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Saturday, April 11, 2020

James Chadwick and the neutron


Photo source: Wikimedia Commons


James Chadwick (1881-1974) was a British physicist best known for discovering the neutron. Physicist Luis Alvarez said,


"In that same year [1932], the number of [known] particles was suddenly doubled. In two beautiful experiments, Chadwick showed that the neutron existed, and Anderson photographed the first unmistakable positron track." (Nobel Lecture, 1968)


Wikipedia says,


"In February 1932, after only about two weeks of experimentation with neutrons, Chadwick sent a letter to Nature titled, 'Possible Existence of a Neutron'... His discovery was a milestone in understanding the nucleus." (Wikipedia: James Chadwick, 6.28.21 UTC 18:11)


The rest of this post is some quotes from Chadwick.


Discovery of the neutron


"The neutron was difficult to catch. Other particles can be seen and their actions watched, but the neutron we could not see and it left no traces of its passage." (Quoted by New York Times, 1932)


"I am afraid neutrons will not be of any use to any one." (From interview, when asked if his discovery had practical importance, New York Times, 1932)


"Much interesting and important work was done, but it was work of consolidation rather than of discovery; in spite of may attempts the paths to new fields could not be found." (




"A radioactive substance may be defined as one which possesses the property of emitting spontaneously radiations capable of passing through sheets of metal and other substances opaque to light." (


"It has been seen that the study of radioactivity has provided direct evidence of the existence of the atom as a unit in the structure of matter." (


"Radioactive changes are quite different from ordinary chemical changes, for they deal with the disruption of the atom while chemical changes deal with the dissociation of molecules into atoms and the modes of combination of the atoms." (


Nuclear weapons


"I remember the spring of 1941 to this day. I realized then that a nuclear bomb was not only possible - it was inevitable... And I had then to start taking sleeping pills. It was the only remedy." (Interview with Charles Weiner, 1969)