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This doubly charged ion has been made by accelerating the helium hydride ion to 900 keV, and firing it into argon. It only has a short life of 4 ns. [70] H 2 He + has been made and could occur in nature via H 2 + He + → H 2 He +. [70] H 3 He + n exists for n from 1 to over 30, and there are also clusters with more hydrogen atoms and helium. [73]
Francis Aston had also recently shown that the mass of a helium atom was about 0.8% less than the mass of the four hydrogen atoms which would, combined, form a helium atom (according to the then-prevailing theory of atomic structure which held atomic weight to be the distinguishing property between elements; work by Henry Moseley and Antonius ...
Whereas the carbon–helium-ion bond breaks spontaneously and immediately to yield a carbocation, bonds of other elements to helium are more stable. For example, molecular tritium T 2 or tritium-hydrogen HT. On decay, these form a stable helium hydride ion [HeH] + (respectively [3 HeT] + or [3 HeH] +), which is stable enough to persist. This ...
As a side effect of the process, some carbon nuclei fuse with additional helium to produce a stable isotope of oxygen and energy: 12 6 C + 4 2 He → 16 8 O + γ (+7.162 MeV) Nuclear fusion reactions of helium with hydrogen produces lithium-5, which also is highly unstable, and decays back into smaller nuclei with a half-life of 3.7 × 10 −22 s.
As a result, there is little mixing of fresh hydrogen into the core or fusion products outward. In higher-mass stars, the dominant energy production process is the CNO cycle, which is a catalytic cycle that uses nuclei of carbon, nitrogen and oxygen as intermediaries and in the end produces a helium nucleus as with the proton–proton chain. [22]
Illustration of a proton–proton chain, from hydrogen forming deuterium, helium-3, and regular helium-4. Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. [1] Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.
The majority of these occur within stars, and the chain of those nuclear fusion processes are known as hydrogen burning (via the proton–proton chain or the CNO cycle), helium burning, carbon burning, neon burning, oxygen burning and silicon burning. These processes are able to create elements up to and including iron and nickel.
In stars between 4 and 11 solar masses, the 16 O already produced by helium fusion in the previous stage of stellar evolution manages to survive the carbon-burning process pretty well, despite some of it being used up by capturing 4 He nuclei. [1] [8] So the result of carbon burning is a mixture mainly of oxygen, neon, sodium and magnesium. [3] [5]
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