184 inch Cyclotron – the basis for the calutron
In this blog, we’re going to learn how Lawrence got himself involved with starting an American atomic program. But first, in my last blog, I spoke a little about Lise Meitner and her role in starting a nuclear age—by unraveling a mysterious chemistry experiment and coming up with a theory for how atoms split apart, nuclear fission. This presents a good time to talk about another world class physicist who is not well known by Americans, John Archibald Wheeler.
John Archibald Wheeler— who coined the phrase “Black Hole”
Wheeler was arguably the greatest American physicist of the twentieth century. When he co-authored a book on general relativity in the 1970s, I can vouch it was a buzz among physics students at MIT and it was an instant best seller. As a newly minted PhD in the 1930s, he spent a year in Copenhagen as a fellow in Nobel laureate Niels Bohr’s Institute for Theoretical Physics. When Wheeler and Bohr wrote their article on nuclear fission a few months after Meitner’s article in Nature, they used physics principles annunciated by Enrico Fermi a short time earlier to figure out it was uranium-235 that was undergoing nuclear fission in the Berlin chemistry experiment.
I remember how curious I was while doing research for this book about how Wheeler and Bohr were able to figure that out so quickly. I am sorely tempted to explain how they did it, but I’m afraid I will lose most if not all of you readers if I did. (Dying of curiosity about how they did it? Email me, or you can read their article that I cited, or read Wheeler’s autobiography, co-written with Ken Ford, who has endorsed my book.)
I am guessing most of you had no idea that Lawrence was principally responsible for creating the MIT Radiation Laboratory, which developed radar technology for America’s military. (Why on earth didn’t they use it before Pearl Harbor?) When you read pertinent excerpts from my book in this blog, you will see that I bring up the radar research because it brought together David Griggs and Johnny Foster with Lawrence. That was important, for it paid dividends years later when Lawrence created a nuclear weapons laboratory in Livermore, California.
Johnny Foster departed Cambridge, Massachusetts aboard a troop ship bound for Italy. Along the way, the ship’s navigational compass broke down and they were sailing alone, separated from the safety of a convoy. The captain summoned Johnny to fix it, which somehow, he did. We will see in a later blog that the twenty-one-year-old Johnny coached American bomber crews to outwit the German radar being used spot and destroy the American bombers. My uncle Tommy, the man I’m named after, was a B24 bombardier in Europe at the time, and he was killed over France. I only wish Johnny’s tactics could have been available to help save his life.
I hope you enjoy this blog, sixth in the series, that highllights one chapter from my upcoming book, From Berkeley to Berlin:
Once he had digested the two articles on nuclear fission, Lawrence, true to his nature, felt he had to do something. Nazi Germany had an ample supply of world-class physicists who understood the implications of the Wheeler-Bohr article—they would know how to make an atomic bomb. Someone had to wake up government officials about a catastrophic threat steamrolling towards the country since Hahn had made that discovery in his chemistry laboratory.
Lawrence approached an engineer named Vannevar Bush, who fulfilled a role that would later be called the President’s scientific advisor. Bush had made his fortune when he and two associates invented a means for a household radio to run off of an electrical outlet rather than a battery. With that invention, he co-founded the American Appliance Company, which became the parent company to Raytheon Corporation. Bush had the ear of the President, and Lawrence pushed him to convince Roosevelt to start an atomic program.
What frustrated Lawrence the most was that Bush wasn’t convinced an atomic bomb could be built. Besides, his mind was wrapped around the problem of how the country should prepare itself to enter a war raging in Europe. Bush looked to technology to win an upcoming war; he had been impressed that it was British technology, especially its radar, that had played a crucial role in England winning the Battle of Britain and staving off a Nazi invasion. The British had developed a means to make radar more effective, and Bush wanted Lawrence, who else, to leverage the British technology to develop radar systems that could affect the war he was sure America was about to enter.
Lawrence volunteered to create the Massachusetts Institute of Technology (MIT) Radiation Laboratory—the style of its name and organization were borrowed from Lawrence’s UCRL in Berkeley. Lawrence recruited scientists from around the nation and sent his chief Rad Lab lieutenants, Edwin McMillan and Luis Alvarez, to help get it started.
After arriving at MIT, Alvarez created a project to develop what came to be known as Ground Controlled Approach Radar (GCAR), that is, radar used to guide airplanes to land safely. To conduct research, the project needed an airplane on which to practice. So, one of Alvarez’ team members, Ivan Getting, who would later introduce the world to the Global Positioning System (GPS), introduced Alvarez to a pilot with a private airplane, David Griggs, who happened to also be a first-class physicist. The GCAR program would later affect America’s nuclear weapons program by bringing Alvarez, Griggs, and Lawrence together—they became lifelong friends.
There was another way the MIT Radiation Laboratory was connected to America’s nuclear program. While recruiting researchers for the laboratory, Lawrence had reached out to a renowned Canadian physicist and personal friend, John Stuart Foster, and asked him to help with the radar research. Foster agreed to join the effort and lend his talent, and he brought his college-age son, Johnny, to accompany him. Once settled in Cambridge, Massachusetts, Foster obtained a position for his son at the Harvard Research Laboratory, where Johnny conducted his own radar research. After a year, Johnny volunteered his services to the Army Air Corps, and he was soon deployed to be a scientific advisor to 15th Army Air Force in Italy. As had happened to David Griggs, Johnny Foster established a strong relationship with Alvarez and Lawrence, and after returning from the Italian theater of war, the younger Foster joined the Rad Lab in Berkeley.
* * *
Once he had the MIT Radiation Laboratory up and running, Lawrence reignited his passion to get an American atomic program started. On a bitterly cold Boston morning on March 17, 1941, Saint Patrick’s Day, he told Bush about a machine he invented, the calutron, that could enrich uranium, that is, it could extract uranium-235 from natural uranium. Regardless, Bush remained stubbornly skeptical that an atomic bomb could be made. That was until he read a report from the British government, the MAUD Report, which caused him to change his mind and commit himself to building an atomic program.
Although irritated with theoretical talks couched with degrees of uncertainty from physicists like Lawrence, Bush the engineer understood the British concept, which was laid out in plain terms. The report said the British government believed it feasible to make an atomic bomb, and it described the way to do it: “We have now reached the conclusion that it will be possible to make an effective uranium bomb which, containing some 25 lbs. of active material [uranium-235], would be equivalent as regards destructive effect of 1,800 tons of T.N.T.”
While Bush deliberated an atomic program, two members of Lawrence’s Rad Lab were making discoveries that would drastically affect nuclear research. Before departing Berkeley to join the MIT Radiation Laboratory, Edwin McMillan had decided to replicate Hahn’s experiment that discovered nuclear fission. After bombarding a foil of uranium with neutrons emitted from a cyclotron, McMillan observed that the neutrons were causing uranium-235 nuclei to fission all right. But McMillan was a thorough physicist, and chemist, and he found other neutrons were being absorbed by nuclei of the majority isotope of uranium, uranium-238, to become a radioisotope, uranium-239. Then McMillan discovered that uranium-239 decayed into a new element, which he called neptunium. When McMillan departed the Rad Lab for Cambridge, Massachusetts, a Rad Lab radiochemist working down the hallway from him, Glenn Seaborg, took over McMillan’s experiments. Seaborg discovered neptunium decayed into yet another new element, which he called plutonium. Their discoveries would earn McMillan and Seaborg the Nobel Prize—they were the first two of six distinguished Rad Lab physicists and chemists who would earn that distinction.
Seaborg and McMillan
On March 28, 1941, one week after Lawrence had met Bush in Boston to promote an atomic program, Seaborg used a Rad Lab cyclotron to expose 5 micrograms of plutonium to neutrons. He found that plutonium readily fissioned, as had been expected. Significantly, plutonium’s half-life, the time it took for half a sample to decay away, was over 24 thousand years, which meant it could be stored indefinitely inside a weapon. The military implications were obvious: plutonium was a viable alternative fuel to uranium-235 that could be used to make an atomic bomb.
Six months later, on October 9, 1941, two months before the attack on Pearl Harbor, Bush conferred with President Roosevelt and Vice-President Henry Wallace and asked permission to formally begin an atomic program. They discussed its likelihood of success and what little was known of the German uranium project. Then Roosevelt gave Bush the go-ahead and directed him to expedite an atomic program in every possible way.
“MAUD Report,” March 1941, The Department of Energy, Office of History and Heritage Resources.