Helium-4

  • helium-4, 4he
    he-4 atom.png
    general
    symbol4he
    nameshelium-4, he-4
    protons2
    neutrons2
    nuclide data
    natural abundance99.999863%
    half-lifestable
    isotope mass4.002602 u
    spin0
    binding energy28300.7 kev
    isotopes of helium
    complete table of nuclides
    picture of a diffuse gray sphere with grayscale density decreasing from the center. length scale about 1 angstrom. an inset outlines the structure of the core, with two red and two blue atoms at the length scale of 1 femtometer.
    the helium atom. depicted are the nucleus (pink) and the electron cloud distribution (black). the nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case.

    helium-4 (4
    he
    ) is a stable isotope of the element helium. it is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. its nucleus is identical to an alpha particle, and consists of two protons and two neutrons.

    alpha decay of heavy elements in the earth's crust is the source of most naturally occurring helium-4 on earth, produced after the planet cooled and solidified. while it is also produced by nuclear fusion in stars, most helium-4 in the sun and in the universe is thought to have been produced by the big bang, and is referred to as "primordial helium". however, primordial helium-4 is largely absent from the earth, having escaped during the high-temperature phase of earth's formation.

    helium-4 makes up about one quarter of the ordinary matter in the universe by mass, with almost all of the rest being hydrogen.

    when liquid helium-4 is cooled to below 2.17 kelvins (−271.17 °c), it becomes a superfluid, with properties that are very unlike those of an ordinary liquid. for example, if superfluid helium-4 is kept in an open vessel, a thin film will climb up the sides of the vessel and overflow. in this state and situation, it is called a "rollin film". this strange behavior is a result of the clausius–clapeyron relation and cannot be explained by the current model of classical mechanics, nor by nuclear or electrical models – it can only be understood as a quantum-mechanical phenomenon. the total spin of the helium-4 nucleus is an integer (zero), and therefore it is a boson (as are neutral atoms of helium-4). the superfluid behavior is now understood to be a manifestation of bose–einstein condensation, which occurs only with collections of bosons.

    it is theorized that at 0.2 k and 50 atm, solid helium-4 may be a superglass (an amorphous solid exhibiting superfluidity).[1][2][3]

    helium-4 also exists on the moon and—as on earth—it is the most abundant helium isotope.[citation needed]

  • the helium-4 atom
  • stability of the 4he nucleus and electron shell
  • see also
  • external links
  • references

Helium-4, 4He
He-4 atom.png
General
Symbol4He
Nameshelium-4, He-4
Protons2
Neutrons2
Nuclide data
Natural abundance99.999863%
Half-lifestable
Isotope mass4.002602 u
Spin0
Binding energy28300.7 keV
Isotopes of helium
Complete table of nuclides
Picture of a diffuse gray sphere with grayscale density decreasing from the center. Length scale about 1 Angstrom. An inset outlines the structure of the core, with two red and two blue atoms at the length scale of 1 femtometer.
The helium atom. Depicted are the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case.

Helium-4 (4
He
) is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists of two protons and two neutrons.

Alpha decay of heavy elements in the Earth's crust is the source of most naturally occurring helium-4 on Earth, produced after the planet cooled and solidified. While it is also produced by nuclear fusion in stars, most helium-4 in the Sun and in the universe is thought to have been produced by the Big Bang, and is referred to as "primordial helium". However, primordial helium-4 is largely absent from the Earth, having escaped during the high-temperature phase of Earth's formation.

Helium-4 makes up about one quarter of the ordinary matter in the universe by mass, with almost all of the rest being hydrogen.

When liquid helium-4 is cooled to below 2.17 kelvins (−271.17 °C), it becomes a superfluid, with properties that are very unlike those of an ordinary liquid. For example, if superfluid helium-4 is kept in an open vessel, a thin film will climb up the sides of the vessel and overflow. In this state and situation, it is called a "Rollin film". This strange behavior is a result of the Clausius–Clapeyron relation and cannot be explained by the current model of classical mechanics, nor by nuclear or electrical models – it can only be understood as a quantum-mechanical phenomenon. The total spin of the helium-4 nucleus is an integer (zero), and therefore it is a boson (as are neutral atoms of helium-4). The superfluid behavior is now understood to be a manifestation of Bose–Einstein condensation, which occurs only with collections of bosons.

It is theorized that at 0.2 K and 50 atm, solid helium-4 may be a superglass (an amorphous solid exhibiting superfluidity).[1][2][3]

Helium-4 also exists on the Moon and—as on Earth—it is the most abundant helium isotope.[citation needed]