SOMETIMES YOU run across a photo that jumps off the page. I saw a photo like that in January 2024, during the run-up to the film industry’s Academy Awards.

At the time, there had been much conversation and analysis of Christopher Nolan’s dramatic opus Oppenheimer—a film the Associated Press called “a complex, fission-filled drama.” (The film would win seven Oscars in early 2024.)

The movie was on my mind when I came across a 1939 group photo from the Radiation Laboratory of the University of California at Berkeley. In it, a number of physicists pose on the 220-ton magnet yoke of a 60-inch-diameter cyclotron. The device would ultimately play a key role in developing the world’s nuclear age, particularly through the Manhattan Project: the top-secret WWII allied effort to develop nuclear weapons before the German military regime could.

What’s less widely known is how many scientific roads related to that research touch the University of Minnesota—and how alumni and faculty here played parts in the process. In fact, several individuals memorialized on the famed U of M Scholar’s Walk had significant roles in research related to the events depicted in Oppenheimer.

For example, J. Robert Oppenheimer’s younger brother, physicist Frank Oppenheimer, joined his brother on the pivotal Manhattan Project from 1941 to 1945, and would later become an associate professor of physics at the U of M from 1947 to 1949.

But that’s only the tip of the iceberg.

How it started

Front and center in the “who’s who of nuclear science photo” is experimental physicist Ernest Orlando Lawrence, who earned his master’s degree from the U of M in 1922. (EOL, as Lawrence was known to his colleagues, was played in the film by actor and St. Paul native Josh Hartnett.)

In the center rear of the photo stands an almost boyish J. Robert Oppenheimer, subject of the film, and head of the theoretical physics group at Berkeley.

For those who haven’t seen it, Oppenheimer is the story of a brilliant but complicated man, focusing on the scientific effort he led in the New Mexico desert to develop and test the world’s first nuclear weapon. It covers the period from his work as a fledgling graduate student at Cambridge in the 1920s to his role as a key figure in ending the brutal war in the Pacific, although at an unfathomable cost of civilian life.

(Those actions continue to resonate today: In 2024, the Nobel Peace Prize was awarded to Nihon Hidankyo, a Japanese group dedicated to achieving “a world free of nuclear weapons and for demonstrating through witness testimony that nuclear weapons must never be used again,” according to the Nobel Committee.)

The movie ends with Congressional security hearings in the 1950s and Oppenheimer’s exile from an official role in charting the course of nuclear policy within the U.S government. He and his brother Frank, along with many others, were caught up in a postwar frenzy designed to root out anyone deemed to have shown communist sympathies in the past.

A wartime race

Nuclear fission—the splitting of a nucleus with an accompanying release of a tremendous amount of energy—was demonstrated in uranium by German physicists in December 1938.

As described in Richard Rhodes’ Pulitzer Prize-winning The Making of the Atomic Bomb, the scientific community worldwide recognized the military potential of the reaction immediately, initiating a cascade of experimentation and security measures in the U.S.

Hungarian physicist Leo Szilard was one who realized those nuclear chain reactions could be used to create atomic weapons. In August 1939, he wrote a letter to Albert Einstein to give to President Franklin D. Roosevelt warning that as a result, an “extremely powerful bomb” might be constructed. (Einstein would later express regret at the part he played in forwarding the letter and thereby accelerating the nuclear arms race.)

Fearing ongoing research and development by Nazi Germany, Roosevelt formed an Advisory Committee on Uranium, chaired by the highest-ranking physical scientist in the federal government, Lyman Briggs, head of the National Bureau of Standards (NBS). The committee, composed of representatives of the Army and Navy and leading physicists from throughout academia, met for the first time on October 21, 1939. Its purpose was to assess the feasibility of an atomic bomb—and then ramp up efforts to a production stage.

That process was overseen by several scientists with U of M connections who were added to the reorganized committee, including Merle Tuve, Gregory Breit (more about them below), and Edward Condon, who taught briefly at Minnesota in the 1930s and eventually went on to succeed Briggs as director at NBS in 1945.

At roughly the same time, Lawrence, who was by then working in the Berkeley physics department, won the 1939 Nobel Prize in physics for inventing and developing the cyclotron, a type of atom smasher in which subatomic particles such as protons are targeted on a variety of materials. Using it enables observation of nuclear reactions like the production of new isotopes.

His development would prove pivotal in advancing the nuclear age.

EOL and Merle Tuve

Ernest Orlando Lawrence was born in 1901 and grew up Canton, South Dakota. His shift from a broad interest in science and medicine to a focus on physics was nurtured by University of South Dakota faculty member Lewis E. Akeley, and by Lawrence’s close boyhood friend from Canton, Merle Tuve, who earned his bachelor’s in electrical engineering at the U of M in 1922.

Forged in childhood, the Tuve-Lawrence friendship had an almost storybook quality. In Canton, a town of about 2,000 just south of Sioux Falls, two boys born six weeks apart and living across the street from one another would start experimenting with gliders and radios during their childhood.

Tuve eventually headed to the U of M to pursue electrical engineering. Lawrence would spend a year at St. Olaf College in Northfield, Minnesota, before transferring to the University of South Dakota, where he graduated in 1922. Both men then began graduate studies in physics at the U of M that same year.

At the University, a faculty member and English physicist named William Francis Gray Swann became Lawrence’s thesis advisor. During that time, Swann provided Lawrence with an experimentalist model that guided his prolific body of work for years to come: Swann’s mandate? “Cut-and-try sometimes is more important than too-prolonged theorizing.”

Lawrence earned his master’s from the U of M in 1923 and followed Swann to Yale, earning his doctorate there in 1925. Tuve earned his master’s that same year and went on to a doctorate at Johns Hopkins and a research position at the Carnegie Institution of Washington (CIW).

While at Carnegie, Tuve reconnected with theoretical physicist Gregory Breit, who’d also been part of the faculty at the U of M in 1923-1924. The two men worked together in the Department of Terrestrial Magnetism (DTM) from 1924 to 1929 to develop an atom smasher.

Despite the somewhat anachronistic name, the DTM emerging by the early 1930s was at the cutting edge of nuclear physics. In his role as head of the National Defense Research Committee, the head of CIW, Vannevar Bush, also functioned as the de facto science adviser to President Franklin Delano Roosevelt.

Working behind the scenes, Breit, Tuve, and Bush were key players in directing funds, setting research priorities, and implementing a governing structure that would evolve by wartime in 1942 to become the Manhattan Project under General Leslie Groves, played by Matt Damon in Oppenheimer. (Until that transition, Breit served in the central scientific role that would come to be occupied by J. Robert Oppenheimer.)

A few years prior, in 1928, Lawrence had moved from an assistant professor position at Yale to become an associate professor at Berkeley. Conversations with his friend Tuve, who was already using high voltage devices to accelerate charged particles, had helped change Lawrence’s research at Berkeley to focus on cyclotron development. Two years later, at age 29, Lawrence became the youngest full professor on the faculty.

Nine years later, at his 1939 Nobel Prize ceremony, the head of the Berkeley physics department noted: “By an interesting coincidence, one of Dr. Lawrence’s intimate boyhood friends, Dr. Merle A. Tuve, is at present in charge of nuclear physics research at the Carnegie Institution of Washington, where a huge 60-inch cyclotron, similar to the large Berkeley cyclotron, is under construction.”

During the Nobel presentation enumerating Lawrence’s many accomplishments, the speaker noted that the “first published scientific paper by Dr. Lawrence is dated May 1924.” It was Lawrence’s U of M master’s research.

More U of M connections

Lawrence, Breit, and Tuve weren’t the only U of M figures who played a part in discoveries that led to the mammoth Manhattan Project. Born in St. Paul in 1911, Alfred “Al” Nier (B.E.E. ’31, M.S. ’33, Ph.D. ’36) spent most of his career at the U of M. During 1936-1938, he was on a postdoctoral research fellowship at Harvard, working under Kenneth Bainbridge, who would later become the director of the Trinity Test—the world’s first nuclear explosion. From 1943-1945, Nier was in New York City working for the Manhattan Project.

Nier’s expertise was in mass spectrometry: determining the mass and relative abundance of atoms in an ionized sample. On October 28, 1939, Enrico Fermi, a physicist at Columbia University who’s been called the “architect of the nuclear age” and who was also part of the Manhattan Project, wrote to Nier with an important question:

It took Nier about 10 days to design and construct a new instrument in his U of M lab to find the answer to Fermi’s question. He did his own machining and was supported by a skilled glassblower in the department.

In two 10-hour runs in late February 1940, Nier was able to collect tiny quantities of the separated isotopes on nickel-chromium plates. He put the plates in an envelope with a handwritten letter and mailed them special delivery to Fermi and his colleagues at Columbia from the main Minneapolis post office on the afternoon of February 29.

The envelope and contents arrived safely the following afternoon. The plates were then bombarded with neutrons from the Columbia cyclotron. By that evening, it was clear that fission only occurred in the U-235 fraction, fissionable uranium. That meant a process needed to be developed to increase the content of U-235 relative to the far more abundant U-238 isotope (termed enrichment). The goal was to achieve the critical mass of fissionable U-235 needed to achieve a sustained nuclear chain reaction.

Nier was the senior author on a March 3, 1940, letter to the editor in the Physical Review, the world’s premier physics journal, edited from 1926 to 1950 by the U of M’s John Tate (namesake for Tate Hall). The letter concluded: “These experiments emphasize the importance of uranium isotope separation on a larger scale for the investigation of chain reaction possibilities in uranium.”

The short account of the work would also essentially slam a door on further open publications about nuclear fission. The force behind this voluntary censorship on uranium investigations by American scientists was Gregory Breit, who was afraid of aiding the Germans in their quest for a nuclear weapon.

In 1941, Lawrence visited Nier in Minneapolis. He viewed combining a hybrid mass spectrometer like Nier’s with his cyclotron as a possible path forward for scaling up U-235 production, which would be necessary in atomic weaponry. The result was the calutron, an abbreviation which stood for the California University cyclotron.

This work at Berkeley set the stage for the next step. Construction of the massive Y-12 enrichment plant in Tennessee was approved by an advisory committee that once again included Gregory Breit. Tuve initially served on the committee, but left to develop a proximity fuse for use in anti-aircraft and other artillery shells (it proved to be a game changer for the Allies during WWII).

Groundbreaking took place under high security at Oak Ridge, Tennessee, in February 1943. Lawrence and his team provided guidance on the design, construction, and operation of 1,152 calutrons installed at Y-12. The U-235 separated at Y-12 and a nearby K-25 gaseous diffusion plant would ultimately be used in the bomb dropped on Hiroshima. (The bombs used in the Trinity test and the Nagasaki bomb would use plutonium made at Hanford, Washington, from non-enriched uranium.)

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