James Chadwick (1891 - 1974)

Was Rutherford's student who builded off of Rutherfords ideas.

Took atoms of Beryllium, Boron, and Lithium, then shot alpha particle at them. (This is similar to how Rutherford shot alpha particles at the gold foil). Chadwick notices that rays get released from the Beryllium, Boron, and Lithium atoms. He realizes that whatever is getting released doesn't have a charge. Chadwick know that the particles being realeased can't be protons because they are positively charged. It can't be electrons because they are negatively charged. Chadwick put wax in front of the rays that are shooting out of the atoms. As a result, protons quickly come shooting out of the wax. Chadwick knows that whatever is coming out of the wax has to have the same mass of the protons.

Chadwick concludes that the particles that are being shot out of the atom has no charge and has to be about the same size and mass of a proton. These uncharged particles are called nuetrons. 

He claimed neutrons were importatnt since they held the positively charged protons together.