Helium II cannot be boiled because it has high thermal conductivity (high ability to conduct heat).
Helium-7 and helium-8 are "hyperfragments" that are created in certain nuclear reactions.
In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4 has almost no viscosity at temperatures near absolute zero, a phenomenon now called superfluidity.
Helium produced before 1945 was about 98 percent pure (2 percent nitrogen), which was adequate for airships.
Extreme conditions are also needed to create the small handful of helium compounds, which are all unstable at ordinary temperatures and pressures.
Nearly all helium on Earth is a result of radioactive decay.
A total of 200,000 cubic feet (5,700 mі) of 92 percent helium was produced in the program even though only a few cubic feet (less than 100 liters) of the gas had previously been obtained.
Helium, however, is unusual in that its isotopic abundance varies greatly depending on its origin.
Helium is used for many purposes that take advantage of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, and inertness.
The boiling and melting points of helium are the lowest among the elements.
Helium (chemical symbol He, atomic number 2) is a minor component of the Earth's atmosphere, but it is the second most abundant element in the universe and second lightest of all known elements.
Helium is the second most abundant element in the known universe, after hydrogen, constituting 23 percent of the elemental mass of the universe.
The rate of expansion decreases below the lambda point until about 1 K is reached; at which point expansion completely stops and helium I starts to contract again.
Equal mixtures of liquid helium-3 and helium-4 below 0.8 K will separate into two immiscible phases (two phases that do not mix) due to their dissimilarity (in terms of quantum statistics).
The nucleus of helium-3 contains two protons and one neutron, while that of helium-4 contains two protons and two neutrons.
The concentration of helium in the Earth's crust is 8 parts per billion; in seawater, it is only 4 parts per trillion.
Helium-7 also emits a beta particle, as well as a gamma ray.
Following a suggestion by Sir Richard Threlfall, the U.S. Navy sponsored three small experimental helium production plants during World War I.
Gaseous helium is colorless, odorless, tasteless, and nontoxic.
Once it has been cooled below this temperature, helium can be liquefied through expansion cooling.
The index of refraction of helium (ratio of speed of light in helium to that in a vacuum) is closer to unity than any other gas.
Like other cryogenic liquids, helium I boils when heat is added to it.
Extraplanetary material, such as lunar and asteroid regolith (loose material covering solid rock), have trace amounts of helium-3 from being bombarded by solar winds.
Helium I has a gas-like refractive index of 1.026, which makes its surface so hard to see that floats of Styrofoam are often used to show where the surface is.
Researchers use helium to study materials at very low temperatures, in a field called cryogenics, and in helium dating of radioactive rocks and minerals.
Helium was primarily used as a lifting gas in lighter-than-air craft.
The greatest concentrations of helium on our planet are in natural gas, from which most commercial helium is derived.
Helium II will escape from a vessel that is not sealed by creeping along the sides until it reaches a warmer region, where it evaporates.
When a surface extends past the level of helium II, the helium II moves along the surface, seemingly against the force of gravity.
In 1908, Dutch physicist Heike Kamerlingh Onnes was the first to liquefy helium by cooling the gas to below 1 Kelvin (K).
At normal temperatures, helium heats up when allowed to expand freely; but below about 40 K (Kelvin), it cools during free expansion.
On March 26, 1895, British chemist William Ramsay isolated helium on Earth by treating the mineral cleveite with mineral acids.
Helium is chemically unreactive under all normal conditions.
The helium-4 nucleus, consisting of two protons and two neutrons, is unusually stable.
Helium was also vital in the Manhattan Project that produced the atomic bomb.
Helium use in the United States in 1965 was more than eight times the peak wartime consumption.
Solid helium requires a temperature of 1–1.5 K (about ?272 °C or ?457 °F) and about 26 standard atmospheres (2.6 MPa) of pressure.
Based on this theory, the abundance of helium serves as a test of cosmological models.
The principal impurity in such helium is neon.
Helium II is a superfluid, a quantum-mechanical state of matter with strange properties.
Containers of helium gas at 5 to 10 K should be treated as if they have liquid inside.
Helium-6 decays by emitting a beta particle and has a half life of 0.8 second.
In 1945, a small amount of 99.9 percent helium was produced for welding use.
When heat is introduced, it moves through helium II in the form of waves, at 20 meters per second at 1.8 K, in a phenomenon called second sound.
The resulting crude helium gas is purified by successive exposures to low temperatures, by which almost all the remaining nitrogen and other gases are precipitated out of the mixture.
The different formation processes of the two stable isotopes of helium produce the differing isotope abundances.
Activated charcoal is used as a final purification step, usually resulting in 99.995 percent pure helium.
The shortest-lived isotope is helium-5, with a half-life of 7.6Ч10?22 second.
In 1925, the U.S. government set up the National Helium Reserve at Amarillo, Texas, with the goal of supplying military airships in time of war and commercial airships in peacetime.
Below its boiling point of 4.21 K and above a temperature of 2.1768 K (called the "lambda point" for helium), the helium-4 isotope exists in a normal, colorless liquid state, called helium I.
By 1949, commercial quantities of Grade A 99.995 percent helium were available.
Superfluid helium leaks through and increases the pressure, causing liquid to fountain out of the container.
The thermal conductivity of helium II is greater than that of any other known substance, a million times that of helium I and several hundred times that of copper.
Below the lambda point, liquid helium begins to exhibit very unusual characteristics, in a state called helium II.
In 1907, Ernest Rutherford and Thomas Royds demonstrated that an alpha particle (emitted by radioactive materials) is a helium nucleus.
The voice of a person who has inhaled helium temporarily sounds high-pitched, resembling those of the cartoon characters Alvin and the Chipmunks (although their voices were produced by shifting the pitch of normal voices).
Given that helium has a lower boiling point than any other element, it can be extracted from natural gas by liquefying nearly all the other elements in the mixture, at low temperature and high pressure.
The isotope helium-3 also has a superfluid phase, but only at much lower temperatures.
In 1972, the same phenomenon was observed with helium-3, by American physicists Douglas D. Osheroff, David M. Lee, and Robert C. Richardson.
That same year, chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, independently isolated helium from cleveite.
It is He-4, with two protons, two neutrons and two electrons, making up well over 99.99% of the helium on earth.
It was observed that the atoms of elements,having a completely filled outermost shell show little chemical activity. In other words their combining capacity is 0. Of these inert elements, the helium atom has 2 electrons in its outermost shell and all other elements have atoms with 8 electrons in the outermost shell.Jun 1, 2013