Only the two-particle systems (P,e), (p,e), (p,E) and (P,E) can build bound states; all other two-particle systems cannot build bound states.
The two-particle systems (e,p) and (P,E) have the gravitational masses zero, mg =0. If the inertial masses, mi, are also zero these states are to be called as neutrinos. The sizes of the neutrinos are 0.703∙10^-13 cm, respectively 0.383 ∙10^-16 cm.
The (P,e)-system can build the hydrogen atom at the bound energy of 13.8 eV, the stable neutron N0 at 2.04 MeV bound energy with the size of 0.702∙10^-13 cm. If the bound energy of the (P,e)-system is E(bound) = (mP + me) ∙c^2, the inertial mass is zero and this state has the size of 0.382 ∙10^-16 cm.
The approach of two particles in the bound states cannot be less than 0.382 ∙10^-16 cm; the stable elementary particles do not annihilate.
The energy-mass equivalent relation of Einstein, E = m∙c^2 is generally not valid; a particle system with the mass m can only radiate the energy E = m∙c^2 if before the radiation the bound energy was E = m∙c^2. But also in this state the elementary particles, e, p, P and E, are present.