At the same time that the key discoveries in neutron physics and neutron reactions were occurring (see Invention and Discovery: Atomic Bombs and Fission, the political situation around the world was deteriorating. The two key developments were of course:
The rush of ominous events is too thick to enumerate in a brief overview but some principal ones are:
It is against this background that Szilard fretted about the possibility of an atomic bomb. The discovery of fission came just as Germany was girding itself to abandon expansion by intimidation and resort to armed conquest.
World War II erupted at a moment when the promise of atomic energy had progressed from being possibile to being probable. It was not clear whether this energy could be released explosively however.
Szilard, as always, was both a man of vision and a man of action. Well known among European physicists, Szilard drafted a letter in consultation with Albert Einstein that was addressed from Einstein to President F.D. Roosevelt and which warned hime of the possibility of nuclear weapons (the "Einstein Letter"). This letter was delivered to FDR on October 11, 1939, and ten days later the first meeting of the Advisory Committee on Uranium (the "Briggs Uranium Committee") was held in Washington, DC on Pres. Roosevelt's order.Szilard and Einstein Together After the War
Due largely to persistent official lack of interest, the progress on the subject was desultory and inconclusive in the United States. The next key developments occurred in the United Kingdom.
During February 1940, expatriot physicists Otto Frisch and Rudolf Peierls, living in the UK prepared a theoretical analysis of the possibility of fast fission in U-235. Their report contains the first well grounded (although rough) estimates of the size of a critical mass ("a pound or two") and probable efficiency, and proposed practical schemes for bomb design and the production of U-235. This "roadmap" for fission weapon development would be elaborated upon and modified to a spectacular degree in the coming years, but it remains basically sound.
So persuasive is the report by Frisch and Rudolf Peierls' that a study committee is formed at the highest levels of goverment (eventually code-named the MAUD Committee) on April 10. By December the MAUD Committee would issue a key report selecting gaseous diffusion as the most promising method of uranium enrichment.
Through 1940 and well into 1941, work accelerated in the U.S., and important discoveries accumulated although official interest and support languished. In February, 1941 Philip Abelson began actual development of a practical uranium enrichment system (liquid thermal diffusion) and on February 26 Glenn Seaborg and Arthur Wahl discover plutonium. During March the first American measurements of the U-235 fission cross section allow Peierls to calculate the first experimentally supported estimate of a critical mass for U-235 (18 lb as a bare sphere, 9-10 lb when surrounded by a reflector).
By July 1941 plutonium was demonstrated to be a superior fissile material, and the MAUD Committee completed its final report, describing atomic bombs and project propsals for building them in some technical detail.
On September 3, 1941, with PM Winston Churchill's endorsement, the British Chiefs of Staff agree to begin development of an atomic bomb. But it is not until December 18, after months of bureaucratic struggling and the U.S. entry into the war, that a U.S. project to investigate atomic weapons (as opposed to "study fission") finally gets underway.
This Manhattan Project predecessor, code named the S-1 project, was headed by Arthur H. Compton. The core group of scientists that would lead the development of the atomic bomb had coalesced well before this, and was already working as hard as resources allowed on the problem.
In January 1942, Enrico Fermi's on-going work with graphite and uranium was transferred to a new secret project, code named the Metallurgical Laboratory (Met Lab) at the University of Chicago. In April Fermi begins design of CP-1, the world's first (human built) nuclear reactor.
Throughout early and mid 1942, fundamental neutron physics research proceeded, as did work on developing industrial scale processes for producing fissile materials. But it became increasingly obvious that since this was to be an industrial scale project, a proven project manager was called for. Furthermore, since it was a weapons project, it need to be brought under an organization experienced in producing weapons.
On June 18, 1942 Brig. Gen. Steyr ordered Col. James Marshall to organize an Army Corps of Engineers District to take over and consolidate atomic bomb development. During August Marshall created a new District organization with the intentionally misleading name "Manhattan Engineer District" (MED), now commonly called "The Manhattan Project".
Despite its official founding in August, the Manhattan Project really began on September 17, 1942 when Col. Leslie Richard Groves was notified at 10:30 a.m. by Gen. Brehon Somervell that his assignment overseas had been cancelled. Groves, an experienced manager who had just overseen the collosal construction of the Pentagon, seized immediate and decisive control. In just two days he resolved issues that had dragged on for months under Compton. On September 18 Groves ordered the purchase of 1250 tons of high quality Belgian Congo uranium ore stored on Staten Island, and the next day purchased 52000 acres of land to be the future site of Oak Ridge. Groves was promoted to Brigadier General on September 23. By September 26 Groves had secured access to the highest emergency procurement priority then in existence (AAA).
The era of weak, indecisive leadership was over.
Groves' pushy, even overbearing, demeanor won him few friends among the scientists on the Manhattan Project (in particular a special enmity developed between Groves and Szilard). Many detested him at the time, considering him a boor and a buffoon. It was only after the war that many scientists began to appreciate how crucial his organizational and managerial genius was to the MED.
During the fall, while Fermi built CP-1 in Chicago, Groves took the fissile material programs out of the hands of the scientists and placed them under the management of industrial corporations like DuPont and the Kellog Corporation. He ordered construction begun immediately on the fissile material production plants, even though designs and plans had not yet been drawn up, realizing that the same basic site preparation work would be required no matter what.
On October 15, 1942 Groves asks Dr. J. Robert Oppenheimer to head Project Y, the new planned central laboratory for weapon physics research and design. The site for which he selected on November 16 at Los Alamos, New Mexico.Dr. J. Robert Oppenheimer (taken during 1945)
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|Oppenheimer and Groves inspecting the remains of the Trinity test tower, 9 September 1945. Despite his suit, in this picture you can sense how emaciated Oppenheimer had become during the Manhattan Project.|
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Oppenheimer, a professor of physics at Berkeley, had demonstrated a special skill at leading groups of scientists during the S-1 program, which Groves quickly took notice of. Oppenheimer and Groves developed a good relationship, each recognizing how critical the other was to the project.
On December 1, 1942, after 17 days of round-the-clock work Fermi's group completed CP-1 (sooner than planned) when Fermi projected that a critical configuration had been reached. It contained 36.6 metric tons of uranium oxide, 5.6 metric tons of uranium metal, and 350 metric tons of graphite.
On December 2, 1942 - 3:49 p.m. CP-1 went critical and was allowed to reach a thermal output of 0.5 watts (ultimately it was operated up to a maximum power level of 200 watts).
In January, 1943 Groves acquired the Hanford Engineer Works, 780 square miles of land on the Columbia River in Washington for plutonium production reactors and separation plants. During March Los Alamos began operations as the staff arrived.
During the remainder of 1943, work continued on the construction of the plutonium production facilities (reactors and chemical processing) at Hanford, and the uranium enrichment plants (gaseous diffusion and electromagnetic separation) at Oak Ridge. A large experimental graphite reactor (the X-10) was also constructed at Oak Ridge to provide research quantities of plutonium, and went critical on November 4. Refinement of gun-assembly based weapon designs continued at Los Alamos. Preliminary implosion research also proceeded, initially at a low level of effort, but after promising early results at an accelerated rate late in the year.
The first attempt at large scale uranium enrichment, the electromagnetic Alpha tracks at Oak Ridge, went on-line in the fall, but failed completely. By the end of the year complete rebuilding was ordered.
Also in the fall, Project Alberta began. Its purpose was to prepare for the actual combat delivery of atomic weapons by conducting weapons delivery tests, modifying aircraft for carrying the atomic weapons, and organizing and training flight crews and field teams for weapons handling.
In 1944 work proceeded on all fronts:
In January a major problem surfaced with the diffusion barriers intended for the K-25 gaseous diffusion plant at Oak Ridge. The process then being developed for barrier production seemed unpromising, and Groves to switched planned production to a new process creating months of delays in equipping K-25 for operation. Abelson, then in the process of constructing a thermal diffusion uranium enrichment plant, learned about the problems with the Manhattan Project's gaseous diffusion plant, and leaked information about his technology to Oppenheimer.
On April 5 the first sample of X-10 reactor produced plutonium arrived from Oak Ridge. Emilio Segre immediately began monitoring its spontaneous fission rate. By April 15 his preliminary estimate of a spontaneous fission rate indicated that it was far too high for gun assembly. The report was kept quiet due to limited statistics, and observations continued.
By mid-May 1944, six months after the start of accelerated implosion research, little progress towards successful implosion had been made. The experimental and theoretical work on the problem had been reorganized a number of times, and resources devoted to it kept expanding. New IBM calculating equipment was now being put to use. At this point two British scientists joined Los Alamos who had important impacts on the implosion program. Geoffrey Taylor (arrived May 24) pointed out implosion instability problems (especially the Rayleigh-Taylor instability), which ultimately led to a very conservative design to minimize possible instability problems. James Tuck brought the critical idea of explosive lenses for detonation wave shaping.
On June 3, after visiting the thermal diffusion uranium enrichment pilot plan at the Naval Research Laboratory, a team of Manhattan Project experts recommended that a plant be built to feed enriched material to the electromagnetic enrichment plant at Oak Ridge. On June 18 Groves contracted to have S-50, a liquid thermal diffusion uranium enrichment plant, built at Oak Ridge in no more than three months.
On July 4, 1944 Oppenheimer revealed Segre's spontaneous fission measurements to the Los Alamos staff. The neutron emission for reactor-produced plutonium was too high for gun assembly to work. The measured rate was 50 fissions/kg-sec, the fission rate in Hanford plutonium is expected to be over 100 times higher still.
This discovery was a turning point for Los Alamos, the Manhattan Project, and eventually for the practice of large scale science after the war. The planned plutonium gun had to be abandoned, and Oppenheimer was forced to make implosion research a top priority, using all available resources to attack it. A complete reorganization of Los Alamos Laboratory was required. With just 12 months to go before expected weapon delivery a new fundamental technology, explosive wave shaping, had to be invented, made reliable, and a enormous array of engineering problems had to be solved. During this crisis many foundations for post-war science were laid. Scientist- administrators (as opposed to academic or research scientists) came to the forefront for running large scale research efforts. Automated numerical techniques (as opposed to manual analytical ones) were applied to solve important scientific problems, not just engineering applications. The dispersal of key individuals after the end of the war later carried these insights, as well as the earlier organizational principles developed at Los Alamos throughout American academia and industry.
July 1, 1944 - The Manhattan Project was granted the highest project-wide procurement priority (AA-1).
July 20, 1944 - The Los Alamos Administrative Board decided on a reorganization plan to direct the laboratory's full resources on implosion. Instead of being organized around scientific and engineering areas of expertise, all work was organized around whether it applied to implosion, or the uranium gun weapon, with the former receiving most of the resources. The reorganization was completed in less than two weeks.
During August Groves made his first estimate of bomb availability since the beginning of the Manhattan Project (the estimate was mid-spring 1945). Also this month the Air Force began modifying 17 B-29s for combat delivery of atomic weapons.Alpha Tracks at Y-12 The Alpha Track Control Room
September 1944 marked a difficult period:
Then, a new crisis struck the plutonium production effort. On September 26 the first full scale plutonium reactor, the B pile, at Hanford was completed and loaded with uranium. This reactor contained 200 tons of uranium metal, 1200 tons of graphite, and was cooled by 5 cubic meters of water/sec. It was designed to operate at 250 megawatts, producing some 6 kg of plutonium a month. On this day Fermi supervised reactor's first start-up. After several hours of operation at 100 megawatts, the B pile inexplicably shut down, then started up again by itself the next day. Within a few days this was determined to be due to poisoning by the highly efficient neutron absorber Xenon-135, a radioactive fission product. The B reactor, and others under construction, had to be modified to add extra reactivity to overcome this effect before production could begin.
October 27, 1944 - Oppenheimer approved plans for a bomb test in the Jornada del Muerto valley at the Alamagordo Bombing Range. Groves approved the plan 5 days later, provided that the test be conducted in Jumbo.
By the end of the year things start looking up;
By the start of 1945 the Manhattan Project had 'turned the corner'. The uranium bombs seemed assured of success in a matter of months. The prospects for the plutonium bomb were looking up although meeting an August 1 deadline imposed by Groves was far from certain. However, allied military successes against Germany and Japan made it a horse race to see whether it would matter to the war effort.
The K-25 Plant
|The 100 Ton Test|
July, 1945: Final preparations began at the New Mexico test site, the Jornada del Muerto at the Alamagordo Bombing Range, for the first atomic bomb test, code named Trinity. The date was set for July 16.