James Chadwick who discovered in 1932 a neutral particle that decayed in a proton and an electron he was assessing together with Niels Bohr a model for this complex. They failed to find a different complex than a point-like electron attracted by a proton of opposite electric charge and so orbiting around it, that was the accepted Bohr’s model for hydrogen. Unfortunately the scientific community had rejected the A.L.Parson’s model proposed (in 1915) for the electron as Toroidal Ring based on Lord Kelvin’ vortex ring for the structure of mater in 1867. Such a model could support the missed opportunity for a correct neutron model (a proton in the center of an electron ring) and for an “electric charge” as the result of the vortices around the ring and not wrongly assumed as an innate property.
The scientific community decided in 1935 arbitrarily that the unstable neutron is similar with the stable proton, with zero charge and that becomes stable inside nuclei. This decision solved the difference between the mass number A and atomic number Z (A≥2Z). Later on the quarks were invented with electric charges +2/3 and –1/3 in order to explain the zero charge of neutrons and their change in the nuclei to protons and vice versa in order to explain the unstable isotopes and other experimental conflicts.
A model based on proton and electron as vortex rings supports a neutron as an unstable complex of a proton-ring of radius 10^-15 m, in the center of an extremely thin electron ring of radius 10^-10 m. Therefore nucleus is a symmetric spinning lattice of proton rings.
My model (see in my profile in Quora) is based on the hypothesis that proton and electron are kinetic energy excitations in the form of cyclonic structures similar to vortex rings inside a pressure field of Ideal Gas (as defined in Boltzmann’s (1866) classical Kinetic Theory of mass-points interacting by perfect elastic collisions).
A macroscopic example of a real pressure field is the pressure field in our Atmosphere where kinetic energy excitations of air molecules are generated in the form of cyclones with the maximum kinetic energy at the walls of their cyclonic eyes.
The Universal Dark Energy (UDE) that fulfills our 3D space and generates the accelerated expansion of our Universe, supports the hypothesis that the UDE is the kinetic energy of the mass-points of a Universal Ideal Gas (UIG) that fulfills our 3D space.
In the pressure field of the UIG many unstable cyclonic forms can be formed but only two sizes of kinetic energy- excitations in the form of vortex rings (and their anti-vortex rings) can be stable. Therefore proton and electron (and their antiparticles) are the only stable ring-shaped cyclones (with a ring-shaped cyclonic eye and an axial cyclonic eye) inside the UIG.
Electron is a ring of radius 10^-10 m with an extremely thin ring-shaped cyclonic eye and proton is of radius 10^-15 m with a thick ring-shaped cyclonic eye and a thick axial cyclonic eye (see the image here below).
The cyclonic swirls around the cyclonic eyes of electron and proton generate (according to Bernoulli principle) strong pressure gradients resulting into the Coulomb force for electron and proton and the Nuclear force for proton. And the weak diffusion flow of mass-points towards the vacuum of the cyclonic eyes generates (according to Bernoulli principle) a weak pressure gradient resulting into the Gravity force.
Neutron being a complex of a proton in the center of an electron ring cannot fit inside nuclei. A stable nucleus (with mass number A) is a symmetric spinning lattice of proton rings. A number N of cyclonic swirls of the rings that are placed with diverse orientations are negated and so the nucleus attracts only Z=A-N electron rings that are knitting a cage.
For example the 3D image of He-4 atom is shown here below. It is not 4 spherical nucleons (2protons and 2 neutrons) with quarks and gluons inside.
For example the 3D image of the outer electron rings of Ne atom is shown here below as a knitted cage (8 electron rings inscribed in the faces of two successive 4-hedra). It is not 8 orbital clouds of point-like electrons.
Nuclei with proton rings unstably oriented are unstable isotopes. Reorientation of unstable isotopes changes the Z resulting into the contraction of the electronic cage and the ejection of its outermost electron or into expansion of the electronic cage and ejection of its outermost electron that is inverted to positron, Electron capture occurs more often for heavy elements because their thick electronic cage holds its outermost electron ring as it is not sufficiently expanded by the reorientation of a proton ring.