The Nobel Prize in Physics 1980
James Cronin, Val Fitch
I was born the youngest of three
children, on a cattle ranch in Cherry County, Nebraska, not far
from the South Dakota border, on March 10, 1923. This is a very
sparsely populated part of the United States and remote from any
center of population. It seems incredible by modern standards
that by the age of 20 my father, Fred Fitch, had acquired a ranch
of more than 4 square miles and had persuaded a local school
teacher, Frances Logsdon, to marry and join him in living there.
They moved to the ranch just 20 years after the battle of Wounded
Knee, which occurred about 40 miles northwest. I mention this
because our living close to their reservation made the Sioux
Indians very much a part of our environment. My father, while not
fluent, spoke their language. They recognized his friendly
interest on their behalf by making him an honorary chief.
Not long after my birth my father was badly injured when a horse he was riding fell with him. He subsequently had to give up the physically strenuous activity associated with running a ranch and raising cattle. The family moved to Gordon, Nebraska, a town about 25 miles away, where my father entered the insurance business. All of my formal schooling through high school was in the public schools of Gordon. During this period my parents retained ownership of the ranch but the operation was largely left to others. E.B. White has defined farming as 10% agriculture and 90% fixing something that has gotten broken. My memories of ranching are primarily not the romantic ones of rounding up and branding cattle but rather of oiling windmills and fixing fences.
Probably the most significant occurrence in my education came when, as a soldier in the U.S. Army in WWII, I was sent to Los Alamos, New Mexico, to work on the Manhattan Project. The work I did there under the direction of Ernest Titterton, a member of the British Mission, was highly stimulating. The laboratory was small and even as a technician garbed in a military fatigue uniform I had the opportunity to meet and see at work many of the great figures in physics: Fermi, Bohr, Chadwick, Rabi, Tolman. I have recorded some of the experiences from those days in a chapter in All in Our Time, a book edited by Jane Wilson and published by the Bulletin of Atomic Scientists. I spent 3 years at Los Alamos and in that period learned well the techniques of experimental physics. I observed that the most accomplished experimentalists were also the ones who knew most about electronics and electronic techniques were the first I learned. But mainly I learned, in approaching the measurement of new phenomena, not just to consider using existing apparatus but to allow the mind to wander freely and invent new ways of doing the job.
Robert Bacher, the leader of the physics division in which I worked, offered me a graduate assistantship at Cornell after the war but I still had to finish the work for an undergraduate degree. This I did at McGill University. And then another opportunity for graduate work came from Columbia and I ended up there working with Jim Rainwater for my Ph.D. thesis. One day in his of fice, which he shared at the time with Aage Bohr, he handed me a preprint of a paper by John Wheeler devoted to µ-mesic atoms. This paper emphasized, in the case of the heavier nuclei, the extreme sensitivity of the Is level to the size of the nucleus. Even though the radiation from these atoms had never been observed, these atomic systems might be a good thesis topic. At this same time a convergence of technical developments took place. The Columbia Nevis cyclotron was just coming into operation. The beams of (pi)-measons from the cyclotron contained an admixture of µ-measons which came frome the decay of the (pi)'s and which could be separated by range. Sodium iodide with thallium activation had just been shown by Hofstadter to be an excellent scintillation counter and energy spectrometer for gamma rays. And there were new phototubes just being produced by RCA which were suitable matches to sodium iodide crystals to convert the scintillations to electrical signals. The other essential ingredient to make a gamma-ray spectrometer was a multichannel pulse height analyzer which, utilizing my Los Alamos experience, I designed and built with the aid of a technician. The net result of all the effort for my thesis was the pioneering work on µ-mesic atoms. It is of interest to note that we came very close to missing the observation of the gamma-rays completely. Wheeler had calculated the 2p-1s transition energy in Pb, using the then accepted nuclear radius 1.4 A1/3 fermi, to be around 4.5 MeV. Correspondingly, we had set our spectrometer to look in that energy region. After several frustrating days, Rainwater suggested we broaden the range and then the peak appeared - not at 4.5 MeV but at 6 MeV! The nucleus was substantially smaller than had been deduced from other effects. Shortly afterwards Hofstadter got the same results from his electron scattering experiments. While the µ-mesic atom measurements give the rms radius of the nucleus with extreme accuracy the electron scattering results have the advantage of yielding many moments to the charge distribution. Now the best information is obtained by combining the results from both µ-mesic atoms and electron scattering.
Subsequently, in making precise gamma-ray measurements to obtain a better mass value for the µ-meson, we found that substantial corrections for the vacuum polarization were required to get agreement with independent mass determinations. While the vacuum polarization is about 2% of the Lamb shift in hydrogen it is the very dominant electrodynamic correction in µ-mesic atoms.
My interest then shifted to the strange particles and K mesons but I had learned from my work at Columbia the delights of unexpected results and the challenge they present in understanding nature. I took a position at Princeton where, most often working with a few graduate students, I spent the next 20 years studying K-mesons. The ultimate in unexpected results was that which was recognized by the Nobel Foundation in 1980, the discovery of CP-violation.
At any one time there is a natural tendency among physicists to believe that we already know the essential ingredients of a comprehensive theory. But each time a new frontier of observation is broached we inevitably discover new phenomena which force us to modify substantially our previous conceptions. I believe this process to be unending, that the delights and challenges of unexpected discovery will continue always.
It is highly improbable, a priori, to begin life on a cattle ranch and then appear in Stockholm to receive the Nobel Prize in physics. But it is much less improbable to me when I reflect on the good fortune I have had in the ambiance provided by my parents, my family, my teachers, colleagues and students. I have two sons from my marriage to Elise Cunningham who died in 1972. In 1976 I married Daisy Harper who brought with her three stepchildren into my life.
Honors and Distinctions
I am a fellow of the American Physical Society and the American Association for the Advancement of Science, a member of the American Academy of Arts and Sciences and the National Academy of Sciences. I hold the Cyrus Fogg Brackett Professorship of Physics at Princeton University and since 1976 have served as chairman of the Physics Department. I received the E. O. Lawrence award in 1968. In 1967 Jim Cronin and I received the Research Corporation award for our work on CP violation and in 1976 the John Price Witherill medal of the Franklin Institute.
From Les Prix Nobel. The Nobel Prizes 1980, Editor Wilhelm Odelberg, [Nobel Foundation], Stockholm, 1981
This autobiography/biography was written at the time of the award and later published in the book series Les Prix Nobel/Nobel Lectures. The information is sometimes updated with an addendum submitted by the Laureate.
Copyright © The Nobel Foundation 1980