In 1942 he joined the Manhattan Project at the University of Chicago, where he was recruited by Enrico Fermi to join the effort to build the first nuclear reactor, having been recommended as a theory resource by Oppenheimer. When Oppenheimer formed the Manhattan Project's Los Alamos Laboratory in 1943, Christy was one of the early recruits to join the Theory Group. Christy is generally credited with the insight that a solid sub-critical mass of plutonium could be explosively compressed into supercriticality, a great simplification of earlier concepts of implosion requiring hollow shells. For this insight the solid-core plutonium model is often referred to as the "Christy pit".
After the war, Christy briefly joined the University of Chicago Physics department before being recruited to join the Caltech faculty in 1946 when Oppenheimer decided it was not practical for him to resume his academic activities. He stayed at Caltech for his academic career, serving as Department Chair, Provost and Acting President. In 1960 Christy turned his attention to astrophysics, creating some of the first practical computation models of stellar oscillations. For this work Christy was awarded the Eddington Medal of the Royal Astronomical Society in 1967. In the 1980s and 1990s Christy participated in the National Research Council's Committee on Dosimetry, an extended effort to better understand the actual radiation exposure due to the bombs dropped on Japan, and on the basis of that learning, better understand the medical risks of radiation exposure.
Early life
Robert Frederick Cohen was born on May 14, 1916, in Vancouver, British Columbia,[2] the son of Moise Jacques Cohen, an electrical engineer, and his wife Hattie Alberta née Mackay, a school teacher. He was named Robert after his maternal great uncle Robert Wood, and Frederick after Frederick Alexander Christy, the second husband of his maternal grandmother. He had an older brother, John, who was born in 1913. Moise changed the family surname to Christy by deed poll on August 31, 1918. On November 4, Moise was accidentally electrocuted at work.[3] Hattie died after goitre surgery in 1926. Christy and his brother were then cared for by Robert Wood, their grandmother Alberta Mackay, and their great aunt Maud Mackay.[4]
Christy was educated at Magee High School, and graduated in 1932 with the highest examination score in the province of British Columbia. He was awarded the Governor General's Academic Medal, and, importantly in view of his family's limited ability to pay, free tuition to attend the University of British Columbia (UBC). At the award dinner he met the second-place winner, Dagmar Elizabeth von Lieven, whom he dated while at UBC.[5] He received his Bachelor of Arts (BA) degree in mathematics and physics with first class honors in 1935, and his Master of Arts (MA) degree in 1937,[6][7] writing a thesis on "Electron attachment and negative ion formation in oxygen".[8]
George Volkoff, a friend of Christy who was a year ahead of him at UBC, was accepted as a graduate student at the University of California, Berkeley, by Robert Oppenheimer, who led the most active school of theoretical physics in the United States at that time. This inspired Christy to apply to the University of California as well. He was accepted, and was awarded a fellowship for his first year. At Berkeley he shared an apartment with Volkoff, Robert Cornog, Ken McKenzie and McKenzie's wife Lynn McKenzie.[9] For his thesis, Oppenheimer had him look at mesotrons, subatomic particles called muons today, that had recently been found in cosmic rays. They were so-called because they were more massive than electrons but less massive than protons. With the help of Shuichi Kusaka he performed detailed calculations of the particle's spin. He published two papers on mesotrons with Kusaka in the Physical Review,[10][11] which formed the basis of his 1941 Doctor of Philosophy (PhD) thesis [12]
Manhattan Project
Robert Christy's wartime Los Alamos security badge
Christy could have graduated in 1940, but could not then be a teaching assistant, and this would have left him jobless and without income.[13] In 1941, Oppenheimer found him a post at the physics department at Illinois Institute of Technology (IIT).[14] In May 1941, he married Dagmar von Lieven. They had two sons: Thomas Edward (Ted), born in 1944,[15] and Peter Robert, born in 1946.[16] IIT paid Christy $200 per month to teach 27 hours per week for 11 months per annum. To keep abreast of developments in physics, he attended seminars at the University of Chicago.[14] This brought him to the attention of Eugene Wigner, who hired him for the same money that IIT was paying him but as a full-time research assistant, commencing in January 1942.[17]
A model of a Christy pit
Enrico Fermi and his team from Columbia University arrived at the University of Chicago in January 1942 as part of an effort to concentrate the Manhattan Project's reactor work at the new Metallurgical Laboratory.[18] Fermi arranged with Wigner for Christy to join his group,[19] which was building a nuclear reactor, which Fermi called a "pile", in the squash court under Stagg Field at the University of Chicago. Construction began on November 6, 1942, and Christy was present when Chicago Pile-1 went critical on December 2.[20][21]
In early 1943, Christy joined Oppenheimer's Los Alamos Laboratory in New Mexico,[22] where he became an American citizen in 1943 or 1944.[23][24]Hans Bethe, the head of T (Theoretical) Division, detailed his physicists to assist with the projects at the laboratory. With his knowledge of reactors, Christy's assignment was to help Donald W. Kerst's Water Boiler group.[25] The Water Boiler was an aqueous homogeneous reactor intended as a laboratory instrument to test critical mass calculations and the effect of various tamper materials. It was the first reactor to use enriched uranium as a fuel, and the first to use liquid fuel in the form of soluble uranium sulfate dissolved in water. Christy estimated that it would require 600 grams (21oz) of pure uranium-235, a figure he subsequently revised to 575 grams (20.3oz). When the reactor went critical on May 9, 1944, with 565 grams (19.9oz), the accuracy of Christy's figures raised the laboratory's confidence in T Division's calculations.[26]
The discovery by Emilio Segrè's group in April and May 1944 of high levels of plutonium-240 in reactor-produced plutonium meant that an implosion-type nuclear weapon was required, but studies indicated that this would be extremely difficult to achieve. [27] By August 1944, the calculations had been made of how an ideal spherical implosion would work; the problem was how to make it work in the real world where jets and spalling were a problem. Christy worked in Rudolf Peierls's T-1 Group, which studied the theory of implosion. He suggested the possibility of using a solid plutonium core that would form a critical mass when compressed. This was an ultra-conservative design that solved the problem of jets by brute force. It became known as the "Christy pit" or "Christy gadget", "gadget" being the laboratory euphemism for a bomb.[28] However the solid pit was intrinsically less efficient than a hollow pit, and it required a modulated neutron initiator to start the chain reaction.[29] Christy worked with Klaus Fuchs, Paul Stein and Hans Bethe to develop a suitable initiator design, which became known as an "urchin".[30]The Gadget used in the Trinity nuclear test and the Fat Man used in the atomic bombing of Nagasaki used Christy pits.[6]
Later in life, Christy agreed to give a number of both oral history and video interviews in which he discussed his role in the Manhattan Project and latter interests.[31][32]
Later life
An artist's conception of the Project Orion spacecraft
After the war ended, Christy accepted an assistant professorship at the University of Chicago, at a salary of $5,000 per annum, twice what he had been making before the war. He moved back to Chicago in February 1946, but suitable housing was hard to find in the immediate post-war period, and Christy and his family shared a mansion with Edward Teller and his family.[33]
Before the war, Oppenheimer had spent part of each year teaching at California Institute of Technology (Caltech). Christy was one of Oppenheimer's Berkeley students who made the trip down to Pasadena, California, each year to continue studying with Oppenheimer.[34] After the war, Oppenheimer decided that with his additional responsibilities he could no longer continue this arrangement. The head of the W. K. Kellogg Radiation Laboratory at Caltech, Charles Lauritsen therefore asked Oppenheimer for the name of a theoretical physicist that he would recommend as a replacement. Oppenheimer recommended Christy. Willy Fowler then approached Christy with an offer of a full-time position at Caltech at $5,400 per annum, and Christy accepted. He remained at Caltech for the rest of his academic career. The drawback to working at Caltech was that neither Lauritsen nor Fowler was a theoretical physicist, so a heavy workload fell on Christy. This was recognised by a pay raise to $10,000 per annum in 1954.[35]
Christy joined Oppenheimer, Lauritsen and Robert Bacher, who joined the faculty at Caltech in 1949, in Project Vista, a detailed 1951 study on how Western Europe could be defended against the Soviet Union.[36] Christy was distraught at the outcome of the 1954 Oppenheimer security hearing. When he encountered Teller, who had testified against Oppenheimer, at Los Alamos in 1954, Christy publicly refused to shake Teller's hand.[37] "I viewed Oppenheimer as a god", he later recalled, "and I was sure that he was not a treasonable person."[2] Asked about his relationship with Teller in 2006, Christy said:
I’ve seen him from time to time. Our relationship has remained cool. Since that time, I have disagreed with him in a number of areas. For example, the Strategic Defense Initiative. I have disagreed with him, but I have not argued with him publicly, because Teller operates at a much different level than I do. He’s a confidant of presidents; I’m not. As I say, I merely disagree privately, and that’s the way it is.[38]
In 1956, Christy was one of a number of scientists from Caltech who publicly called for a ban on atmospheric nuclear testing. The 1963 Partial Nuclear Test Ban Treaty that Christy advocated put an end to one of his most unusual projects. He worked with Freeman Dyson on Project Orion, the design of a spacecraft propelled by atomic bombs.[36]
Christy was appointed vice president and Provost of Caltech in 1970.[39] Under Christy and President Harold Brown Caltech expanded its humanities and added economics to allow (or perhaps to compel—undergrads were required to take 25% of their units in "humanities") students to broaden their education. He had David Morrisroe appointed as vice president for Financial Affairs, and they steered Caltech through the financially stringent 1970s. The first women were admitted as undergraduates in Fall 1970.[40]
When Jenijoy La Belle, who had been hired in 1969 but refused tenure in 1974, filed suit with the Equal Employment Opportunity Commission, Christy pressed for the case to be settled and La Belle to be given tenure. The EEOC ruled against Caltech in 1977, adding that she had been paid less than male colleagues. La Belle received tenure in 1979.[40]
In 1970 he became romantically involved with Inge-Juliana Sackman, a fellow physicist 26 years his junior.[41] He divorced Dagmar in early 1971,[39] and married Juliana on August 4, 1973.[42] They had two daughters, Illia Juliana Lilly Christy, born in 1974, and Alexandra Roberta (Alexa) Christy, born in 1976.[43]
Christy briefly became acting President of Caltech in 1977 when Brown left to become Secretary of Defense. Christy returned to teaching after Marvin L. Goldberger became president in 1978. He became Institute Professor of Theoretical Physics in 1983, and Institute Professor Emeritus in 1986.[36]
Christy died on October 3, 2012. He was survived by his wife Juliana, their two daughters, Illia and Alexa, and his two sons, Peter and Ted.[2] He was buried at Mountain View Cemetery in Altadena, California.[44]
↑ The episode during which "[...] Christy publicly refused to shake Teller's hand" is recounted in more detail (including [a link to, and] a 3-paragraph "block quote" from a 1994 Caltech "oral history" interview of Christy) here:
[QUOTE]: Well, my feelings were very strong. I told you earlier that in some sense I viewed Oppenheimer as a god. He was on a pedestal, and I looked up to him. And I was sure that he was not a treasonable person. I knew he had leftist contacts; that was well known to everyone. But I felt that it was just the wrong thing to do, for an honorable physicist to testify against Oppenheimer. It just wasn't right. And I was very upset by it. I still am. I felt, therefore, that it as [was] really improper, it was wrong. …
I ran into [Teller] not long afterward. We were both at Los Alamos—this was in the summertime. I remember that the Fuller Lodge was where they had an eating establishment. It was a fine, beautiful old log building. And there I was, eating. And I happened to see Edward Teller. I believe he approached me with his hand out to shake my hand. And I very deliberately refused to shake his hand. …
[I]t was a very deliberate action on my part—impulse, of course, because I didn't have time to plan this. And it was recognized by everyone else for what it was—that I refused to have a direct association with him. I think he was somewhat hurt. … I've seen him from time to time [since then]. Our relationship has remained cool.
Enrico Fermi was an Italian and naturalized American physicist, renowned for being the creator of the world's first artificial nuclear reactor, the Chicago Pile-1, and a member of the Manhattan Project. He has been called the "architect of the nuclear age" and the "architect of the atomic bomb". He was one of very few physicists to excel in both theoretical physics and experimental physics. Fermi was awarded the 1938 Nobel Prize in Physics for his work on induced radioactivity by neutron bombardment and for the discovery of transuranium elements. With his colleagues, Fermi filed several patents related to the use of nuclear power, all of which were taken over by the US government. He made significant contributions to the development of statistical mechanics, quantum theory, and nuclear and particle physics.
"Fat Man" was the codename for the type of nuclear weapon the United States detonated over the Japanese city of Nagasaki on 9 August 1945. It was the second and largest of the only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation marked the third nuclear explosion in history. The first one was built by scientists and engineers at Los Alamos Laboratory using plutonium manufactured at the Hanford Site and was dropped from the Boeing B-29 Superfortress Bockscar piloted by Major Charles Sweeney.
The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada. From 1942 to 1946, the project was directed by Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist J. Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the bombs. The Army program was designated the Manhattan District, as its first headquarters were in Manhattan; the name gradually superseded the official codename, Development of Substitute Materials, for the entire project. The project absorbed its earlier British counterpart, Tube Alloys, and subsumed the program from the American civilian Office of Scientific Research and Development. The Manhattan Project employed nearly 130,000 people at its peak and cost nearly US$2 billion, over 80 percent of which was for building and operating the plants that produced the fissile material. Research and production took place at more than 30 sites across the US, the UK, and Canada.
Edward Teller was a Hungarian-American theoretical physicist and chemical engineer who is known colloquially as "the father of the hydrogen bomb" and one of the creators of the Teller–Ulam design based on Stanisław Ulam's design.
J. Robert Oppenheimer was an American theoretical physicist who served as the director of the Manhattan Project's Los Alamos Laboratory during World War II. He is often called the "father of the atomic bomb" for his role in overseeing the development of the first nuclear weapons.
Stanisław Marcin Ulam was a Polish mathematician, nuclear physicist and computer scientist. He participated in the Manhattan Project, originated the Teller–Ulam design of thermonuclear weapons, discovered the concept of the cellular automaton, invented the Monte Carlo method of computation, and suggested nuclear pulse propulsion. In pure and applied mathematics, he proved a number of theorems and proposed several conjectures.
Edwin Mattison McMillan was an American physicist credited with being the first to produce a transuranium element, neptunium. For this, he shared the 1951 Nobel Prize in Chemistry with Glenn Seaborg.
Hans Albrecht Bethe was a German-American physicist who made major contributions to nuclear physics, astrophysics, quantum electrodynamics and solid-state physics, and received the Nobel Prize in Physics in 1967 for his work on the theory of stellar nucleosynthesis. For most of his career, Bethe was a professor at Cornell University.
Emilio Gino Segrè was an Italian and naturalized-American physicist and Nobel laureate, who discovered the elements technetium and astatine, and the antiproton, a subatomic antiparticle, for which he was awarded the Nobel Prize in Physics in 1959 along with Owen Chamberlain.
Robert Rathbun Wilson was an American physicist known for his work on the Manhattan Project during World War II, as a sculptor, and as an architect of the Fermi National Accelerator Laboratory (Fermilab), where he was the first director from 1967 to 1978.
Norris Edwin Bradbury, was an American physicist who served as director of the Los Alamos National Laboratory for 25 years from 1945 to 1970. He succeeded Robert Oppenheimer, who personally chose Bradbury for the position of director after working closely with him on the Manhattan Project during World War II. Bradbury was in charge of the final assembly of "the Gadget", detonated in July 1945 for the Trinity test.
Seth Henry Neddermeyer was an American physicist who co-discovered the muon, and later championed the implosion-type nuclear weapon while working on the Manhattan Project at the Los Alamos Laboratory during World War II.
Robert Fox Bacher was an American nuclear physicist and one of the leaders of the Manhattan Project. Born in Loudonville, Ohio, Bacher obtained his undergraduate degree and doctorate from the University of Michigan, writing his 1930 doctoral thesis under the supervision of Samuel Goudsmit on the Zeeman effect of the hyperfine structure of atomic levels. After graduate work at the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT), he accepted a job at Columbia University. In 1935 he accepted an offer from Hans Bethe to work with him at Cornell University in Ithaca, New York. It was there that Bacher collaborated with Bethe on his book Nuclear Physics. A: Stationary States of Nuclei (1936), the first of three books that would become known as the "Bethe Bible".
The Manhattan Project was a research and development project that produced the first atomic bombs during World War II. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army Corps of Engineers. The Army component of the project was designated the Manhattan District; "Manhattan" gradually became the codename for the entire project. Along the way, the project absorbed its earlier British counterpart, Tube Alloys. The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US$2 billion. Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons.
"Thin Man" was the code name for a proposed plutonium-fueled gun-type nuclear bomb that the United States was developing during the Manhattan Project. Its development was abandoned in 1944 after it was discovered that the spontaneous fission rate of nuclear reactor-bred plutonium was too high for use in a gun-type design due to the high concentration of the isotope plutonium-240.
Joseph William Kennedy was an American chemist who co-discovered plutonium, along with Glenn T. Seaborg, Edwin McMillan, and Arthur Wahl. During World War II, he led the CM Division at the Manhattan Project's Los Alamos Laboratory, where he oversaw research onto the chemistry and metallurgy of uranium and plutonium. After the war, he was recruited as a professor at Washington University in St. Louis, where he is credited with transforming a university primarily concerned with undergraduate teaching into one that also boasts strong graduate and research programs.
Donald William Kerst was an American physicist who worked on advanced particle accelerator concepts and plasma physics. He is most notable for his development of the betatron, a novel type of particle accelerator used to accelerate electrons.
Joseph Oakland Hirschfelder was an American physicist who participated in the Manhattan Project and in the creation of the nuclear bomb.
Marshall Glecker Holloway was an American physicist who worked at the Los Alamos Laboratory during and after World War II. He was its representative, and the deputy scientific director, at the Operation Crossroads nuclear tests at Bikini Atoll in the Pacific in July 1946. Holloway became the head of the Laboratory's W Division, responsible for new weapons development. In September 1952 he was charged with designing, building and testing a thermonuclear weapon, popularly known as a hydrogen bomb. This culminated in the Ivy Mike test in November of that year.
The Los Alamos Laboratory, also known as Project Y, was a secret scientific laboratory established by the Manhattan Project and overseen by the University of California during World War II. It was operated in partnership with the United States Army. Its mission was to design and build the first atomic bombs. Robert Oppenheimer was its first director, serving from 1943 to December 1945, when he was succeeded by Norris Bradbury. In order to enable scientists to freely discuss their work while preserving security, the laboratory was located on the isolated Pajarito Plateau in Northern New Mexico. The wartime laboratory occupied buildings that had once been part of the Los Alamos Ranch School.
References
Christy, I.-Juliana (2013). Achieving the Rare: Robert F. Christy's Journey in Physics and Beyond. Singapore: World Scientific. ISBN978-981-4460-24-8.
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