Radioactive decay, half-life, uses and hazards

Repair the common break

Common misconception: A radioactive sample decays at a predictable instant for each nucleus.

Correct model: Individual decay is random and spontaneous while population activity follows statistical decay; interpret background, radiation properties and half-life together.

Worked transfer

If corrected activity falls from 800 to 200 Bq in 10 h, two half-lives have passed, so t½ = 5 h. Background must be subtracted before forming the ratio.

Guided practice

Explain why “A radioactive sample decays at a predictable instant for each nucleus.” fails. Then construct one example that correctly applies radioactive decay, half-life, uses and hazards.

Independent practice

A detector reads 920 counts min⁻¹ initially and 220 counts min⁻¹ after 12 h; background is 20 counts min⁻¹. Determine the half-life.

Return to the recorded repair plan when the explanation and application are secure enough to re-test.