Helium

Occurrence

Abundance

Helium is the second most abundant element in the known Universe after hydrogen and constitutes 23% of all elemental matter measured by mass even though there are 8 times as many hydrogen atoms as helium ('elemental matter' does not include dark matter or dark energy, which together may account for 96% of the Universe). It is concentrated in stars, where it is formed from hydrogen by the nuclear fusion of the proton-proton chain reaction and CNO cycle. This so-called 'hydrogen burning' process provides the energy stars need to shine. According to the Big Bang model of the early development of the Universe, the vast majority of helium was formed in the first three minutes after the Big Bang. Its widespread abundance is seen as part of the evidence that supports this theory.

Related Topics:
Universe - Hydrogen - Matter - Mass - Atom - Dark matter - Dark energy - Star - Nuclear fusion - Proton-proton chain reaction - CNO cycle - Big Bang - Theory

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However, in the Earth's atmosphere, the concentration of helium by volume is only 5.2 parts per million at sea level and up to 15 miles (24 km), largely because most helium in the Earth's atmosphere escapes into space due to its inertness and low mass. There is a layer in the heterosphere (a part of the Earth's upper atmosphere) at 600 miles (about 1000 km) where helium is the dominant gas (although the total pressure is very low). Helium is the 71st most abundant element in the Earth's crust where it is found in 8 parts per billion (109). Helium only makes up 4 parts per trillion (1012) in seawater.

Related Topics:
Earth's atmosphere - Sea level - Atmosphere - Space - Heterosphere - Earth's crust - Seawater

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Essentially all helium on Earth is a result of radioactive decay of elements such as uranium and radon. A type of radiation called alpha particles are made of two protons and two neutrons, which also makes them helium-4 nuclei. These +2 positive ions easily gain the two electrons needed to make complete helium atoms. In this way an estimated 0.5 ft³ of helium is produced from every cubic mile of the Earth's crust (3.4 L/km3) per year . This decay product is found in minerals of uranium and thorium, including cleveites, pitchblende, carnotite, monazite and beryl. There are also small amounts in mineral springs, volcanic gas and meteoric iron.

Related Topics:
Radioactive decay - Uranium - Radon - Radiation - Alpha particle - Proton - Neutron - Ion - Electron - Decay product - Thorium - Cleveite - Pitchblende - Carnotite - Monazite - Beryl - Springs - Volcanic - Iron

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Production

Helium in the crust is produced by the radioactive decay of uranium and thorium which are present in varying concentrations throughout the crust, but helium migrates and can collect in certain areas when conditions are right. Thus the greatest concentrations (trace amounts up to 7% by volume) of helium on the planet are in natural gas fields, from which most commercial helium is derived. As of 2002 over 100 million m³ (3.5 billion ft³) were produced annually with 80% of production from the United States, 16% from Algeria, and most of the rest from Russia. The principal source for U.S. production is the natural gas wells of the U.S. states of Texas, Oklahoma, Arizona and Kansas. Helium is also produced in Canada, Poland, the People's Republic of China, and Qatar.

Related Topics:
Uranium - Thorium - Natural gas - As of 2002 - United States - Algeria - Russia - U.S. state - Texas - Oklahoma - Arizona - Kansas - Canada - Poland - People's Republic of China - Qatar

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Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen and hydrocarbons such as methane) from natural gas in order to extract gaseous helium (the general process is called fractional distillation). The resulting crude helium gas is subjected to a process of purification in which almost all of the remaining nitrogen and other gases are precipitated out of the mixture through successive exposures to lowering temperatures. Activated charcoal is used as a final purification step, usually resulting in 99.995% pure Grade A helium. The principal impurity in Grade A helium is neon.

Related Topics:
Nitrogen - Hydrocarbon - Methane - Fractional distillation - Activated charcoal - Neon

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Diffusion of crude natural gas through special semi-permeable membranes and other barriers is another method to recover and/or purify helium. Helium can also be synthesized by bombardment of lithium-6 or boron with high-velocity neutrons in a nuclear reactor to produce He-4 and tritium. The tritium decays with a half life of 12.5 years to produce He-3. This method of production, however, is not economically viable—at least for making normal commercial-grade helium. Fusion in exploding hydrogen bombs creates helium as well.

Related Topics:
Permeable - Lithium - Boron - Neutron - Nuclear reactor - Tritium - Half life - Hydrogen bomb

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