The Discovery That Started It All

Lise Meitner

In this blog in the From Berkeley to Berlin series, we’re going to look back in time to figure out how we got into and out of the Berlin Crisis. That Kennedy could face down a thug like Khrushchev wasn’t a given—it didn’t just happen. Like almost everything in life, it took a lot of preparation so that Kennedy would have the needed wherewithall to stand up to a war ultimatum. That preponderant strength that National Security Advisor McGeorge Bundy said was so important in seeing us through a nuclear crisis was created over the course of two decades. The essence of the story in From Berkeley to Berlin is to relate how we as a country developed that preponderant strength, and the story begins a quarter century before the Berlin Crisis.
The hero of this story is going to be, beyond a doubt, Ernest O. Lawrence. Nevertheless, I thought it would be appropriate to highlight this blog with a portrait of Lise Meitner, a world-class physicist who is not a well-known household personality like Albert Einstein or Marie Curie, but she ought to be. That she could decipher a complicated chemistry experiment and come up with a theory for nuclear fission in a matter of days is astounding. The paper she wrote with her nephew launched us into the nuclear age—didn’t know that, did you? Likewise, one of the finest American physicists of the twentieth century, John Wheeler, is introduced through this excerpt taken from my upcoming book.
Like many of you, I’ve read histories of the World War II era about the atomic bomb, and rightfully, many documentaries center the atomic bomb around activities at a remote laboratory called Los Alamos. But are you aware that the discoveries that made an atomic bomb possible occurred in Berkeley? I can only wish I had the time and you had the patience for me to explain why and how those discoveries took place, but perhaps at a later time. Meanwhile, please enjoy these highlights from my upcoming book, From Berkeley to Berlin.

The story of how the United States got out of a nuclear crisis unscathed in 1961 begins with the creation of a scientific laboratory devoted to the study of nuclear physics. Robert G. Sproul became president of the University of California, and he was intent to take the university from being a scientific backwater and turn it into a world-class center of scientific innovation. To accomplish that he promoted an associate professor of physics, Ernest O. Lawrence, a native of South Dakota and the grandson of Norwegian immigrants, to full professorship. Lawrence was an up-and-coming physicist the university had recently recruited to the Berkeley campus, and Sproul thought Lawrence’s passion and zeal to accomplish things would do the trick. Sproul would not be disappointed.
True to expectations, Lawrence sought to do something new and exciting. He invented a machine that accelerated subatomic particles to penetrate the atomic nucleus. He called his invention a magnetic resonance accelerator­, but it became known as the cyclotron. Newspaper journalists called his creation the “atom smasher.”
In August 1931, Sproul gave Lawrence a disused civil engineering building to house a new 27-inch cyclotron. Lawrence called his new home the Penetrating Radiation Laboratory, but within a year, it became the University of California Radiation Laboratory (UCRL)—most called it the Rad Lab. As will soon become evident, UCRL would become the hub around which some of the principal characters and events of this history of the Cold War will revolve. Lawrence’s cyclotron attracted the top experimental physics students in the country as they flocked to join the Rad Lab and become Lawrence’s “cyclotroneers.”
Two early recruits to the Rad Lab played significant roles in the events of this history, and like Lawrence himself, they would become Nobel laureates. One was Edwin McMillan, slight of build, freckled and sandy-haired; raised in Pasadena, California, he earned Bachelor of Science and Master of Science degrees by the age of 22 at the California Institute of Technology (Caltech). In 1932, he received a doctorate in physics while at Princeton and, within two years, he joined the Rad Lab.
The other was Luis Alvarez, a tall and ruddy man with a crop of blond hair. His Celtic looks belied his Hispanic surname, which came from a Cuban émigré grandfather, and a father who was a renowned researcher at the Mayo Clinic; his fair complexion came from his mother, Harriet Smyth, the daughter of Irish missionaries to China. In 1936, Alvarez had a doctorate in physics and Lawrence offered him a position at the Rad Lab.
At about the time Lawrence moved to Berkeley, the University hired a theoretical physicist named J. Robert Oppenheimer. Tall and gangly, Oppenheimer had a narrow face with piercing blue eyes. Oppenheimer and Lawrence complemented each other well. Oppenheimer became the theorist for Lawrence’s Rad Lab: he assembled a group of theoretical physicists who provided theories that explained what the cyclotroneers were discovering. These two friends had so many different characteristics: Lawrence, the rural Lutheran South Dakotan, and Oppenheimer, the urban Jewish New Yorker.
* * *
Young professionals who choose to make physics their lifelong careers have two general paths they can follow: they can become experimental or theoretical physicists. In a nutshell, experimentalists discover new physical phenomena, and theorists explain them. Lawrence happened to be one of the world’s greatest experimentalists. He had two particular attributes that made him extraordinary: he had a remarkable ability to make even the most difficult experiments work, and he was a natural leader who could instill the highest degrees of trust and loyalty in his subordinates. When the world was faced with the dual threats of Nazism and Communism, Lawrence focused his natural traits to find a way to protect America. What spurred him on was a dramatic new discovery in nuclear physics.  
Events began to unfold in December 1938, when nuclear fission was discovered in a chemistry laboratory in Berlin, the capital of Nazi Germany. The discovery came about after the Italian physicist and Nobel laureate Enrico Fermi noticed unusual activity when he struck a thin foil of uranium with neutrons. Fermi had been striking, in turn, all the elements of the periodic table with neutrons. After bombarding each element, he observed a new radioactive element, which is called a radioisotope. When he reached uranium, he observed a substantial increase in radioactivity that he had not seen with any other element. He reported his observations in the Italian physics journal, Ricerca Scientifica,[iii] and that induced the renowned German chemist Otto Hahn to repeat Fermi’s experiment in his laboratory in Berlin, although this time by chemically analyzing the uranium foil after the neutron bombardment.
Hahn found radioisotopes of the element barium in his foil of uranium, which was perplexing—barium is not even close to uranium in the periodic table. He was an excellent chemist, but he needed a good theoretical physicist to interpret his discovery, so he wrote a letter describing what he had seen to his former partner, the Austrian physicist Lise Meitner. 
Meitner was a prominent physicist: she and Hahn together had been awarded the prestigious Leibniz Prize for discovering new elements. But she was Jewish, and when Hitler’s Nazi Party came to power, she was forced to wear a yellow badge in public and was subjected to physical assaults. Hahn helped expedite Meitner’s flight out of Germany, giving her a diamond ring for use in case of emergency; it had belonged to his mother. Meitner settled down in the village of Kungalv, near the city of Göteborg, Sweden.
Amazingly, within days after receiving Hahn’s letter, Meitner and her nephew, Otto Frisch, concluded Hahn had observed uranium nuclei split apart—as a parallel to cells splitting in biology, Frisch called it nuclear fission. Then aunt and nephew co-wrote an article in the scientific journal Nature[iv] that said, among other things, a nuclear fission reaction was a million times more energetic than a chemically explosive reaction. They also said a nuclear fission event released neutrons, so nuclear fissions could theoretically go on indefinitely in a chain reaction, provided enough fissionable atoms were assembled to form a critical mass. Nuclear physicists, including Lawrence, recognized the danger: the discovery of nuclear fission could lead to Adolph Hitler possessing an atomic bomb.
To a nuclear physicist, the article written by Meitner and Frisch raised questions. The great amount of energy released by nuclear fissions should have created a lot of heat, so much so one could have expected the uranium foil to melt, or even disintegrate—but it didn’t. Apparently, the majority of the uranium nuclei in the foil didn’t fission. Why were there so few nuclear fissions?  The answer would come from a Dane and an American. 
A short time after Meitner and Frisch wrote their article in Nature, Nobel laureate Niels Bohr met physicist John Wheeler in New York. They took up quarters in Princeton University, where together, they wrote a scientific article that appeared in the September 1939 issue of Physical Review entitled, “The Mechanism of Nuclear Fission.”[v] In their article, Wheeler and Bohr concluded the nuclear fissions observed in Berlin had not been due to uranium atoms in general; rather, they were due to one isotope of uranium, uranium-235, which comprised less than one percent of the atoms in natural uranium.* Their article appeared the same day Hitler’s Wehrmacht invaded Poland from the west, and Stalin’s Red Army attacked from the east; the Axis partners crushed the country within 30 days and started World War II.
The Wheeler-Bohr article was profound—it opened the door to understanding how to use this newly discovered form of energy. It implied in order to make an atomic bomb, one had to separate the isotope uranium-235 from natural uranium and mold enough of it together to form a critical mass. That presented a challenge: how does one separate one isotope of uranium from other uranium isotopes when all the isotopes react the same way chemically? Lawrence thought he knew how to do that.

[iii] “Professor Enrico Fermi, Academician, Uses Neutrons Formed by Decomposition of Beryllium Under the Action of Alpha Particles of Radium,” New York Times, June 5, 1934, p. 25. This article reports on Fermi’s experiments originally recorded in the Italian science journal, Ricerca Scientifica, in May 1934.
[iv] Lise Meitner and O.R. Frisch, “Disintegration of Uranium by Neutrons: a new type of Nuclear Reaction,” Nature, Volume 143, Issue 3615, February 1939, pp. 239-240.
[v] John Wheeler and Niels Bohr, “The Mechanism of Nuclear Fission,” Physical Review, Vol 56, September 1, 1939.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s