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On Earth it is relatively rare—5.2 ppm by volume in the atmosphere.Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei.Although the extraction process, using low-temperature gas liquefaction, was not developed in time to be significant during World War I, production continued.Helium was primarily used as a lifting gas in lighter-than-air craft.Following a suggestion by Sir Richard Threlfall, the United States Navy sponsored three small experimental helium plants during World War I.The goal was to supply barrage balloons with the non-flammable, lighter-than-air gas.
A well-known but minor use is as a lifting gas in balloons and airships.
Helium is a chemical element with symbol He and atomic number 2.
It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table.
In 1903, large reserves of helium were found in natural gas fields in parts of the United States, which is by far the largest supplier of the gas today.
Liquid helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners.