What happens when a positron (the antimatter equivalent of an electron) collides with a neutron? Antimatter reacting with matter annihilates an equal quantity of both, but how can an equal amount be annihilated here when the positron is a fundamental particle (of mass 1/2000th that of the neutron), and so is the neutron?
Because the neutron is made of quarks, and the positron is a fundamental particle. You must be careful with your definitions---anti-electrons (positrons) anihilate with electrons. Anti-protons anihilate with protons, and anti-neutrons anihilate with neutrons.
An inverse beta decay process is possible, in which a proton is formed from the neutron and positron.
The idea is that one can divide things up to a point, just like Democritus (?) thought a long time ago. So, what are atoms made of---protons, neutrons, and electrons. Protons and neutrons are made of quarks, and quarks are fundamental---quarks are made of quarks. Probably plus a neutrino to conserve lepton number?
Because their always is something smaller the greek named the atom meaning literally "the smallest indivisible particle of matter" A lot has changed in 2000 years but then again a lot wil change in the next 2000. I'm sure their that in the end (or near it) things will pop up so exotic that they don't even have dimension in sence of (LXWXH)
Personally I think that quarks are made of strings, mostly because I am writing a PhD dissertation on this subject. However, there are no experiments which tell us that we should believe this.
It's possible that quarks, and even leptons, have some sub-structure. However, the energies needed to check such things are far beyond the capabilities of any existing or planned particle accelerator.
