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This is a diagram of an infrared space telescope, that needs a cold mirror and instruments. One instrument needs to be even colder, and it has a cryocooler. The instrument is in region 1 and its cryocooler is in region 3 in a warmer region of the spacecraft. (see MIRI (Mid-Infrared Instrument) or James Webb Space Telescope)
A medium-sized dewar is being filled with liquid nitrogen by a larger cryogenic storage tank. Note the ice covering the cold piping. This is because air is condensing and freezing out of the air onto the supercold metal pipes.

In physics, cryogenics is the production and behaviour of materials at very low temperatures.

It is not well defined at what point on the temperature scale refrigeration ends and cryogenics begins. A gas may be cryogenic if it can be liquefied at or below −150 °C (123 K; −238 °F).[1]

The U.S. National Institute of Standards and Technology considers cryogenics as involving temperatures below −180 °C (93 K; −292 °F). The normal boiling points of helium, hydrogen, neon, nitrogen, oxygen, and normal air are below −180 °C.

The Freon refrigerants, hydrocarbons, and other common refrigerants have boiling points above −180 °C.[2][3]

Discovery of superconducting materials has raised interest in reliable, low cost methods of producing high temperature cryogenic refrigeration. The term "high temperature cryogenic" means temperatures from above the boiling point of liquid nitrogen, −195.79 °C (77.36 K; −320.42 °F), up to −50 °C (223 K; −58 °F).[4]

Cryogenicists use the Kelvin or Rankine temperature scale, both of which measure from absolute zero, rather than more usual scales such as Celsius which measures from the freezing point of water at sea level or Fahrenheit with its zero at an arbitrary temperature.


  • Magnetic resonance imaging is an important machine for hospital diagnosis. It shows internal damage to soft tissues, and is very important in brain surgery.
  • Nuclear magnetic resonance is used for the physical and chemical properties of atoms.
  • Rocket cryongenic fuel is used as a propellant.
  • Cryogenics create the temperatures needed to store or transport large amounts of food without it deteriorating.
  • Many physical experiments need cryogenic temperatures.
  • Underground cables transmitting electricity are made much more efficient if they are cooled to cryogenic temperatures.