James Chadwick

By: Sydney Kummer, Caroline Bock, & Lauren Frezza

Background History

James Chadwick was born in Manchester, United Kingdom on October 20, 1891. Chadwick Senior, his father, owned a laundry business in Manchester. When he was accepted full scholarship to the University of Manchester, he was mistakenly admitted under physics when he intended to study mathematics. Being too shy to clear up the mistake, Chadwick stayed in physics which sparked his monumental career. Throughout his years at the University of Manchester he created strong friendships with other chemists such as Ernest Rutherford, Niels Bohr, and Hans Gieger.

Experimental Design

Chadwick carried out a series of experiments to determine the development of the neuron. Overall, he discovered that the neuron is elusive, which means it is difficult to find, catch, or receive. In February of 1932 James Chadwick finally discovered the neutron after three weeks of around the clock research. His research was influenced by the successes and mishaps of other scientists. Chadwick used a vacuum chamber filled with polonium and a piece of beryllium.
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A Lifetime of Accomplishments

  1. While Chadwick was in Germany with his friend from college Geiger, World War l broke out. He was held captive for four years in a horse stable, cold and hungry. Although he was trapped in horrible conditions be decided to try to carry out scientific experiments. He convinced his German captors to give him a bunsen burner, which he used to the best of his ability despite it missing a bellows. Although none of his experiments turned out quite right, it kept his spirits up during this dark time.
  2. James Chadwick was also a member of the Maud Committee, which was created during the race to make the first bomb. His duties on the committee were primarily organization, but throughout time he became more of a spokesperson. Because of his knowledge, he convinced British government and military leaders to move ahead with the project, where he continued to influence the exploration of the bomb.
  3. In 1935, Chadwick received the Nobel Prize in physics.
  4. In 1945 James Chadwick was knighted by King George Vl for his accomplishments to the scientific community. From then on he was known as Sir James Chadwick.
James Chadwick Cartoon: Discovery of the Neutron
James Chadwick and the neutron

The Data and Experiment

In order for Chadwick to discover the neutron, he had to run an experiment to test out his hypothesis. He thought the energy being created along the neutral radiation were neutrons. Chadwick conducted an experiment using a vacuum chamber filled with polonium and a piece of beryllium. When the alpha rays from the polonium hit the piece of beryllium, it created mysterious neutral rays. He then put a target int he path of the rays which caused atoms to knock out of it. The now electrically charged atoms flew into a chamber filled with gas that ionized the gas molecules. The molecules drifted towards an electrode which he then measured the current flowing through it.

Chadwick then tested it again using different elements as targets and measured the energy needed to eject the atoms. Nothing could explain the speed of the atoms.
He had to measure the mass of the collision to prove his hypothesis. He used the laws of conservation of momentum and energy to calculate the mass which ended up to be 1.0067 times the mass of the proton. Chadwick proved his hypothesis that the neutral radiation was a neutron.

Chadwick's Discovery and Atomic Model

James Chadwick discovered the third particle to an atom; the neutron. With protons (positive charge) and electrons (negative charge) already discovered, Chadwick believed there was another type of particle with no charge due to his observation of the atomic mass quantity always being larger than the atomic number of an atom. He knew that electrons had almost no mass, and that the protons of an atom couldn't be the only mass adding to create the total atomic mass. Therefore, he concluded that there must be a particle with no charge (doesn't "show up" in the atomic number of an atom) but adds mass to the atom ("shows up" in the atomic mass of the atom). He theory was a success and declared valid.

With his new discovery of the neutron, Chadwick was able to develop his improved version of the atom, as shown below:

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