Helium

Helium has two nuclear protons and two electrons in a neutral atom; common helium-4 also contains two neutrons. It is a noble gas, normally monatomic and weakly reactive. Helium-3 and helium-4 have different nuclei, making isotopic identity relevant when comparing low-temperature behaviour.

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Solar observations in 1868 revealed a yellow spectral line associated with an unfamiliar element. Researchers later confirmed helium in gases released from terrestrial minerals. The sequence illustrates how spectral evidence can identify distant matter before corresponding material samples become available for laboratory comparison and study.

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Alpha particles released by radioactive decay are helium nuclei and can become helium atoms after gaining electrons. Some terrestrial helium accumulates in geological deposits associated with natural gas. Its cosmic abundance does not make extraction from Earth’s air economical, so supplies depend on suitable deposits and recovery arrangements.

References: [1]

At atmospheric pressure helium liquefies near 4.2 K, and colder helium-4 can become superfluid. The Large Hadron Collider uses closed helium circuits to maintain superconducting magnets. Cooling, heat transport and material properties operate together, while superconductivity still depends on the conductor and its operating conditions.

References: [2] [1]