Irradiation, Contamination and Dose · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Touched by rays or by dust

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. A dental X-ray irradiates a patient. What happens when that machine switches off?

    • The patient keeps emitting the X-rays
    • The X-rays keep circling in the body
    • The exposure from that machine ends

  2. A loaf receives approved food irradiation to reduce germs. No radioactive material is added. Which description matches the treatment?

    • It received radiation from the beam
    • It received radioactive material from the beam
    • It gained radioactivity induced by the beam

  3. A patient swallows a radioactive tracer for a scan. It travels to an organ. What distinguishes this from a dental X-ray?

    • Only an outside beam has reached the body
    • Radioactive material is now inside the body
    • The organ has produced its own radioactive tracer

  4. A report gives an added effective dose of 3 mSv over a year and a background effective dose of 6 mSv over that year. How does the added dose compare? This is a numerical comparison, not a safety judgment.

    • Twice the stated background dose
    • Half the stated background dose
    • Equal to the stated background dose

  5. After radioiodine treatment, why does the treatment team give a patient hygiene instructions?

    • Body fluids can transfer radioactive material
    • Washing immediately stops all nuclear decay in the body
    • The treatment makes every nearby object radioactive

  6. Once a dental X-ray exposure ends, any damage it caused must also disappear.

    Circle one:   True   False

  7. Two suitable tracers have the same initial activity. Other factors are fixed, and both last long enough for a scan. Why can the tracer with the shorter half-life reduce later exposure?

    • Its material cannot damage any cells during the scan
    • Equal initial activity gives equal dose whatever the half-life
    • Its activity falls sooner after the scan

  8. Radioactive dust remains on a person's skin after an external X-ray machine is switched off. Why can exposure from the dust continue?

    • Its half-life restarts whenever the person moves away
    • The dust remains a source that can keep emitting
    • It always causes more damage than any external X-ray
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Touched by rays or by dust W1-mt_WyxR7ZVEhi-s1

  1. The exposure from that machine ends · The machine stops producing X-rays. It has not left a radioactive source in the patient.
  2. It received radiation from the beam · The beam irradiated the loaf. Approved treatment does not add radioactive material or induce radioactivity; naturally present radionuclides are a separate matter.
  3. Radioactive material is now inside the body · The tracer places a radioactive source inside the body. A dental X-ray uses a source outside the patient.
  4. Half the stated background dose · Both figures use mSv over the same year. Dividing 3 by 6 gives one half. Background is not a safety limit.
  5. Body fluids can transfer radioactive material · Body fluids can carry radioiodine to surfaces or other people. The patient follows the treatment team's specific instructions.
  6. False · Ending exposure stops further radiation from that machine. It does not undo damage that may have occurred.
  7. Its activity falls sooner after the scan · Under the stated conditions, the shorter half-life makes activity fall faster and can reduce later exposure. It does not make the tracer harmless.
  8. The dust remains a source that can keep emitting · The dust contains radioactive material that can keep emitting. Switching off a separate X-ray machine does not stop that source.
Worksheet · LightMySky