A worker at a nuclear waste facility handles two different radioactive isotopes. Isotope P is an alpha emitter with a long half-life. Isotope Q is a beta emitter with a short half-life. The worker is concerned about the hazards of both isotopes. Explain which isotope presents the greater long-term hazard if it were to contaminate the worker's skin, and which presents the greater short-term hazard if the worker were only irradiated by it from a distance. Justify your answer.

OCR A-Level Physics B: Advancing Physics (H557) — 6.2 Electric and magnetic fields · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Radioactive contamination occurs when radioactive atoms are unwantedly deposited on a material, whereas irradiation is when an object is simply exposed to radiation from a source without the source touching it.

Model answer (5 marks)

Isotope P (alpha emitter) presents the greater long‑term hazard if it contaminates the worker’s skin, because alpha particles are highly ionising and cause severe damage to cells when the source is in direct contact with tissue. The long half‑life of P means it remains strongly radioactive and continues to irradiate the skin for a long period.

Isotope Q (beta emitter) presents the greater short‑term hazard if the worker is only irradiated from a distance, because beta radiation is more penetrating than alpha radiation and can reach and ionise the worker’s body tissues from a distance. Q’s short half‑life means its activity falls off quickly, so it is less hazardous in the long term.

Examiner tips

  • Use the word ‘present’ to match the mark scheme wording.
  • Explain both ionising power and half‑life for each isotope.
  • Mention penetration ability for the short‑term part.
  • Keep answer to 5–6 lines to fit the 5 marks.

Common mistakes

  • Confusing contamination with irradiation – stating that alpha radiation is dangerous from a distance.
  • Forgetting to link the long half‑life of P to its long‑term hazard.
  • Claiming beta radiation is more ionising than alpha, which is incorrect.

Mark scheme (5 marks)

  1. Isotope P (alpha emitter) presents the greater long-term hazard if it contaminates the skin
  2. Because alpha particles are the most ionising, so cause the most damage to cells/tissue when the source is in direct contact with the skin
  3. The long half-life of Isotope P means it remains strongly radioactive / continues to irradiate the skin for a long period of time
  4. Isotope Q (beta emitter) presents less of a long-term hazard because its short half-life means its activity / radioactivity quickly dies down
  5. Isotope Q (beta emitter) presents the greater short-term hazard from irradiation at a distance because beta radiation is more penetrating than alpha and can reach and ionise the worker's body tissues from a distance

Key terms in this question

half-life

Related

More Electric and magnetic fields questions

▶ Try answering this question with AI marking (free) →