Phyisics Unit 3

Using X-rays ans Ultrasound
1. X-rays
  1. X-rays are part of the electromagnetic spectrum. They cause ionisation because they are high-frequency, high-energy waves
  2. X-rays are absorbed by dense materials like bone and metal, but pass through less dense material like paper and healthy tissues.
  3. X-rays are used :
    1. In industry, to examine materials without damaging them.
    2. In airports, to examine luggage for security reasons.
    3. In medicine, to diagnose medical conditions.
      1. Medical X-rays have enough energy to pass through all tissue except teeth and bones. If soft tissues absorb barium or iodine , they will absorb X-rays.
  4. CT or CAT scans combine many X-rays taken from slightly different positions to produce a 3D image.
  5. Cancer cells are killed using focused beams of X-rays.
  6. X-ray are detected using photographic film, or electronic detectores that turn X-rays into an electronic image on screen.
  7. X-ray ionise cells and increase the risk of cells becoming cancerous. The risk increases with exposure, so a single X-ray is unlikely to be harmful.
  8. People working with X-rays are protected using lead screens. Film badges monitor their exposure to X-rays.
2. Ultrasound
  1. Ultrasound is waves with a frequency above 20,000Hz ( to high for humans). Ultrasound travels at different speeds in different materials and tissues.
  2. Pules of ultrasound are used to measure distance inside material because they partially reflected at boundaries between different materials.
  3. The speed of ultrasound in material is known.
  4. The time for the pulses to reflect off the boundary and return to the detector is measured.
  5. Medical uses of ultrasound:
    1. Scanning fetuses to check development.
    2. Detecting and treating medical conditions such as kidney stones.
  6. A gel is smeared on skin before an ultrasound examination. This stops Pulses reflecting off the boundarys between skin and air.

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Phyisics Unit 3

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