6 ms·
> What is even the size of a proton? Just a layman but I think they usually define size via the halfway distance between the centers of two identical bound par
by dataflow 5y ago
> What is even the size of a proton?
Just a layman but I think they usually define size via the halfway distance between the centers of two identical bound particles. Not entirely sure what that would be in this case though, given helium-2 is unstable and helium-3 might give a different result. (?)
- gowld 5y agoProtons don't bind without neutrons mixed in.
- dataflow 5y agoThat's why I wrote He-2 is unstable, yes.
- vikingerik 5y agoThey do for a very short duration (10^-9 s.) Nuclear fusion happens by protons binding via the strong force, then one beta-decays into a neutron before the electromagnetic repulsion pushes them beyond the range of the strong force. The beta decay happens fast enough in 0.01% of proton-proton collisions.
- contravariant 5y agoAs far as I know the size in these discussions is some kind of scattering cross-section. So roughly it's just how likely you are to hit it / how precise you need to aim. I don't know the exact details of the definition though.
- davrosthedalek 5y agoThat's one way to determine the size. But the same thing pops up in spectroscopy.
- whatshisface 5y agoYou are right about the atomic radii often quoted in chemistry, but the sizes of subatomic particles are usually defined in ways related to their cross-sections.
- dataflow 5y agoCool to know, thanks!
- dr_dshiv 5y agoBut isn't the cross section dependent upon what is interacting with them? Like, my understanding is that the cross section of hafnium is massive with respect to neutron capture, but not with respect to photons.
- whatshisface 5y agoAlthough the size isn't simply the square root of the cross section, you've hit on a truth that you'd get different sizes if you were asking about the distributions of different things.