Can protons change into neutrons outside the nucleus?

Protons are stable and do not decay for at least [math]10^{35}[/math] years. But if they absorb energetic particles in the right combination (e.g. electron and anti-neutrino), one could change a proton into a neutron for some minutes. read more

In positron emission, also called positive beta decay ([math]β^+[/math]-decay), a proton in the parent nucleus decays into a neutron that remains in the daughter nucleus, and the nucleus emits a neutrino and a positron, which is a positive particle like an ordinary electron in mass but of opposite charge. read more

Protons and neutrons are tightly bound to the nucleus. The amount of energy required to remove one is far greater than the energy typically found in chemical reactions. read more