Manhattan Project

Though it involved over thirty different research and production sites, the Manhattan Project was largely carried out in three secret scientific cities that were established by power of eminent domain: Hanford, Washington, Los Alamos, New Mexico, and Oak Ridge, Tennessee. Some families in Tennessee were given two weeks notice to vacate the family farm lands they had possessed for generations. The Los Alamos lab was built on a mesa that previously hosted the Los Alamos Ranch School, a private residential boys school that featured the outdoors and horses (famous alumni included William Burroughs). The Hanford site, which grew to almost 1000 square miles (2,600 km²), incorporated land from some farms and two small towns, Hanford and White Bluffs. The existence of these cities was officially kept secret until the end of the war.

The Project culminated in the design, production, and detonation of three nuclear weapons in 1945. The first was on July 16: "Trinity", the world's first nuclear test, near Alamogordo, New Mexico. The second was the weapon "Little Boy", detonated on August 6, over the city of Hiroshima, Japan. The third was the weapon "Fat Man", detonated on August 9, over the city of Nagasaki, Japan.

The three primary sites of the project exist today as Hanford Site, Los Alamos National Laboratory, and Oak Ridge National Laboratory. By 1945, the Project employed over 130,000 people at its peak and cost a total of nearly $2 billion USD ($21 billion in 1996 dollars [1]).

History

Early ideas on nuclear energy

Enrico Fermi recalled the beginning of the project in a speech given in 1954 when he retired as President of the APS.

I remember very vividly the first month, January 1939, that I started working at the Pupin Laboratories because things began happening very fast. In that period, Niels Bohr was on a lecture engagement in Princeton and I remember one afternoon Willis Lamb came back very excited and said that Bohr had leaked out great news. The great news that had leaked out was the discovery of fission and at least the outline of its interpretation. Then, somewhat later that same month, there was a meeting in Washington where the possible importance of the newly discovered phenomenon of fission was first discussed in semi-jocular earnest as a possible source of nuclear power.

Roosevelt created an ad hoc Uranium Committee under the chairmanship of National Bureau of Standards chief Lyman Briggs. It began small research programs in 1939 at the Naval Research Laboratory in Washington, where physicist Philip Abelson explored uranium isotope separation. At Columbia University Italian-born nuclear physicist Enrico Fermi built prototype nuclear reactors using various configurations of graphite and uranium.

Vannevar Bush, director of the Carnegie Institution of Washington, organized the National Defense Research Committee in 1940 to mobilize the United States' scientific resources in support of the war effort.

New laboratories were created, including the Radiation Laboratory at the Massachusetts Institute of Technology, which aided the development of radar, and the Underwater Sound Laboratory at San Diego, which developed sonar.

The National Defense Research Council (NDRC) also took over the uranium project, as Briggs' program in nuclear physics was called. In 1940, Bush and Roosevelt created the Office of Scientific Research and Development to expand these efforts.

The uranium project had not made much progress by the spring of 1941, when word came from Britain of calculations by Otto Frisch and Fritz Peierls. The report, prepared by the so-called MAUD Committee, itself a sub-committee of the Committee for the Scientific Survey of Air Warfare under G.P. Thomson, professor of physics at Imperial College, London, showed that a very small amount of the fissionable isotope of uranium, U-235 - could produce an explosion equivalent to that of several thousand tons of TNT.

The National Academy of Sciences proposed an all-out effort to build nuclear weapons. Bush created a special committee, the S-1 Committee, to guide the effort. This happened to be on the day before the Japanese attack on Pearl Harbor, which was on December 7th, 1941, and meant the start of the war for the United States.

At the University of Chicago Metallurgical Laboratory, the University of California Radiation Laboratory and Columbia University's physics department, efforts to prepare the nuclear materials for a weapon were accelerated. Uranium 235 had to be separated from uranium ore and plutonium made by neutron bombardment of natural uranium. Beginning in 1942, huge plants were built at Oak Ridge (Site X) in Tennessee and Hanford (Site W) outside of Richland, Washington, to produce these materials.

When the United States entered World War II in December 1941, several projects were under way to investigate the separation of fissionable uranium 235 from uranium 238, the manufacture of plutonium, and the feasibility of nuclear piles and explosions.

Physicist and Nobel laureate Arthur Holly Compton organized the Metallurgical Laboratory at the University of Chicago in early 1942 to study plutonium and fission piles. Compton asked theoretical physicist J. Robert Oppenheimer of the University of California to take over research on fast neutron calculations, essential to the feasibility of a nuclear weapon. John Manley, a physicist at the University of Chicago Metallurgical Laboratory, was assigned to help Oppenheimer find answers by coordinating and contacting several experimental physics groups scattered across the country.

In the spring of 1942, Oppenheimer and Robert Serber of the University of Illinois, worked on the problems of neutron diffusion (how neutrons moved in the chain reaction) and hydrodynamics (how the explosion produced by the chain reaction might behave).

To review this work and the general theory of fission reactions, Oppenheimer convened a summer study at the University of California, Berkeley in June 1942. Theorists Hans Bethe, John Van Vleck, Edward Teller, Felix Bloch, Emil Konopinski, Robert Serber, Stanley S. Frankel, and Eldred C. Nelson (the latter three all former students of Oppenheimer) concluded that a fission bomb was feasible. The scientists suggested that such a reaction could be initiated by assembling a critical mass - an amount of nuclear explosive adequate to sustain it - either by firing two subcritical masses of plutonium or uranium 235 together or by imploding (crushing) a hollow sphere made of these materials with a blanket of high explosives. (Serber credits an early idea of implosion to Tolman). Until the numbers were better known, this was all that could be done.

Teller saw another possibility: By surrounding a fission bomb with deuterium and tritium, a much more powerful "superbomb" (which he called simply, the "Super") might be constructed. This concept was based on studies of energy production in stars made by Bethe before the war. When the detonation wave from the fission bomb moved through the mixture of deuterium and tritium nuclei, they would fuse together to produce much more energy than fission could, in the process of nuclear fusion, just as elements fused in the sun produce light and heat.

Bethe was skeptical, and as Teller pushed hard for his "superbomb", and proposed scheme after scheme, Bethe refuted each one. The idea had to be put aside while the fission bombs, and the war, were completed. (The "super", or thermonuclear device, was produced after the war and tested in 1952, after an acrimonious political fight pitting Teller against Oppenheimer, leading to loss of Oppenheimer's official status, and using methods different than Teller's specific ideas, which Bethe was correct in refuting.)

Teller also raised the speculative possibility that an atomic bomb might "ignite" the atmosphere, due to a hypothetical fusion reaction of nitrogen nuclei. Bethe showed, according to Serber, theoretically that it couldn't happen; in his book The Road from Los Alamos, Bethe says a refutation was written by Konopinski, C. Marvin, and Teller as report LA-602 (declassified Feb. 1973 online), showing that it was impossible, not just unlikely. In Serber's account, Oppenheimer unfortunately mentioned it to Arthur Compton, who "didn't have enough sense to shut up about it. It somehow got into a document that went to Washington" which lead to the question "never [being] laid to rest". In Bethe's account, this ultimate catastrophe came up again in 1975 when it appeared in a magazine article by H. C. Dudley, who got the idea from a report by Pearl Buck of an interview she had with Arthur Compton in 1959, where she completely misunderstood Compton! The worry was not entirely extinguished in some people's minds until the Trinity test; though if Bethe had been wrong, we would never know.

The summer conferences, the results of which were later summarized by Serber in "The Los Alamos Primer" (LA-1 online), provided the original theoretical basis for the design of the atomic bomb, which was to become the principal task at Los Alamos during the war, and the idea of the H-bomb, which was to haunt the Laboratory in the postwar era. Seldom has a physics summer school been as portentous for the future of mankind.

The measurements of the interactions of fast neutrons with the materials in a bomb are essential because the number of neutrons produced in the fission of uranium and plutonium must be known, and because the substance surrounding the nuclear material must have the ability to reflect, or scatter, neutrons back into the chain reaction before it is blown apart in order to increase the energy produced. Therefore, the neutron scattering properties of materials had to be measured to find the best reflectors.

Estimating the explosive power required knowledge of many other nuclear properties, including the cross section (a measure of the probability of an encounter between particles that result in a specified effect) for nuclear processes of neutrons in uranium and other elements. Fast neutrons could only be produced in particle accelerators, which were still relatively uncommon instruments in physics departments in 1942.

The need for better coordination was clear. By September 1942, the difficulties involved with conducting preliminary studies on nuclear weapons at universities scattered throughout the country indicated the need for a laboratory dedicated solely to that purpose. The need for it, however, was overshadowed by the demand for plants to produce uranium-235 and plutonium - the fissionable materials that would provide the nuclear explosives.

Vannevar Bush, the head of the civilian Office of Scientific Research and Development (OSRD), asked President Franklin Roosevelt to assign the large-scale operations connected with the quickly growing nuclear weapons project to the military. Roosevelt chose the Army to work with the OSRD in building production plants. The Army Corps of Engineers selected Col. James Marshall to oversee the construction of factories to separate uranium isotopes and manufacture plutonium for the bomb.

OSRD scientists had explored several methods to produce plutonium and separate uranium-235 from uranium, but none of the processes was ready for production - only microscopic amounts had been prepared.

Only one method - electromagnetic separation, which had been developed by Ernest Lawrence at the University of California Radiation Laboratory at the University of California, Berkeley - seemed promising at the time for large-scale production. But scientists could not stop studying other potential methods of producing fissionable materials, because it was so expensive and because it was unlikely that it alone could produce enough material before the war was over.

Marshall and his deputy, Col. Kenneth Nichols, had to struggle to understand both the processes and the scientists with whom they had to work. Thrust suddenly into the new field of nuclear physics, they felt unable to distinguish between technical and personal preferences. Although they decided that a site near Knoxville, Tenn., would be suitable for the first production plant, they didn't know how large the site had to be and so put off its acquisition. There were other problems, too.

Because of its experimental nature, the nuclear weapons work could not compete with the Army's more-urgent tasks for top-priority ratings. The selection of scientists' work and production-plant construction often were delayed by Marshall's inability to get the critical materials, such as steel, that also were needed in other military productions.

Even selecting a name for the new Army project was difficult. The title chosen by Gen. Brehon Somervell, "Development of Substitute Materials," was objectionable because it seemed to reveal too much.

The Manhattan Engineering District

The first thing he did was rechristen the project The Manhattan District. The name evolved from the Corps of Engineers practice of naming districts after its headquarters' city (Marshall's headquarters were in New York City). At the same time, Groves was promoted to brigadier general, which gave him the rank thought necessary to deal with the senior scientists in the project.

Within a week of his appointment, Groves had solved the Manhattan Project's most urgent problems. His forceful and effective manner was soon to become all too familiar to the atomic scientists.

The first major scientific hurdle of the project was solved on December 2, 1942 below the bleachers of Stagg Field at the University of Chicago. Then and there a team led by Enrico Fermi initiated the first self-sustaining nuclear chain reaction. A coded phone call from Compton saying, "The Italian navigator (referring to Fermi) has landed in the new world, the natives are friendly" to Conant in Washington, DC, brought the news that the experiment was a success.

The two different paths to the bomb

The Hiroshima bomb, Little Boy, was based on uranium-235, a rare isotope of uranium that has to be physically separated from more prevalent uranium-238 isotope, which is not suitable for use in an explosive device. The separation was effected mostly by gaseous diffusion of uranium hexafluoride (UF₆), but also by other techniques, such as thermal diffusion, and the calutron method, using the mass spectrometer principle of magnetic separation. The bulk of this separation work was done at Oak Ridge. The bomb itself used the so-called "gun" mechanism to assemble a critical mass of the fissile U-235; one mass of U-235 was fired down a tube into another mass.

In contrast, the devices used in the first and only test, and also the Nagasaki bomb, Fat Man, consisted primarily of plutonium-239. This is a synthetic element which, in the form created by the reactors used to produce it, contains too much of an isotope which too readily undergoes fission for it to be used in gun type device. (The issue is that due to the relatively slow assembly speed of the gun type device, the bomb will "fizzle"; i.e. blow itself apart before it develops maximum power.) A so-called "implosion" device, in which a sphere of fissile material was collapsed on itself, promised faster assembly, and thus offered a solution to the problem. The design of an implosion device was at the center of the efforts by physicists at Los Alamos during the Project.

The property of uranium-238 which makes it less suitable directly for use in an atomic bomb is used in the production of plutonium -- with sufficiently slow neutrons, uranium-238 will absorb neutrons and transmute into plutonium-239. The production and purification of plutonium was at the center of wartime, and post-war, efforts at the Hanford Site, using techniques developed in part by Glenn Seaborg.

The first live test of the plutonium bomb was on July 16, 1945, near Alamagordo, New Mexico, and was code-named "Trinity". "The energy developed in the test was several times greater than that expected by scientific group." (Official report)

Similar efforts

Together with the cryptographic efforts centered at Bletchley Park in England, Arlington Hall and the Naval Communications Annex (both in commandeered private girls' schools in Washington DC), and the development of microwave radar at MIT's Radiation Lab, the Manhattan Project represents one of few massive, secret, and outstandingly successful technological efforts spawned by the conflict of World War II.

The choice of civilian instead of military targets has often been criticized. However, the U.S. already had a policy of massive incendiary attacks against civilian targets in Japan. They dropped 20% explosives, to break up wooden structures and provide fuel, and then dropped 80% (by weight) small incendiary bombs to set the cities on fire. The resulting raids devastated many Japanese cities, including Tokyo, even before atomic weapons were deployed. The allies performed such attacks because Japanese industry was extremely dispersed among civilian targets (with many tiny family-owned factories operating in the midst of civilian housing), and in order to break the will of the Japanese population to back the war. Hiroshima had been spared conventional bombing so as to better gauge the effects of the nuclear bomb.

See also