Helium-4
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General | |
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Spin | 0 |
Binding energy | 28295.7 keV |
Isotopes of helium Complete table of nuclides |
Helium-4 (4
He
) is a
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
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 helium-4 atom
The helium atom is the second simplest atom (hydrogen is the simplest), but the extra electron introduces a third "body", so its wave equation becomes a "three-body problem", which has no analytic solution. However, numerical approximations of the equations of quantum mechanics have given a good estimate of the key atomic properties of helium-4, such as its size and ionization energy.
The size of the 4He nucleus has long been known to be in the order of magnitude of 1
Stability of the 4He nucleus and electron shell
The nucleus of the helium-4 atom has a type of stability called
For example, the stability and low energy of the electron cloud of helium causes helium's chemical inertness (the most extreme of all the elements), and also the lack of interaction of helium atoms with each other (producing the lowest melting and boiling points of all the elements).
In a similar way, the particular energetic stability of the helium-4 nucleus, produced by similar effects, accounts for the ease of helium-4 production in atomic reactions involving both heavy-particle emission and fusion. Some stable helium-3 is produced in fusion reactions from hydrogen, but it is a very small fraction, compared with the highly energetically favorable production of helium-4. The stability of helium-4 is the reason that hydrogen is converted to helium-4, and not deuterium (hydrogen-2) or helium-3 or other heavier elements during fusion reactions in the Sun. It is also partly responsible for the alpha particle being by far the most common type of baryonic particle to be ejected from an atomic nucleus; in other words, alpha decay is far more common than cluster decay.
The unusual stability of the helium-4 nucleus is also important cosmologically. It explains the fact that, in the first few minutes after the
All heavier elements—including those necessary for rocky planets like the Earth, and for carbon-based or other life—thus had to be produced, since the Big Bang, in stars which were hot enough to fuse elements heavier than hydrogen. All elements other than hydrogen and helium today account for only 2% of the mass of atomic matter in the universe. Helium-4, by contrast, makes up about 23% of the universe's ordinary matter—nearly all the ordinary matter that is not hydrogen (1H).
See also
References
- S2CID 3222218.
- ^ "Press release: Supersolid or superglass? Cornell researchers study a strange state of matter in helium - Cornell Chronicle".
- S2CID 119261743.
- ^ "cold cathode gauges: Topics by Science.gov". www.science.gov.
- ^ "Final Report Cold Cathode Gauge Experiment" (PDF). ntrs.nasa.gov.
- S2CID 4297697.
- PMID 33505036.
External links
- Superfluid Helium-4 Interactive Properties
- Tur, Clarisse (2009), "DEPENDENCE OF s-PROCESS NUCLEOSYNTHESIS IN MASSIVE STARS ON TRIPLE-ALPHA AND 12
C
(α, γ)16
O
REACTION RATE UNCERTAINTIES", The Astrophysical Journal, 702 (2): 1068–1077,S2CID 118483505