P3 - X-rays and Ultraviolet

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  • P3 - X-rays and Ultraviolet
    • X-rays in medicine - EM waves.
      • X-ray images-used in hospitals for medical diagnosis-bone fractures  & dental problems. High frequency, short wavelength EM waves.
      • Affect photographic film same way as light, so they can be used to take photographs.
      • Can be formed electronically, using CCDs. They're silicon chips divided up into a grid of identical pixels. They detect X-rays & produce electronic signals which are used to form HQ images.
      • CT scans - Computerised axial tomography.  Produce HQ images of soft and hard tissue.
        • The x-ray tube and the detectors are rotated around during the scan.
        • Detailed images, diagnose complicated illnesses.
      • Can treat cancer. X-rays cause ionisation- high doses kill living cells. They have to be carefully focussed, and at the right dosage to kill the cancer cells, without damaging nomal cells
      • Radiographers need to take precaution to minimise their x-ray dose.  They wear lead aprons, stand behind a lead screen, or leave the room.
      • X-ray -  Clear images of bones and metal, but not a lot else.
    • Ultrasound - sound higher than a frequency of 20,000 Hz.
      • When a wave passes through media,  some of the wave is reflected off the boundary, and some is transmitted (pass through) and refracted - partial reflection.
      • You can point a pulse of ultrasound at an object, and wherever there are boundaries, some get reflected back.
        • The time  taken for the reflections to reach the detector, can be used to measure how far away the boundary is.
      • You  can use oscilloscope traces to find boundaries.
      • S = V x T
      • Used in medicine. Breaking down kidney stones and pre-natal scanning of a fetus.
      • Non-ionising. Images are typically fuzzy - harder to diagnose.

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