= Alpha decay
{wiki}
Most of the <helium> in the Earth's atmosphere comes from alpha decay, since helium is lighter than air and naturally escapes out out of the atmosphere.
Wiki mentions that alpha decay is well modelled as a <quantum tunnelling> event, see also <Geiger-Nuttall law>.
As a result of that law, alpha particles have relatively little energy variation around 5 MeV or a speed of about 5% of the <speed of light> for any element, because the energy is inversely exponentially proportional to <half-life>. This is because:
* if the energy is much larger, decay is very fast and we don't have time to study the <isotope>
* if the energy is much smaller, decay is very rare and we don't have enough events to observe at all
\Video[https://www.youtube.com/watch?v=_f8zeEI0oys]
{title=<Quantum tunnelling> and the <Alpha particle> Paradox by <Physics Explained> (2022)}
{description=
* https://youtu.be/_f8zeEI0oys?t=796 George Gamow and Edward Condon proposed the <quantum tunnelling> explanation
* https://youtu.be/_f8zeEI0oys?t=1725 worked out example that predicts the <half-life> of <polonium-210> based on its emission energy
}