James Chadwick discovered the neutron in 1932, a neutral subatomic particle with approximately the same mass as a proton but no electric charge

. This discovery was fundamental for nuclear science because neutrons, unlike charged particles, could penetrate and split the nuclei of heavy atoms without being repelled by electrical forces

. Chadwick's work explained the extra mass and spin of atomic nuclei and resolved anomalies in atomic theory related to nuclear structure

. He demonstrated the neutron's existence through experiments involving radiation and paraffin wax, detecting protons ejected by neutral particles, proving these were not gamma rays but neutrons

. For this epoch-making discovery, Chadwick was awarded the Nobel Prize in Physics in 1935

. His discovery paved the way for nuclear fission, which led to the development of the atomic bomb, and he later contributed to the Manhattan Project during World War II