Atomic Number: 2
Atomic Symbol: He
Atomic Weight: 4.002602
Melting Point: -457.96 F (-272.2 C)
Boiling Point: -452 F (-268.93 C)
Word origin: The word helium is derived from helios, the Greek word for the sun.
Discovery: The first evidence of helium was gathered during a solar eclipse in 1868 by Jules Cesar Janssen.
Properties of helium
Helium is only second to hydrogen as the most plentiful element in the universe. Helium is extracted from natural gas. All natural gas contains trace quantities of helium. [See Periodic Table of the Elements]
The helium content of Earth's atmosphere is about 1 part in 200,000. The majority of the planet’s supply of helium can be found in wells in Texas, Oklahoma and Kansas. A few helium extraction plants have existed outside of the United States, including Russia, Poland and India.
Helium plays a key role in the proton-proton reaction and the carbon cycle, which feed the energy of the sun and stars, and is especially prevalent in the hotter stars.
NASA's Lunar Reconnaissance Orbiter (LRO) has detected helium in the moon's wispy atmosphere.
There are a number of unique properties to helium, including the fact that it is the sole liquid that cannot be solidified by lowering its temperature, and that it stays liquid even at absolute zero at standard pressures.
Uses of helium
The energy necessary for the hydrogen bomb comes from the fusion of hydrogen into helium. It is also used as a cooling medium for nuclear reactors, as an inert gas shield for arc welding, as a gas for supersonic wind tunnels, and as a protective gas in growing silicon and germanium crystals and producing titanium and zirconium.
Helium has been used in cryogenic research due to the fact that at close to absolute zero, it has the lowest melting point of any element. Hydrogen has also been integral to the study of superconductivity.
There are a number of medical applications for liquid helium, including magnetic resonance imaging (MRI) and magnetic resonance elastography (MRE) to perform blood analysis to determine if a patient has cancer.
Pressuring liquid-fuel rockets is another recent use of helium, with an example being the Saturn rockets that were used on the Apollo lunar missions.
Divers and others who work under pressure use a mixture of helium and oxygen to create an artificial atmosphere to survive.
The Goodyear Blimp uses helium, and various government agencies have used blimps to detect low-flying cruise missiles, drug activity and to perform atmospheric research.
In a much less serious application, helium is widely used for filling balloons as it is safer than hydrogen.
There are seven known isotopes of helium: There are two forms of liquid helium (He-4): He-4I and He-4II, with a sharp transition point at 2.174K. Above this temperature, He-4I is a normal liquid, but He-4II is unlike any other identified substance below that temperature. It expands on cooling, is an enormous conductor of heat.
(Source: Los Alamos National Laboratory)