Can strong nuclear force exist only between protons and neutrons or anything close together?
To answer your question I must tell you about protons and neutrons. They are not elementary particles, meaning they are composed of even smaller particles. These smaller particles are called ‘‘quarks’’. A proton and a neutron each contain 3 quarks. Now, like the electron has a property called electric charge which lets it interact with the electric field, these quarks have a property called ‘‘color’’ which makes them interact with the strong force. So protons and neutrons actually interact with the strong force because they contain quarks which have ‘‘color’’. Any other particle composed of quarks (or quarks themselves) do interact with the strong force. The group of particles that are composed of quarks, and therefore interact with the strong force, are called ‘‘hadrons’’. An example of those hadrons are particles called Mesons. The next part of your question is about charged particles. If charged particles are hadrons then they are composed of quarks (quarks are electrically charged)
