James Chadwick: Biography & Atomic Theory

Instructor: Heather Pier

Heather has taught high school and college science courses, and has a master's degree in geography-climatology.

Learn about English physicist James Chadwick, who discovered the neutron and whose research helped launch the atomic weapons race and the Manhattan Project.

Early Life

Before beginning his illustrious scientific career, James Chadwick came from very humble beginnings. He was born the son of a cotton spinner and a house maid in Bollington, England in 1891. He was an excellent student and had offers to attend prestigious private schools in the area, however his parents (and grandparents, who were his primary caretakers) could not afford the tuition. Fortunately, by the time his college years arrived, Chadwick was able to pass several scholarship exams that helped afford him the opportunity to attend Victoria University of Manchester. His family did not have the money for him to live in university's housing, so he instead walked several miles to school and back each day. In classic absent-minded-scientist form, he discovered physics purely by mistake - as he registered for physics coursework accidentally on the assumption they were math courses. At the time Chadwick was a student, the famous atomic physicist Ernest Rutherford was a faculty member at Victoria, and Rutherford saw much potential in him. Prior to graduation, Chadwick and Rutherford co-authored a study on radioactive energy, which eventually led to the ability to measure gamma radiation.

James Chadwick, during his years in Los Alamos working on the Manhattan Project.

Graduate School and World War I

Chadwick continued his radiation research as a graduate student, this time looking into the absorption of gamma radiation by various materials. He was again able to continue his graduate education through his scholarship-winning efforts, this time receiving the opportunity to study in Berlin under Hans Geiger (and occasionally Albert Einstein), who was one of the world's foremost experts on radiation at the time. It was during his time with Geiger that World War I began, and being that Chadwick was English, he was placed in an internment camp. He was miraculously able to conduct some scientific research there, primarily on the ionization of phosphorus, which he was able to extract from toothpaste. At the end of the war, he was released and returned to the England to again work with Rutherford, this time at his new Cavendish Laboratory at the University of Cambridge. It was during this time at Cambridge that Chadwick earned his Ph.D. for his work on atomic number calculations and nuclear forces. Upon graduation, he officially became Rutherford's research assistant. During his time at Cavendish, he married Aileen Stewart-Brown, with whom he would have two daughters.

Neutrons and the Nobel Prize

As part of his radiation and atomic number research, Chadwick frequently analyzed the structure and composition of the nucleus. Much of his research led to clear cut results; however the newly discovered concept of electron spin clouded things considerably. Chadwick began to notice that there were many elements where the nucleus appeared to contain the proper number of protons and electrons (and thereby the proper mass and charge), but its overall spin was not consistent with the Zeeman effect's predictions. After much experimentation using the newest Geiger counter and Polonium samples, Chadwick was eventually able to conclude that there was a new type of nuclear particle, one which had a detectable mass but no charge, that would help to account for the differences in electron spin and rectify the earlier Zeeman effect-related anomalies. Frederic and Irene Curie were conducting research at the same time on gamma radiation, and during their experiments had unintentionally discovered a particle that seemed to have properties similar to Chadwick's proposed neutral particle. Chadwick took the Curies research and became obsessed with trying to isolate the neutral particle. After only about four months of experimentation, he published his findings that conclusively proved the existence of a neutral particle, the neutron. His work not only changed our interpretation of the nucleus as a whole, but it also helped to rectify numerous issues that other scientists had been having with errors in predicted electron spins. Later research by Chadwick determined the neutron, and in doing so proved that the neutron is an independent particle and not a proton-electron pair because the mass of an individual neutron was not equal to the mass of a proton plus the mass of a neutron. He would receive the 1935 Nobel Prize for his work neutron-related discoveries, as well as the Hughes Medal, the Copley Medal, and the Franklin Medal.

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