Helium, the second element in the periodic table, is the second-most abundant element in the universe after hydrogen. It is a noble gas that is unreactive (because of its filled outer electronic shell), colorless, and odorless. Helium is found in great abundance in many stars, such as the Sun, and is an important component in both the proton-proton reaction and the carbon cycle, which account for the energy of the Sun and stars. The energy released as hydrogen is fused into helium and is the source of the power contained in a hydrogen bomb. Under 25 atmospheres of pressure, helium has a boiling point of -268.9°C (-52.1°F or 4.22K) and a melting point of -272.2°C (-458°F or 0.95K). At this temperature, slightly above absolute zero, helium is transformed into helium II, superfluid helium, a liquid with unique properties.
French astronomer Pierre Janssen (1824-1907) first obtained evidence for the existence of helium during the solar eclipse of 1868 in India. During this eclipse he detected a new yellow line in the solar spectrum very close to that of the sodium D-line. Shortly thereafter it was recognized as an element not then known on earth, and the British scientists, Sir Joseph N. Lockyer (1836-1920) and Sir Edward Frankland (1825-1899), suggested the name helium, from the Greek helios meaning sun, for the substance. Later, in 1895, British chemist Sir William Ramsay (1852-1916) isolated helium from cleveite, a uranium-bearing mineral, while simultaneously Swedish chemist Per Teodor Cleve (1840-1905) and Langlet did the same thing. In 1907 Ernest Rutherford and T. Royds demonstrated that alpha particles are helium nuclei. Two of the naturally occurring isotopes of helium on Earth are helium-3, now thought to be a product of the radioactive decay of the tritium isotope of hydrogen, and helium-4, the most common form, thought to come from the radioactive alpha emitters in rocks.
Superfluid helium has unique physical properties in that it has no exact freezing point and its viscosity is apparently zero. It passes readily through cracks and through minute pores. This form of helium was first discovered in 1908, but nearly 25 years passed before any explanations concerning its properties were published. It is one of the few phenomena supposed to show quantum effects on a large scale. The properties of superfluid helium are attributed to it behaving like a boson gas in that all of the atoms occupy the same energy level and can be described in terms of a single wave function and as such is known as a Bose-Einstein condensate.
All of the helium on Earth at this time is produced through radioactive decay. Natural gas is the major commercial source of helium. Helium is produced from radioactive alpha emitters in rocks and then seeps into natural gas where it is found at about 0.4%. Most of the helium produced commercially is extracted from natural gas found in the United States. At the current rate of use the United States will exhaust its helium supply by the year 2016.
Helium has a number of uses in various scientific fields, in manufacturing, and in other forms of business. Because helium's boiling point is close to absolute zero it is used in cryogenic research as well as studies concerning superconductivity. It is used in balloons since it is safer than hydrogen and will not burn. Helium's use as an inert gas shield for arc welding and growing silicon and germanium crystals as well as in titanium and zirconium production is widely known. In its liquid form it is used to cool nuclear reactors. Helium mixed with oxygen is used as an artificial atmosphere for divers and others working under pressure because it reduces the chances of suffering from the bends.
This is the complete article, containing 614 words
(approx. 2 pages at 300 words per page).
