and convert between half-life and decay constant using λ = 0.693/t½ (ln 2/t½).

Sketch exponential decay curves and use x = x₀e^(−λt) for activity, number of undecayed nuclei or measured count rate, plotting ln x against t to find λ from the gradient.