James Chadwick

James Chadwick

1. Who Was He ?

   • Sir James Chadwick, CH, FRS, was an English physicist who was given the 1935 Nobel Prize in physics for his discovery of the neutron in the year 1932.
   • He was the head of the British team that worked on the Manhattan Project during the Second World War. He was knighted in England in 1945 for achievements in physics.

2. What Did They Find?

   • James Chadwick found the third elementary particle of the atom; the neutron.
   • Chadwick used the idea from Rutherford that there was another particle in atoms to commence his research, he tried and tried and tried to prove the theory correct an succeded

3. What Was Their Experiment?

   • Gamma rays eject electrons from metals; they thought the same thing was happening to the protons in the paraffin. The beryllium rays were not gamma rays because the rays coming from the beryllium had far more energy. Chadwick recognized the beryllium rays as neutrons. Because of neutrons are neutral, they can penetrate thick layers of different materials because there movement is not disturbed by the positively or negatively charged particles in the penetrated material. Chadwick carried out his own experiments and confirmed that he had finally found the neutron.

4. What Did They Find?

   • Chadwick bombarded boron with alpha particles which emitted neutral rays, like beryllium, and placed a hydrogen target in the path of the rays. When the rays hit the hydrogen target, protons flew out. He measured the velocity of the protons. Using the laws of conservation of momentum energy he was able to calculate the mass of the neutral particle. From the velocity of the protons flying out, he could calculate the mass of the projectile, in this case, the mass of the neutrons. The mass of the neutral particle is 1.0067.