Radioactivity

Atomic structure, nuclide notation, radioactive decay, types of radiation, half-life, uses and hazards.

SEC G3 Combined Science Physics component 2027
4 lessons

Before you begin

Some atoms have unstable nuclei that break down and give out radiation, at random and with nothing to trigger them. The lessons start with the structure of the atom, nuclide notation and isotopes, then describe radioactive decay and the alpha, beta and gamma radiation it produces. They finish with background radiation, half-life, and the uses and hazards of radioactivity.

Be comfortable with: positive and negative charge, because the nucleus and the radiations are charged, and reading graphs, for decay curves.

Learning goals

Describe atomic composition
Use proton number, nucleon number and isotope
Use and interpret nuclide notation
Explain random and spontaneous nuclear decay
Describe alpha, beta-minus and gamma radiation
Compare ionising effect and penetrating power
Explain background radiation
Use half-life in tables and decay curves
State radioactivity applications and hazards

Syllabus statements covered

describe the composition of an atom in terms of a positively charged nucleus (with protons and neutrons) and negatively charged electrons
use the terms proton (atomic) number Z, nucleon (mass) number A and isotope
use and interpret the term nuclide and use the nuclide notation ᴬZX
show an understanding that nuclear decay is a random and spontaneous process whereby an unstable nucleus loses energy by emitting radiation
show an understanding of the nature of alpha (α), beta (β), and gamma (γ) radiation (including ionising effect and penetrating power) [β-particles are assumed to be β– particles only]
show an understanding of background radiation
use the term half-life in simple calculations, which might involve information in tables or decay curves
state the applications (e.g. medical and industrial uses) and hazards of radioactivity.

Lessons

Work through them in order.

Practise and check

All practice for this topic

Topic reference

Quick reference

Radiation	What it is	Charge	Ionising effect	Stopped by
alpha, α	helium nucleus, 2 protons and 2 neutrons	+2	strong	paper, or a few cm of air
beta, β⁻	fast electron from the nucleus	−1	moderate	a few mm of aluminium
gamma, γ	electromagnetic radiation	0	weak	reduced by thick lead or concrete

Idea	Meaning
nuclide X with nucleon number A and proton number Z	Z = proton number; A = nucleon number; neutrons = A-Z
isotopes	same proton number, different nucleon numbers
half-life	the time for half the nuclei in a sample to decay; the activity halves too

Core knowledge to remember

An atom has a small positively charged nucleus, containing protons and neutrons, surrounded by negatively charged electrons.
Nuclear decay is a random and spontaneous process in which an unstable nucleus loses energy by emitting radiation.
Background radiation is always present, from natural sources such as rocks, radon gas and cosmic rays, and from artificial sources such as medical X-rays. Subtract it from count rates before working out a half-life.
Radioactivity is used in medicine and industry, for example to treat cancer, sterilise equipment and check the thickness of materials. Its radiation can damage living cells and cause cancer.

Common mistakes

Confusing proton number with nucleon number.
Saying isotopes have different numbers of protons.
Saying a single nucleus will decay after one half-life.
Forgetting to subtract background radiation from a count rate.
Saying gamma radiation is the most dangerous in every situation. Inside the body, alpha is the most harmful.