Beta decay is a type of radioactive decay that yields a beta particle. A beta particle can be either be an election (e-) or a positron (e+), a positron being the antiparticle of a an electron.
In β- decay, we see a neutron turning in to a proton. It does this by converting one of it’s down (d) quarks to an up (u) quark. Neutrons consist of an up quark and two down quarks (udd) and protons have two up quarks and one down quarks (udu). The below Feynman diagram shows how this happens.
At the bottom left you see a neutron with an up quark and two down quarks. When one of it’s down quarks changes to an up, it emits a weak negative boson (W-). The W- decays rather quickly because it’s not stable. It decays in to an election and a election antineutrino. (sorry I can’t find a good way to show an election antineutrino in html)
n → p + e- + ¯ve
In β+ decay we see an proton turn in to a neutron by emitting a positron (e+) and an election neutrino. This is a little different because a neutron weighs more than a proton. So we have to add energy in to our system to account for the addition mass.
Energy + p → n + e+ + ve
I can’t find a Feynman diagram to show this one. Maybe I’ll just edit this post later.