Chadwick used the results of his experiment to come up with the theory that the nucleus contained more particles than just protons. He based his theory on two main observations from his experiments:

1. Deflection of alpha particles: When alpha particles were fired at a thin gold foil, some were deflected at large angles, indicating that they had collided with something massive inside the atom. These collisions were consistent with the idea that the atom contained positively charged particles (protons) that were repelling the positively charged alpha particles.

2. Neutrality of atoms: Despite the presence of positively charged protons, atoms as a whole are neutral. This observation suggested that there were also negatively charged particles present within the atom to balance out the positive charge.

To explain these observations, Chadwick proposed that the nucleus contained a third type of particle in addition to protons: the neutron. Neutrons are neutral particles with approximately the same mass as protons, and they help to balance out the positive charge of protons to give atoms their overall neutral charge.

Chadwick's theory of the neutron was confirmed by later experiments, and it led to a better understanding of the structure of the atom and the nucleus.