Katrina+Fuller+MASC

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 * Helium** is the [|chemical element] with [|atomic number] 2 and an atomic weight of 4.002602, which is represented by the [|symbol] **He**. It is a colorless, odorless, tasteless, non-toxic, [|inert] [|monatomic] [|gas] that heads the [|noble gas] group in the [|periodic table]. Its [|boiling] and [|melting] points are the lowest among the elements and it exists only as a gas except in extreme conditions. Next to [|hydrogen], it is the second most abundant element in the universe, and accounts for 24% of the elemental mass of our galaxy.======

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An unknown yellow [|spectral line] signature in sunlight was first observed from a [|solar eclipse in 1868] by French astronomer [|Pierre Janssen]. Janssen is jointly credited with the [|discovery of the element] with [|Norman Lockyer], who observed the same eclipse and was the first to propose that the line was due to a new element which he named helium. In 1903, large reserves of helium were found in the [|natural gas fields] in parts of the United States, which is by far the largest supplier of the gas.======

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Helium is used in [|cryogenics] (its largest single use, accounting for about a quarter of production), the cooling of [|superconducting magnets], particularly the main commercial application in [|MRI] scanners. Helium's other industrial uses as a pressurizing and purge gas, and a protective atmosphere for [|arc welding] and processes (such as growing crystals to make [|silicon wafers]), account for half of its use. Economically minor uses, such as lifting gas in balloons and [|airships] are popularly known.[|[2]] As with any gas with differing density from air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice. In scientific research, the behavior of two fluid phases of helium-4, helium I and helium II, is important to researchers studying [|quantum mechanics] (in particular the phenomenon of [|superfluidity]) and to those looking at the effects that temperatures near [|absolute zero] have on [|matter] (such as [|superconductivity]).======

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Helium is the second lightest element and is the second most [|abundant] in the observable [|universe], being present in the universe in masses more than 12 times those of all the heavier elements combined. Its abundance is also similar to this in our own [|Sun] and [|Jupiter]. This is due to the very high binding energy (per [|nucleon]) of helium-4 with respect to the next three elements after helium ([|lithium], [|beryllium], and [|boron]). This helium-4 binding energy also accounts for its commonality as a product in both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and is believed to have been formed during the [|Big Bang]. Some new helium is being created currently as a result of the [|nuclear fusion] of hydrogen in stars greater than 0.5 solar masses.======

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On Earth, the lightness of helium has caused its evaporation from the gas and dust cloud from which the planet condensed, and it is thus relatively rare—0.00052% by volume in the atmosphere. What helium is present today has been mostly created by the natural [|radioactive decay] of heavy radioactive elements ([|thorium] and [|uranium]), as the [|alpha particles] that are emitted by such decays consist of helium-4 [|nuclei]. This [|radiogenic] helium is trapped with [|natural gas] in concentrations up to 7% by volume, from which it is extracted commercially by a low-temperature separation process called [|fractional distillation].======