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3.2.6Stoichiometry

X-Rays — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 5 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5Properties of X-Rays

3.2.6 X-Rays
Short wavelength
  • X-rays have very short wavelengths and very high frequencies, so each wave carries a large amount of energy.
Ionising
  • X-rays can remove electrons from atoms, which can damage DNA and cells.
Absorption
  • They are absorbed strongly by bone and metal, but they pass largely through healthy soft tissue.
Photographic effect
  • They darken photographic film in the same way as visible light, which allows an image to be recorded.

Part 2 of 5Taking an X-ray Image

1
The patient is positioned so that the X-ray beam passes through the body part being examined.
2
X-rays are absorbed by bone or teeth, which casts a shadow on the detector behind them.
3
X-rays passing through soft tissue reach the flat-panel detector or the photographic film.
4
The detector produces an image that shows bones or teeth clearly against the surrounding tissue.

Part 3 of 5Medical Uses

Medical Uses
Contrast media
  • Substances such as barium absorb X-rays strongly, so organs such as the digestive tract show up on the image.
CT scans
  • Rotating X-ray tubes and detectors build cross-sectional and three-dimensional images of the body.
X-ray therapy
  • Shorter-wavelength X-rays are used to kill cancer cells, with metal filters limiting exposure to healthy tissue.
Engineering
  • X-rays are also used to find cracks inside metal components, which is important for safety inspections.

Part 4 of 5Worked Example

Question

  • An X-ray has a wavelength of 1.0 × 10⁻¹⁰ m.
  • Calculate its frequency, using a wave speed of 3.0 × 10⁸ m/s.

  1. Rearrange the wave equationf = v ÷ λ
  2. Substitutef = (3.0 × 10⁸) ÷ (1.0 × 10⁻¹⁰)
  3. Calculatef = 3.0 × 10¹⁸ Hz

Answer f = 3.0 × 10¹⁸ Hz.

Part 5 of 5Exam Checklist & Tips

3.2.6 – Key Points for the Exam

  • X-ray Ionising electromagnetic radiation with a very short wavelength and high frequency.
  • Ionising radiation Radiation with enough energy to remove electrons from atoms.
  • Contrast medium A substance that absorbs X-rays strongly, used to make organs visible.
  • CT scan A computerised X-ray technique that builds cross-sectional images of the body.
  • Absorption The transfer of an X-ray's energy to the material it passes through.

Common Mistakes

  • Saying X-rays are absorbed by soft tissue more than by bone.
  • Saying CT scans use gamma rays, when they use X-rays.
  • Entering 10⁻¹⁰ incorrectly on a calculator, which gives an answer with the wrong power of ten.
  • Assuming X-rays are harmless in medical imaging, when they are ionising and exposure must be kept as low as possible.

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