Describe how neutrons were discovered

They respond by emitting radiation when shot with alpha particles

Originally scientists believed in the plum pudding model of the atom (sphere of positive charge surrounded by smaller spheres of negative charge) then Rutherford did his scattering experiment (he shot alpha particles at a piece of gold foil some particles passed straight through the empty space of the atom, some were slightly deflected as they were closer to the atom's nucleus and some were completely reflected because they were headed in the path of the atom's nucleus