The model proposed by James Chadwick focuses on the modeling of the atomic nucleus constituted not only by protons (positive charges), but also by neutrons (neutral charges).
From his discovery of the neutron in 1932 (for which he received the Nobel Prize in 1935), Chadwick conceived that the model initially considered that the neutron was an arrangement made up of a proton and an electron, which generated the neutral charge. Later, the German physicist Werner Heisenberg showed that the neutron was a unique and elementary particle.
Chadwick conceived that the atom was understood as a nucleus with protons and neutrons, assuming almost the entire mass of the atom, with the electrons orbiting the nucleus in their corresponding energy levels.
The discovery of the neutron and its atomic model revolutionized the traditional vision of science, given the collisions of neutrons with atomic nuclei and the expulsion of protons out of the atom.
Beta decay is a process through which beta particles (electron or positron) are emitted from the nucleus of the atom, to balance the presence of protons and neutrons in the atomic nucleus.
Due to this process, countless experiments were carried out worldwide, motivated by Chadwick's discovery, to induce the conversion of some neutrons into protons.
Because each chemical element is identified according to the number of protons it has, since Chadwick, the doors have been opened for the creation and/or discovery of new elements.
Later, James emphasized the use of neutrons for the separation of atoms from heavy nuclei into several reduced nuclei through the process of nuclear fission.