X-ray Facts

  • X-rays are a form of electromagnetic radiation, as are radio waves, microwaves, visible light and ultraviolet. They all travel as waves, but have different wavelengths.
  • X-ray waves are much shorter and more energetic than visible light waves. X-rays are invisible because their waves are too short for our eyes to see.
  • X-rays are made when negatively charged particles called electrons are fired at a heavy plate made of the metal tungsten. The plate bounces back X-rays.
  • Even though they are invisible to our eyes, X-rays register on photographic film.
  • X-rays are so energetic that they pass through some body tissues like a light through a net curtain.
  • To make an X-ray photograph, X-rays are shone through the body. The X-rays pass through some tissues and turn the film black, but are blocked by others, leaving white shadows on the film.
  • Each kind of tissue lets X-rays through differently. Bones are dense and contain calcium, so they block X-rays and show up white on film. Skin, fat, muscle and blood let X-rays through and show up black on film.
  • X-ray radiation is dangerous in high doses, so the beam is encased in lead, and the radiographer who takes the X-ray picture stands behind a screen.
  • X-rays are very good at showing up bone defects. So if you break a bone, it will probably be X-rayed.
  • X-rays also reveal chest and heart problems.
  • X-rays are electromagnetic rays whose waves are shorter than ultraviolet rays and longer than gamma rays.
  • X-rays in space may be produced by very hot gases well over 1 million °C.
  • X-rays are also made when electrons interact with a magnetic field in synchrotron radiation.
  • X-rays cannot get through Earth’s atmosphere, so astronomers can only detect them using space telescopes such as ROSAT.
  • X-ray sources are stars and galaxies that give out X-rays.
  • The first and brightest X-ray source found (apart from the Sun) was the star Scorpius X-1, in 1962. Now tens of thousands are known, although most are weak.
  • The remnants of supernovae such as the Crab nebula are strong sources of X-rays.
  • The strongest sources of X-rays in our galaxy are X-ray binaries like Scorpius X-1 and Cygnus X-1. Some are thought to contain black holes.
  • X-ray binaries pump out 1000 times as much X-ray radiation as the Sun does.
  • X-ray galaxies harboring big black holes are powerful X-ray sources outside our galaxy.

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