Manhattan Project

Manhattan Project

The Manhattan Project was an effort during World War II in the United States to develop the first nuclear weapon. It was directed by American physicist Dr. Julius Robert Oppenheimer.

The industrial problem was centered around the production of sufficient fissile material, of sufficient purity. This effort was two-fold, and is represented in the two bombs that were dropped.

The Hiroshima bomb, Little Boy, was uranium-235, a minor isotope of uranium that has to be physically separated from more prevalent uranium-238, 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. The bulk of this separation work was done at Oak Ridge.

The Nagasaki bomb, Fat Man, in contrast, consisted primarily of plutonium-239, a synthetic element which could be induced to supercriticality only by implosion. 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 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. These 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 completely destroyed 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.

History

In the years between World War I and World War II, the United States had risen to pre-eminence in nuclear physics, driven by the work of recent immigrants and local physicists. These scientists had developed the basic tools of nuclear physics -- cyclotrons and other particle accelerators - and many new substances using these tools, including radioisotopes like carbon-14.

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.

US President Franklin D. Roosevelt was presented with a letter signed by Albert Einstein (transcribed by Leo Szilard) on October 11, 1939, which urged the United States to rapidly develop an atomic bomb program. The president agreed. The Navy awarded Columbia University the first Atomic Energy funding of $6,000, which grew into the Manhattan Project under Oppenheimer and Enrico Fermi's work.

Scientists in Germany discovered nuclear fission in late 1938. Refugee scientists Leo Szilard, Edward Teller and Eugene Wigner believed that the energy released in nuclear fission might be used in bombs by the Germans.

They persuaded Albert Einstein, America's most famous physicist, to warn President Franklin Roosevelt of this danger in an August 2, 1939, letter. In response to the warning, Roosevelt ordered increased research in nuclear physics.

Under the auspices of National Bureau of Standards chief Lyman Briggs, small research programs had begun in 1939 at the Naval Research Laboratory in Washington, where physicist Philip Abelson explored uranium isotope separation. At Columbia University Italian 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 summer of 1941, when word came from Britain of calculations by Otto Frisch and Fritz Peierls that 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. No sooner was this decision made than the Japanese bombed Pearl Harbor on December 7th, 1941. The war had begun 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 study the feasibility of a nuclear weapon.

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, Richard Tolman and Emil Konopinski 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. 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" 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, 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. When Teller raised the possibility that an atomic bomb might ignite the atmosphere, however, he kindled a worry that was not entirely extinguished until the Trinity test, even though Bethe showed, theoretically, that it couldn't happen.

The summer conferences, the results of which were later summarized by Serber in "The Los Alamos Primer" (LA-1), provided the 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.

With the prospect of a long war, a group of theorists under the direction of J. Robert Oppenheimer met at Berkeley during the summer of 1942 to develop preliminary plans for designing and building a nuclear weapon. Crucial questions remained, however, about the properties of fast neutrons. John Manley, a physicist at the University of Chicago Metallurgical Laboratory, was assigned to help Oppenheimer find answers to these questions by coordinating several experimental physics groups scattered across the country.

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 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 District

In the summer of 1942, Col. Leslie Groves was deputy to the chief of construction for the Army Corps of Engineers and had overseen construction of The Pentagon, the world's largest office building. Hoping for an overseas command, Groves objected when Somervell appointed him to take charge of the weapons project. His objections were overruled and Groves resigned himself to leading a project he thought had little chance of succeeding.

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.

In August 1942, the Manhattan Engineer District was created by the government to meet the goal of producing an atomic weapon under the pressure of ongoing global war. Its central mission became known as the Manhattan Project. Under the direction of Brigadier General Leslie Groves of the Army Corps of Engineers, who recently had supervised the construction of the Pentagon, secret atomic energy communities were created almost overnight in Oak Ridge, Tennessee, at Los Alamos, New Mexico, and in Hanford, Washington, to house the workers and gigantic new machinery needed to produce the bomb. The weapon itself would be built at the Los Alamos laboratory, under the direction of physicist J. Robert Oppenheimer.

Plucked from campuses around the country, medical researchers came face to face with the need to understand and control the effect upon the thousands of people, doctors included, of radioactive materials being produced in previously unimaginable quantities.

In November 1942 General Groves, through the intermediation of an Eastman Kodak official, paid a call on University of Rochester radiologist Stafford Warren. Rochester, like MIT and Berkeley, was another locale where radiation research had brought together physicists and physicians.

"They wanted to know what I was doing in radiation. So I discussed the cancer work and some of the other things," Warren told an interviewer in the 1960s. Then "[w]e got upstairs and they looked in the closet and they closed the transom and they looked out the window. . . . Then they closed and locked the door and said, 'Sit down.'"

Soon thereafter, Dr. Warren was made a colonel in the U.S. Army and the medical director of the Manhattan Project. As his deputy, Warren called on Dr. Hymer Friedell, a radiologist who had worked with Dr. Stone in California. Dr. Stone himself had meanwhile moved to the University of Chicago, where he would play a key role in Manhattan Project-related medical research.

Initially, researchers knew little or nothing about the health effects of the basic bomb components, uranium, plutonium, and polonium. But, as a secret history written in 1946 stated, they knew the tale of the radium dial painters:

The memory of this tragedy was very vivid in the minds of people, and the thoughts of potential dangers of working in areas where radiation hazards existed were intensified because the deleterious effects of radiation could not be seen or felt and the results of over-exposure might not become apparent for long periods after such exposure.

The need for secrecy, Stafford Warren later recalled, compounded the urgency of understanding and controlling risk. Word of death or toxic hazard could leak out to the surrounding community and blow the project's cover.

The need to protect the Manhattan Project workers soon gave rise to a new discipline, called health physics, which sought to understand radiation effects and monitor and protect nuclear worker health and safety. The Project was soon inundated with data from radiation-detection instruments, blood and urine samples, and physical exams. The "clinical study of the personnel," Robert Stone wrote in 1943, "is one vast experiment. Never before has so large a collection of individuals been exposed to so much radiation." Along with these data-gathering efforts came ethical issues.

Would disclosure of potential or actual harm to the workers, much less the public, impair the program? For example, a July 1945 Manhattan Project memo discussed whether to inform a worker that her case of nephritis (a kidney disease) may have been due to her work on the Project. The issue was of special import because, the memo indicated, the illness might well be a precursor of more cases. The worker, the memo explained, "is unaware of her condition which now shows up on routine physical check and urinalysis."

As this memo showed, there was an urgent need for decisions on how to protect the workers, while at the same time safeguard the security of the project: "The employees must necessarily be rotated out, and not permitted to resume further exposure. In frequent instances no other type of employment is available. Claims and litigation will necessarily flow from the circumstances outlined." There were also, the memo concluded, "Ethical considerations":

The feelings of the medical officers are keenly appreciated. Are they in accordance with their canons of ethics to be permitted to advise the patient of his true condition, its cause, effect, and probable prognosis? If not on ethical grounds, are they to be permitted to fulfill their moral obligations to the individual employees in so advising him? If not on moral grounds, are those civilian medical doctors employed here bound to make full disclosure to patients under penalty of liability for malpractice or proceeding for revocation of license for their failure to do so?

It is not clear what was decided in this case. However, the potential conflict between the government doctors' duty to those working on government projects and the same doctors' obligations to the government would not disappear. Following the war, as we see in chapter 12, this conflict would be sharply posed as medical researchers studied miners at work producing uranium for the nation's nuclear weapons.

Another basic question was the extent to which human beings could or should be studied to obtain the data needed to protect them. The radium dial painter data served as a baseline to determine how the effects of exposures in the body could be measured. But this left the question of whether plutonium, uranium, and polonium behaved more or less like radium. Research was needed to understand how these elements worked in the body and to establish safety levels. A large number of animal studies were conducted at laboratories in Chicago, Berkeley, Rochester, and elsewhere; but the relevance of the data to humans remained in doubt.

The Manhattan Project contracted with the University of Rochester to receive the data on physical exams and other tests from Project sites and to prepare statistical analyses. While boxes of these raw data have been retrieved, it is not clear what use was made of them. Accidents, while remarkably few and far between, became a key source of the data used in constructing an understanding of radiation risk. But accidents were not predictable, and their occurrence only enhanced the immediacy of the need to gain better data.

In 1944, the Manhattan Project medical team, under Stafford Warren and with the evident concurrence of Robert Oppenheimer, made plans to inject polonium, plutonium, uranium, and possibly other radioactive elements into human beings. As discussed in chapter 5, the researchers turned to patients, not workers, as the source of experimental data needed to protect workers. By the time the program was abandoned by the government, experimentation with plutonium had taken place in hospitals at the Universities of California, Chicago, and Rochester, and at the Army hospital in Oak Ridge, and further experimentation with polonium and uranium had taken place at Rochester.

The surviving documentation provides little indication that the medical officials and researchers who planned this program considered the ethical implications of using patients for a purpose that no one claimed would benefit them, under circumstances where the existence of the substances injected was a wartime secret. Following the war, however, the ethical questions raised by these experiments would be revisited in debates that themselves were long kept secret.

In addition to experimentation with internally administered radioisotopes, external radiation was administered in human experiments directed by Dr. Stone at Chicago and San Francisco and by others at Memorial Hospital in New York City. Once again, the primary subjects were patients, although some healthy subjects were also involved. In these cases, the researchers may have felt that the treatment was of therapeutic value to the patients. But, in addition to the question of whether the patients were informed of the government's interest, this research raised the question of whether the government's interest affected the patients' treatment. As discussed in chapter 8, these questions would recur when, beginning in 1951, and for two decades thereafter, the Defense Department would fund the collection of data from irradiated patients.

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