Chadwick repeated their experiments but with the goal of looking for a neutral particle --
one with the same mass as a proton, but with zero charge. His experiments were successful. He was able to
determine that the neutron did exist and that its mass was about 0.1 percent more than the proton's. He
published his findings with characteristic modesty in a first paper entitled "Possible Existence of Neutron." In
1935 he received the Nobel Prize for his discovery.