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A historical perspective, how science changed

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" All of us . . . knew that with the advent of the chain reaction, the world would never be the same again."
-Samuel K. Allison
UChicago physicist

The Atomic Age began at 3:25 p.m. on Dec. 2, 1942-quietly, in secrecy, on a squash court under the west stands of old Stagg Field at the University of Chicago.

Today, Henry Moore's "Nuclear Energy" sculpture and the Mansueto Library occupy the area at the corner of Ellis Avenue and 57 th Street where Enrico Fermi and his colleagues engineered the first controlled, self-sustaining nuclear chain reaction 70 years ago. Their experiment was a key step in the Manhattan Project to develop the atomic bomb during World War II.

That initial chain reaction was too weak to power even a single light bulb. It nevertheless transformed the world, and the University of Chicago along with it, in a range of endeavors spanning physics, chemistry, interdisciplinary research, policy analysis, and nuclear medicine. Even in 1942, those present at the historic event sensed how influential their work would be.

"All of us . . . knew that with the advent of the chain reaction, the world would never be the same again," former UChicago physicist Samuel K. Allison wrote at the time.

That first chain reaction's complex legacy includes the peaceful uses of nuclear energy, the terrible power of nuclear weapons, and a new era of other scientific and technological advances.

After the war, UChicago founded the Institute for Nuclear Studies and the Institute for the Study of Metals. Later renamed the Enrico Fermi and the James Franck institutes, they enabled the University to retain much of the intellectual talent that had assembled on campus to work on the Manhattan Project. Another outgrowth of the project was Argonne National Laboratory, which conducts basic and applied research in many major scientific disciplines. Today, Argonne is a partner in the Institute for Molecular Engineering, which is bringing leading scientists and engineers to a groundbreaking initiative to conduct research at the molecular level.

"What we see here is a legacy of connection that we're still building upon, a way to try to redefine engineering for the 21st century," said Provost Thomas Rosenbaum, the John T. Wilson Distinguished Service Professor in Physics.

Building the pile

Though Fermi's team was engaged in the biggest secret project of World War II, they discussed technical issues under a tree on the Main Quad, which they deemed safe from eavesdroppers. In the middle of the day on which they produced the first chain reaction, they took a customary lunch break at Hutchinson Commons.

"Don't imagine that they were able to achieve a chain reaction on the first try," says Roger Hildebrand, the Samuel K. Allison Distinguished Service Professor Emeritus in Physics. "They built and rebuilt stacks of uranium, uranium oxide, and graphite 30 times before they were ready for the final test."

Chicago Pile Number One, or CP-1 for short, consisted of 40,000 graphite blocks that enclosed 19,000 pieces of uranium metal and uranium oxide fuel. The scientists of what was then called the Metallurgical Laboratory, or "Met Lab," had arranged the graphite in layers within a 24-foot-square wooden framework.

Hildebrand had started his work on the Manhattan Project as an undergraduate chemistry major at the University of California, Berkeley. He worked for Nobel laureate Ernest Lawrence, namesake of the Lawrence Livermore and Lawrence Berkeley national laboratories, using Berkeley's cyclotron accelerator to transmute uranium into plutonium, an element believed to have potential for driving a chain reaction.

The samples irradiated in Berkeley and another lab in St. Louis ended up in the James Herbert Jones Laboratory, just one block south of old Stagg Field. There, in Jones Lab's Room 405, future Nobel laureate Glenn Seaborg achieved an important steppingstone on the way to the Atomic Age. He weighed the first visible, pinhead-sized sample of plutonium. It wasn't much, but enough to measure its chemical and metallurgical properties.

The potential hazards of nuclear power were evident even in those early days, but the war effort took priority. The Japanese had bombed Pearl Harbor on Dec. 7, 1941. Germany and Italy declared war on the United States four days later.

"They were advancing everywhere, they were conquering everywhere, and they were working on an atomic bomb," Hildebrand said of the Germans. "The consequence of losing a nuclear race was the preoccupation of everyone who knew that a nuclear bomb might be possible."

Outgrowths of chain reaction success

The scientific staff of the Metallurgical Laboratory founded the Atomic Scientists of Chicago on Sept. 26, 1945-just weeks after the United States dropped the atomic bomb on Hiroshima and Nagasaki. The group published the first issue of the Bulletin of the Atomic Scientists of Chicago on Dec. 10, 1945. The Bulletin 's Doomsday Clock still stands as a symbol of humanity's vulnerability to man-made catastrophe, with an agenda that expanded from nuclear weapons to include climate change and biological weapons.

Medical research gained unexpected benefits from the wartime research. In the early 1950s, the Atomic Energy Commission funded the Argonne Cancer Research Hospital, which became the Franklin McLean Institute, 5841 S. Ellis Ave., in 1973. The Argonne Hospital successfully pioneered the use of radiation in cancer treatment, with efforts later expanding to include radiological innovations in the diagnosis and treatment of other diseases.

Although the University of Chicago already was renowned in physics and chemistry before World War II, scientists who worked on the Manhattan Project helped those departments attain new research prominence following the war. Numerous UChicago scientists who were part of the war effort won Nobel Prizes for scholarly work in the postwar period, including Owen Chamberlain, Eugene P. Wigner, and Glenn Seaborg. Fermi, one of the most important scientists of the 20 th century, became an inspiring teacher at UChicago after the war before dying of stomach cancer in 1954. The National Accelerator Laboratory in Batavia was renamed in Fermi's honor in 1974, and became known as Fermilab, the site of numerous fundamental advances in particle physics.

UChicago builds for the future

Today, the William Eckhart Research Center is rising from a construction site directly across the street from where Fermi and his associates achieved the first controlled, self-sustaining nuclear chain reaction. The Eckhart Center will occupy the site of the former Research Institutes building, where Fermi and many other Manhattan Project veterans did transformative research.

UChicago scientists formally honored the Research Institutes' legacy in June 2011, when they publicly revealed the contents of the time capsule that Fermi had sealed within the Research Institutes building cornerstone nearly 62 years earlier. In retrospect the cornerstone's contents, which included booklets on the institutes and a sketch of their building, barely hinted at the accomplishments that would follow. That inspiring legacy survives to this day, said Robert Fefferman, dean of the University's Physical Sciences Division.

"This is not just something about the distant past," Fefferman, remarked at the cornerstone unveiling ceremony. "This is something that continues, and we're extremely proud of the grand tradition of science here."

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How the first chain reaction changed science

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" All of us . . . knew that with the advent of the chain reaction, the world would never be the same again." -Samuel K. AllisonUChicago physicist The Atomic Age began at 3:25 p.m. on Dec. 2, 1942-quietly, in secrecy, on a squash court under the west stands of old Stagg Field at the University of Chicago.

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Searchable database, excellent resources and audio clips

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Dedicated to supporting the Manhattan Project National Historical Park and capturing the memories of the people who harnessed the energy of the atom.

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The Einstein Letter

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Weapons and Power

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History of Nuclear Energy - World Nuclear Association

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Outline History of Nuclear Energy, history of atomic theory, discoveries by Rontgen, Becquerel, Rutherford, Curie, history of commercial nuclear energy

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Literally an encyclopedia

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Britannica Money

Discover all you need to know about retirement, investing, and household finance, without the jargon or agenda. Get reliable guidance, insight, and easy-to-understand explanations, written, edited, and verified to Britannica's exacting standards.

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Explore the fact-checked online encyclopedia from Encyclopaedia Britannica with hundreds of thousands of objective articles, biographies, videos, and images from experts.

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An alphabetical listing; biographies

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Lived 1845 - 1923.
The German physicist, Wilhelm Conrad Röntgen was the first person to systematically produce and detect electromagnetic radiation in a wavelength range today known as x-rays or Röntgen rays.

His discovery of x-rays was a great revolution in the fields of physics and medicine and electrified the general public. It also earned him the Rumford Medal of the Royal Society of London in 1896 and the first Nobel Prize in Physics in 1901. He is also known for his discoveries in mechanics, heat, and electricity.

Early Life and Career:

Röntgen was born on March 27, 1845, at Lennep in the Lower Rhine Province of Germany. He was the only child of a merchant and cloth manufacturer. Röntgen was brought up in Netherlands after he and his family moved to Apeldoorn in 1848. Here he first received his early education at the Institute of Martinus Herman van Doorn, a boarding school and in 1861 attended the Utrecht Technical School. Unfortunately in 1863 he was expelled unfairly from his school after being accused of a prank another student had committed. Even though Röntgen did not seem to be especially gifted in his schoolwork, he was good at building mechanical objects, a talent that enabled him to build many of his own experimental devices in his later life.

He then entered the University of Utrecht in 1865 to study physics without having the necessary credentials required for a regular student. In 1869, he earned a Ph.D. in mechanical engineering from the University of Zurich. Here he attended lectures by the noted physicist Rudolf Julius Emmanuel Clausius and also worked in the laboratory of Kundt. As soon as he completed his graduation he was appointed assistant to Kundt and went with him to Würzburg in the same year, and three years later to Strasbourg.

In 1874 he was appointed as a lecturer at Strasbourg University and in 1875 served as a professor in the Academy of Agriculture at Hohenheim in Württemberg. In 1876 he returned to Strasbourg as Professor of Physics. Three years later he accepted the invitation to the Chair of Physics in the University of Giessen. In 1888, he obtained the same position at the University of Würzburg, and in 1900 at the University of Munich. Even though he accepted an appointment at Columbia University in New York City but due to the occurrence of World War I, Röntgen changed his plans and remained in Munich for the rest of his career.

Discovery of X-rays:

For decades, he had been studying the effects of electrical charge on the response and appearance of vacuum tubes. The science of electricity was still relatively new, and there remained much to understand. His set-ups used relatively simple components by today's standards.

He conducted a series of experiments in 1895 in which he connected a type of vacuum tube (visualize a light bulb on steroids) called a Hittorf-Crookes tube to an early and very powerful electrostatic charge generator known as a Ruhmkorff coil, similar to what sparks a car motor to start. He was trying to reproduce a fluorescent effect observed with another type of vacuum tube called a Lenard tube. The filament inside produced a stream of electrons which was well-known, called a cathode ray. To his surprise, this produced fluorescence on a screen coated with a compound called barium platinocyanide, several feet away. This suggested to him that a hitherto unknown, and entirely invisible, effect was being produced. We know now that the cathode ray had excited the atoms of the aluminum to produce X-rays, which in turn excited the atoms of the barium (an element which fluoresces readily).

He also discovered that when his hand passed between the electrically charged vacuum tube and the barium platinocyanide coated screen, he saw his bones. He reproduced this phenomenon with his wife, causing horror.

After secretly confirming his findings, he published an article titled, "On A New Kind Of Rays" (Über eine neue Art von Strahlen) in 1896. This revelation and its nearly immediate application to all sorts of medical imaging earned him an honorary medical degree. He earned the Rumford Medal of the Royal Society of London in 1896 and his Nobel Prize was awarded in 1901.

Death:

Röntgen died at Munich on February 10, 1923, from carcinoma of the intestine.

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Lived 1845 - 1923. The German physicist, Wilhelm Conrad Röntgen was the first person to systematically produce and detect electromagnetic radiation in a wavelength range today known as x-rays or Röntgen rays. His discovery of x-rays was a great revolution in the fields of physics and medicine and electrified the

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Nobel Prize

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Nobelprize.org, The Official Web Site of the Nobel Prize

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Biography

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Henri Becquerel: Henri Becquerel, French physicist who discovered radioactivity through his investigations of uranium and other substances. In 1903 he shared the Nobel Prize for Physics with Pierre and Marie Curie. He was a member of a scientific family extending through several generations, the most notable being

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Nobel Prize

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Nobelprize.org, The Official Web Site of the Nobel Prize

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New York Times account

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"The story is so rich," Dr. Norris enthused. "There's layer upon layer of good stuff, interesting characters."

Still, more than six decades after the project's start, the Manhattan side of the atom bomb story seems to be a well-preserved secret.

Dr. Norris recently visited Manhattan at the request of The New York Times for a daylong tour of the Manhattan Project's roots. Only one site he visited displayed a public sign noting its role in the epochal events. And most people who encountered his entourage, which included a photographer and videographer, knew little or nothing of the atomic labors in Manhattan.

"That's amazing," Alexandra Ghitelman said after learning that the buildings she had just passed on inline skates once held tons of uranium destined for atomic weapons. "That's unbelievable."

While shock tended to be the main reaction, some people hinted at feelings of pride. More than one person said they knew someone who had worked on the secret project, which formally got under way in August 1942 and three years later culminated in the atomic bombing of Japan. In all, it employed more than 130,000 people.

Dr. Norris is also the author of "Racing for the Bomb" (Steerforth, 2002), a biography of Gen. Leslie R. Groves, the project's military leader. As his protagonist had done during the war, Dr. Norris works in Washington. At the Natural Resources Defense Council, he studies and writes about the nation's atomic facilities.

Dr. Norris began his day of exploration by taking the train to New York from Washington, coming into Pennsylvania Station just as General Groves had done dozens of times during the war to visit project sites.

"Groves didn't want the job," Dr. Norris remarked outside the station. "But his foot hit the accelerator and he didn't let up for 1,000 days."

For tour assistance, Dr. Norris brought along his own books as well as printouts from "The Traveler's Guide to Nuclear Weapons," a CD by James M. Maroncelli and Timothy L. Karpin that features little-known history of the nation's atom endeavors.

We headed north to the childhood home of J. Robert Oppenheimer, the eccentric genius whom General Groves hired to run the project's scientific side as well as its sprawling New Mexico laboratory. Last year, a biography of Oppenheimer, "American Prometheus" (Knopf, 2005), won the Pulitzer Prize.

"One of the most famous scientists of the 20th century," Dr. Norris noted, got his start "walking these streets" and attending the nearby Ethical Culture School.

Oppenheimer and his parents lived at 155 Riverside Drive, an elegant apartment building at West 88th Street. The superintendent, Joe Gugulski, said the family lived on the 11th floor, overlooking the Hudson River.

"One of my tenants read the book," Mr. Gugulski told us. "So I looked it up." To his knowledge, Mr. Gugulski added, no other atomic tourists had visited the building.

The Oppenheimers decorated their apartment with original artwork by Picasso, Rembrandt, Renoir, Van Gogh and Cézanne, according to "American Prometheus." His mother encouraged young Robert to paint.

By the late 1930s and early 1940s, blocks away at Columbia University, scientists were laboring to split the atom and release its titanic energies. We made our way across campus - with difficulty because of protests over the visit of President Mahmoud Ahmadinejad of Iran, which is widely suspected of harboring its own bomb program.

Dr. Norris noted that the Manhattan Project led to "many of our problems today."

The Pupin Physics Laboratories housed the early atom experiments, Dr. Norris said. But the tall building, topped by observatory domes, has no plaque in its foyer describing its nuclear ties.

Passing students and pedestrians answered "no" and "kind of" when asked if they knew of the atom breakthroughs at Pupin Hall. Dr. Norris said the Manhattan Project, at its peak, employed 700 people at Columbia. At one point, the football team was recruited to move tons of uranium. That work, he said, eventually led to the world's first nuclear reactor.

After lunch, we headed to West 20th Street just off the West Side Highway. The block, on the fringe of Chelsea, bristled with new galleries, and Kingdom Hall of Jehovah's Witnesses. On its north side, three tall buildings once made up the Baker and Williams Warehouses, which held tons of uranium.

Two women taking a cigarette break said they had no idea of their building's atomic past. "It's horrible," said one.

Dr. Norris's "Traveler's Guide" fact sheet said the federal government in the late 1980s and early 1990s cleaned the buildings of residual uranium. Workers removed more than a dozen drums of radioactive waste, according to the Department of Energy in Washington. "Radiological surveys show that the site now meets applicable requirements for unrestricted use," a federal document said in 1995.

We moved to Manhattan's southern tip and worked our way up Broadway along the route known as the Canyon of Heroes, the scene of many ticker-tape parades amid the skyscrapers.

At 25 Broadway, we visited a minor but important site - the Cunard Building. Edgar Sengier, a Belgian with an office here, had his company mine about 1,200 tons of high-grade uranium ore and store it on Staten Island in the shadow of the Bayonne Bridge. Though a civilian, he knew of the atomic possibilities and feared the invading Germans might confiscate his mines.

Dr. Norris said General Groves, on his first day in charge, sent an assistant to buy all that uranium for a dollar a pound - or $2.5 million. "The Manhattan Project was off to a flying start," he said, adding that the Belgian entrepreneur in time supplied two-thirds of all the project's uranium.

We walked past St. Paul's Chapel and proceeded to the soaring grandeur of the Woolworth Building, once the world's tallest, at 233 Broadway.

A major site, it housed a front company that devised one of the project's main ways of concentrating uranium's rare isotope - a secret of bomb making. On the 11th, 12th and 14th floors, the company drew on the nation's scientific best and brightest, including teams from Columbia.

Dr. Norris said the front company's 3,700 employees included Klaus Fuchs, a Soviet spy. "He was a substantial physicist in his own right," Dr. Norris said. "He contributed to the American atom bomb, the Soviet atom bomb and the British atom bomb."

So how did the Manhattan Project get its name, and why was Manhattan chosen as its first headquarters?

Dr. Norris said the answer lay at our next stop, 270 Broadway. There, at Chambers Street, on the southwest corner, we found a nondescript building overlooking City Hall Park.

It was here, Dr. Norris said, that the Army Corps of Engineers had its North Atlantic Division, which built ports and airfields. When the Corps got the responsibility of making the atom bomb, it put the headquarters in the same building, on the 18th floor.

"That way he didn't need to reinvent the wheel," Dr. Norris said of General Groves. "He used what he had at his fingertips - the entire Corps of Engineers infrastructure."

Dr. Norris added that the Corps at that time included "extraordinary people, the best and brightest of West Point."

In time, the office at 270 Broadway ran not only atom research and materials acquisition but also the building of whole nuclear cities in Tennessee, New Mexico and Washington State.

The first proposed name for the project, Dr. Norris said, was the Laboratory for the Development of Substitute Materials. But General Groves feared that would draw undo attention.

Instead, General Groves called for the bureaucratically dull approach of adopting the standard Corps procedure for naming new regional organizations. That method simply noted the unit's geographical area, as in the Pittsburgh Engineer District.

So the top-secret endeavor to build the atom bomb got the most boring of cover names: the Manhattan Engineer District, in time shortened to the Manhattan Project. Unlike other Corps districts, however, it had no territorial limits. "He was nuts about not attracting attention," Dr. Norris said.

Manhattan's role shrank as secretive outposts for the endeavor sprouted across the country and quickly grew into major enterprises. By the late summer of 1943, little more than a year after its establishment, the headquarters of the Manhattan Project moved to Oak Ridge, Tenn.

Despite this dispersal, Dr. Norris said, scientists and businesses in Manhattan, including The New York Times, continued to aid the atomic project.

In April 1945, General Groves traveled to the newspaper's offices on West 43rd Street. He asked that a science writer, William L. Laurence, be allowed to go on leave to report on a major wartime story involving science.

As early as 1940, before wartime secrecy, Mr. Laurence had reported on the atomic breakthroughs at Pupin Hall.

Now, Dr. Norris said, Mr. Laurence went to work for the Manhattan Project and became the only reporter to witness the Trinity test in the New Mexican desert in July 1945, and, shortly thereafter, the nuclear bombing of Japan.

The atomic age, Mr. Laurence wrote in the first article of a series, began in the New Mexico desert before dawn in a burst of flame that illuminated "earth and sky for a brief span that seemed eternal."

In Manhattan, the one location that has memorialized its atomic connection had nothing to do with making or witnessing the bomb, but rather with managing to survive its fury.

The spot is on Riverside Drive between 105th and 106th Streets. There, in a residential neighborhood, in front of the New York Buddhist Church, is a tall statue of a Japanese Buddhist monk, Shinran Shonin, who lived in the 12th and 13th centuries. In peasant hat and sandals, holding a wooden staff, the saint peers down on the sidewalk.

The statue survived the atomic bombing of Hiroshima, standing a little more than a mile from ground zero. It was brought to New York in 1955. The plaque calls the statue "a testimonial to the atomic bomb devastation and a symbol of lasting hope for world peace."

The statue stands a few blocks from Columbia University, where much of the bomb program began.

"I wonder how many New Yorkers know about it," Dr. Norris said of the statue, "and know the history."

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Why They Called It the Manhattan Project

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"The story is so rich," Dr. Norris enthused. "There's layer upon layer of good stuff, interesting characters." Still, more than six decades after the project's start, the Manhattan side of the atom bomb story seems to be a well-preserved secret.

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Timeline

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THE FIRST ATOMIC FILE: An Eyewitness Account Revealed by Some of the Participants and Narratively Recorded

by Corbin Allardice and Edward R. Trapnell
The U.S. Atomic Energy Commission
Washington, D.C.
November 1949

On December 2, 1942, man first initiated a self-sustaining nuclear chain reaction, and controlled it.

Beneath the West Stands of Stagg Field, Chicago, late in the afternoon of that day, a small group of scientist witnessed the advent of a new era in science. History was made in what had been a squash-rackets court.

Precisely at 3:25 P.M., Chicago time, scientist George Weil withdrew the cadmium-plated control rod and by this action man unleashed and controlled the energy of the atom.

As those who witnessed the experiment became aware of what had happened, smiles spread over their faces and a quiet ripple of applause could be heard. It was a tribute to Enrico Fermi, Nobel prizewinner, to whom, more than to any other person, the success of the experiment was due.

Fermi, born in Rome, Italy, on September 29, 1901, had been working with uranium for many years. . . . Awarded the Nobel prize in 1938, he and his family went to Sweden to receive the prize. The Italian Fascist press severely criticized him for not wearing a Fascist uniform and failing to give the Fascist salute when he received the award. The Fermis never returned to Italy.

From Sweden, having taken most of his personal possessions with him Fermi proceeded to London and thence to America where he remained {until his death in 1954}.

The modern Italian explorer of the unknown was in Chicago that cold December day in 1942. An outsider looking into the squash court where Fermi was working would have been greeted by a strange sight. In the center of the 30 by 60-foot room, shrouded on all but one side by a gray balloon-cloth envelope, was a pile of black bricks and wooden timbers, square at the bottom and a flattened sphere on top. Up to half of its height construction of this crude-appearing but complex pile (the name which has since been applied to all such devices) the standing joke among the scientists working on it was: "If people could see what we're doing with a million and a half of their dollar, they'd think we are crazy. If they knew why we were doing it, they'd be sure we are."

In relation to the atomic bomb program, of which the Chicago pile experiment was a key part, the successful result, reported on December 2, formed on more piece for the jigsaw puzzle which was atomic energy. Confirmation of the chain reactor studies was an inspiration to the leaders of the bomb project, and reassuring at the same time because the Army's Manhattan Engineer District had move ahead on many fronts. Contract negotiations were under way to build production-scale nuclear chain reactors, land had been acquired at Oak Ridge, Tennessee, and millions of dollars had been obligated.

Three years before the December 2 experiment it had been discovered that when an atom of uranium was bombarded by neutrons, and uranium atom sometimes was split, or fissioned. Later it had been found that when an atom of uranium fissioned, additional neutrons were emitted and became available for further reaction with other uranium atoms. These facts implied the possibility of a chain reaction, similar in certain respects to the reaction which is the source of the sun's energy. The facts further indicated that if a sufficient quantity of uranium could be brought together under the proper conditions, a self- sustaining chain reaction under given conditions is known as the critical mass, or more commonly, the "critical size" of the particular pile. . . .

Further impetus to the work on a uranium reactor was given by the discovery of plutonium at the Radiation Laboratory, Berkeley, California, in March, 1940. This element, unknown in nature, was formed by uranium 238 capturing a neutron, and thence undergoing two successive changes in atomic structure with the emission of beta particles. Plutonium, it was believed, would undergo fission as did the rare isotope of uranium, U235.

Meanwhile at Columbia Fermi and Walter Zinn and their associates were working to determine operationally possible designs of a uranium chain reactor. Among other things,they had to find a suitable moderating material slow down the neutrons traveling at relatively fast velocities. In July, 1941, experiments with uranium were started to obtain measurements of the reproduction factor (called "k"), which was the key to the problem of a chain reaction. If this factor could be made sufficiently greater than 1, a chain reaction could be made to take place in a mass of material of practical dimensions. If it were less than 1, no chain reaction could occur.

Since impurities in the uranium and in the moderator would capture neutrons and make them unavailable for further reactions, and since neutrons would escape from the pile without encountering uranium 235 atoms, it was not known whether a value for "k" greater than unity could ever be obtained.

Fortunate it was that the obtaining of a reproduction factor greater than 1 was a complex and difficult problem. If Hitler's scientists had discovered the secret of controlling the neutrons and had obtained a working value of "k," they would have been well on the way toward producing an atomic bomb for the Nazis.

One of the first things that had to be determined was how best to place the uranium in the reactor. Fermi and Leo Szilard suggested placing the uranium in a matrix of the moderating material, thus forming a cubical lattice of uranium. This placement appeared to offer the best opportunity for a neutron to encounter a uranium atom. Of all the materials which possessed the proper moderating qualities, graphite was the only one which could be obtained in sufficient quantity of the desired degree of purity.

The study of graphite-uranium lattice reactors was started at Columbia in July, 1941, but after reorganization of the uranium project in December, 1941, Arthur H. Compton was placed in charge of this phase of the work, under the Office of Scientific Research and Development, and it was decided that the chain reactor program should be concentrated at the University of Chicago. Consequently early in the 1942 the Columbia and Princeton groups were transferred to Chicago, where the Metallurgical Laboratory was established. . . .

At Chicago, the work on sub-critical size piles was continued. By July, 1942, the measurements obtained from these experimental piles had gone far enough to permit a choice of design for a test pile of critical size. At that time, the dies for the pressing of the uranium oxides were designed by Zinn and ordered made. It was a fateful step, since the entire construction of the pile depended upon the shape and size of uranium pieces.

It was necessary to use uranium oxides because metallic uranium of the desired degree of purity did not exist. Although several manufacturers were attempting to produce the uranium metal, it was no until November that any appreciable amount was available. . . .

Although the dies for the pressing of the uranium oxides were designed in July, additional measurements were necessary to obtain information about controlling the reaction, to revise estimates as to the final critical size of the pile, and to develop other data. Thirty experimental sub-critical piles were constructed before the final pile was completed.

Meantime, in Washington, Vannevar Bush, Director of the Office of Scientific Research and Development, had recommended to President Roosevelt that a special Army Engineer organization be established to take full responsibility for the development of the atomic bomb, During the summer, the Manhattan Engineer District was created, and in September, 1942, Major General L.R. Groves assumed command.

Construction of the main pile at Chicago started in November. The project gained momentum, with machining of the graphite blocks, pressing of the uranium oxide pellets, and the design of instruments. Fermi's two "construction" crews, one under Zinn and the other under Herbert L. Anderson, worked almost around the clock, V.C. Wilson headed the instrument work.

Original estimates as to the critical size of the pile were pessimistic. As a further precaution, it was decided to enclose the pile in a balloon-cloth bag which could be evacuated to remove the neutron-capturing air. . . .

The bag was hung with one side left open; in the center of the floor a circular layer of graphite bricks was placed. This and each succeeding layer of the pile was braced by a wooden frame. Alternate layers contained the uranium. By this layer-on-layer construction a roughly spherical pile of uranium and graphite was formed.

Facilities for the machining of graphite bricks were installed in the West Stands. Week after week this shop turned out graphite bricks. This work was done under the direction of Zinn's group, by skilled mechanics led by millwright August Knuth. In October, Anderson and his associates joined Zinn's men.

Describing this phase of the work, Albert Wattenberg, one of Zinn's group, said: "We found out how coal miners feel. After eight hours of machining graphite, we looked as if we were made up for a minstrel. One shower would only remove the dust in the pores of our skin would start oozing. Walking around the room where we cut the graphite was like walking on a dance floor. Graphite is a dry lubricant, you know, and the cement floor covered with graphite dust was slippery."

Before the structure was half completed; measurements indicated that the critical size at which the pile would become self-sustaining was somewhat less than had been anticipated in the design.

Day after day the pile grew toward its final shape. And as the size of the pile increased, so did the nervous tension of the men working on it. Logically and scientifically they knew this pile would become self-sustaining. It had to. All the measurements indicated that it would. But still the demonstration had to be made. As they eagerly awaited moment drew nearer, the scientist gave greater and greater attention to details, the accuracy of measurements, and exactness of their construction work. . . .

At Chicago during the early afternoon of December 1, tests indicated that critical size was rapidly being approached. At 4PM Zinn's group was relieved by the men working under Anderson. Shortly afterwards the last layer of graphite and uranium bricks was placed on the pile. Zinn, who remained, and Anderson made several measurements of the activity within the pile would become self-sustaining. Both had agreed, however, that should measurements indicate the reaction would become self-sustaining until Fermi and the rest of the group could be present. Consequently, the control rods were locked and further work was postponed until the following day.

That night the word was passed to the men who had worked on the pile that the trial run was due the next morning.

About 8:30 on the morning of Wednesday, December 2, the group began to assemble in the squash court.

At the north end of the squash court was a balcony about ten feet above the floor of the court. Fermi, Zinn, Anderson, and Compton were grouped around instruments at the east end of the balcony. The remainder of the observers crowded the little balcony. R.G. Noble, one of the young scientists who worked on the pile, put it this way: "The control cabinet was surrounded by the "big wheels"l; the "little wheels' had to stand back."

On the floor of the squash court, just beneath the balcony, stood George Weil, whose duty it was to handle the final control rod. In the pile were three sets of control rods. One set was automatic and could be controlled from the balcony. Another was an emergency safety rod. Attached to one end of this rod was a rope running through the pile and weighted heavily on the opposite end. The rod was withdrawn from the pile and tied by another rope to the balcony. Hilberry was ready to cut this rope with an ax should sometimes unexpected happen, or in case the automatic safety held the reaction in check until withdrawn the proper distance.

Since this demonstration was new and different from anything ever done before, complete reliance was not placed on mechanically operated control rods. Therefore a "liquid control squad," composed of Harold Lichtenberger, W. Nyter, and A.C. Graces, stood on a platform above the pile. They were prepared to flood the pile with cadmium-salt solution in case of mechanical failure of the control rods.

Each group rehearsed its part of the experiment.

At 9:45 Fermi ordered the electrically operated control rods withdrawn. The man at the controls threw the switch to withdraw them. A small motor whined. All eyes watch the lights which indicated the rod's position.

But quickly the balcony group turned to watch the counters, whose clicking stepped up after the rods were out. The indicators of these counters resembled the face of a clock, with "hands" to indicate neutron activity within the pile.

Shortly after ten o'clock, Fermi ordered the emergency rod, called "Zip," pulled out and tied.

"Zip Out," said Fermi. Zinn withdrew "Zip" by hand and tied it to the balcony rail. Weil stood ready by the "vernier" control rod which was marked to show the number feet and inches which remained within the pile.

At 10:37 Fermi, without taking his eyes off the instruments, said quietly: "Pull it to 13 feet, George." The counters clicked faster. The graph pen moved up. All the instruments were studied, and computations were made.

"This is not it," said Fermi. "The trace will go to this point and level off." He indicated a spot on the graph. In a few minutes the pen came to the indicated point and did not go above that point. Seven minutes later Fermi ordered the rod out another foot.

Again the counters stepped up their clicking, the graph pen edged upwards. But the clicking was irregular. Soon it leveled off, as did the thin line of the pen. The pile was not self-sustaining-- yet.

At 11 o'clock, the rod came out another six inches; the result was the same: an increase in rate, followed by the leveling off.

Fifteen minutes later, the rod was farther withdrawn and at 11:25 was moved again. Each time the counters speeded up, the pen climbed a few points. Fermi predicted correctly every movement of the indicators. He knew the time was near. He wanted to check everything again. The automatic control rod was reinserted without waiting for its automatic feature to operate. The graph line took a drop, the counters slowed abruptly.

At 11:35, the automatic safety rod was withdrawn and set. The control rod was adjusted and "Zip" was withdrawn. Up went the counters, clicking, clicking, faster and faster. It was the clickety-click of a fast train over the rails. The graph pen started to climb. Tensely, the little group watched and waited, entranced by the climbing needle.

Whrrrump! As if by a thunderclap, the spell was broken. Every man froze-- then breathed a sigh of relief when he realized the automatic rod had slammed home. The safety point at which the rod operated automatically had been set too low.

"I'm hungry," said Fermi. "Let's go to lunch."

Perhaps, like a great coach, Fermi knew when his men needed a "break." It was strange "between halves" respite. They got no pep talk. They talked about everything else but the "game." The redoubtable Fermi, who never says much, had even less to say. But he appeared supremely confident. His "team" was back on the squash court at 2:00PM. Twenty minutes later, the automatic rod was reset and Weil stood ready at the control rod.

"All right, George," called Fermi, and Weil moved the rod to a predetermined point. The spectators resumed their watching and waiting, watching the counters spin, watching the graph, waiting for the settling down, and computing the rate of rise of reaction from the indicators.

At 2:50 the control rod came out another foot. The counters nearly jammed, the pen headed off the graph paper. But this was not it. Counting ratios and the graphs scale had to be changed.

"Move it six inches," said Fermi at 3:20. Again the change-- but again the leveling off. Five minutes later, Fermi called: "Pull it out another foot."

Weil withdrew the rod.

"This is going to do it, "Fermi said to Compton, standing at his side. "Now it will become self-sustaining. The trace will climb and continue to climb. It will not level off."

Fermi computed the rate of rise of the neutron counts over a minute period. He silently, grim-faced, ran through some calculations on his slide rule.

In about a minute he again computed the rate of rise. If the rate was constant and remained so, he would know the reaction was self-sustaining. His fingers operated the slide rule with lightning speed. Characteristically, he turned the rule over and jotted down some figures on its ivory back.

Three minutes later he again computed the rate of rise in neutron count. The group on the balcony had by now crowded in to get an eye on the instruments, those behind craning their necks to be sure they would know the very instant history was made. In the background could be heard William Overbeck calling out the neutron count over an annunciator system. Leona Marshall (the only girl present), Anderson, and William Sturm were recording the readings from the instruments. By this time the click of the counters was too fast for the human ear. The clickety-click was now a steady brrrrr. Fermi, unmoved, unruffled, continued his computations.

"I couldn't see the instruments," said Weil. "I had to watch Fermi every second, waiting for orders. His face was motionless. His eyes darted from one dial to another. His expression was so calm it was hard. But suddenly, his whole face broke into a broad smile."

Fermi closed his slide rule---

"The reaction is self-sustaining," he announced quietly, happily. "The curve is exponential."

The group tensely watched for twenty-eight minutes while the world's first nuclear chain reactor operated.

The upward movement of the pen was leaving a straight line. There was no change to indicate a leveling off. This was it.

"O.K., "Zip' in," called Fermi to Zinn, who controlled that rod. The time was 3:53PM. Abruptly, the counters slowed down, the pen slid down across the paper. It was all over.

Man had initiated a self-sustaining nuclear reaction-- and then stopped it. He had released the energy of the atom's nucleus and controlled that energy.

Right after Fermi ordered the reaction stopped, the Hungarian born theoretical physicist Eugene Wigner presented him with a bottle of Chianti wine. All through the experiment Wigner had kept this wine hidden behind his back.

Fermi uncorked the wine bottle and sent out for paper cups so all could drink. He poured a little wine in all the cups, and silently, solemnly, without toasts, the scientists raised the cups to their lips- the Canadian Zinn, Compton, Anderson, Hilberry, and a score of others. They drank to success- and to hope they were the first to succeed.

A small crew was left to straighten up, lock controls, and check all apparatus. As the group filed from the West Stands, one of the guards asked Zinn: "What's going on, Doctor, something happen in there?"

The guard did not hear the message which Arthur Compton was giving James B. Conant at Harvard, by long distance telephone. Their code was not prearranged.

"The Italian navigator has landed in the New World," said Compton.

"How were the natives?" asked Conant.

"Very friendly."

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by Corbin Allardice and Edward R. Trapnell The U.S. Atomic Energy Commission Washington, D.C. November 1949 On December 2, 1942, man first initiated a self-sustaining nuclear chain reaction, and controlled it. Beneath the West Stands of Stagg Field, Chicago, late in the afternoon of that day, a small group of scientist witnessed the advent of a new era in science.

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Nuclear Chemistry; The first chain reaction

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Nuclear Chemistry; The first chain reaction

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A chemistry perspective

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Help Spread the Word! The LibreTexts Project is the now the highest ranked and most visited online OER textbook project thanks to you.

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The science behind the atom bomb

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The immense destructive power of atomic weapons derives from a sudden release of energy produced by splitting the nuclei of the fissile elements making up the bombs' core. The U.S. developed two types of atomic bombs during the Second World War. The first, Little Boy, was a gun-type weapon with a uranium core. Little Boy was dropped on Hiroshima. The second weapon, dropped on Nagasaki, was called Fat Man and was an implosion-type device with a plutonium core.

Fission

The isotopes uranium-235 and plutonium-239 were selected by the atomic scientists because they readily undergo fission. Fission occurs when a neutron strikes the nucleus of either isotope, splitting the nucleus into fragments and releasing a tremendous amount of energy. The fission process becomes self-sustaining as neutrons produced by the splitting of atom strike nearby nuclei and produce more fission. This is known as a chain reaction and is what causes an atomic explosion.

When a uranium-235 atom absorbs a neutron and fissions into two new atoms, it releases three new neutrons and some binding energy. Two neutrons do not continue the reaction because they are lost or absorbed by a uranium-238 atom. However, one neutron does collide with an atom of uranium-235, which then fissions and releases two neutrons and some binding energy. Both of those neutrons collide with uranium-235 atoms, each of which fission and release between one and three neutrons, and so on. This causes a nuclear chain reaction. For more on this topic, see Nuclear Fission.

Criticality

In order to detonate an atomic weapon, you need a critical mass of fissionable material. This means you need enough U-235 or Pu-239 to ensure that neutrons released by fission will strike another nucleus, thus producing a chain reaction. The more fissionable material you have, the greater the odds that such an event will occur. Critical mass is defined as the amount of material at which a neutron produced by a fission process will, on average, create another fission event.

The Difference Between the Bombs

Little Boy and Fat Man utilized different elements and completely separate methods of construction in order to function as nuclear weapons. Little Boy detonated due to a fission chain reaction involving the isotope U-235 of uranium, while Fat Man used plutonium's Pu-239 form.

Little Boy

Little Boy was powered by the uranium isotope U-235 in a process that didn't come easily to the many Manhattan Project scientists working on the uranium extraction and enrichment process. Most uranium found naturally in the world exists as uranium-238, leaving only 0.7% of naturally existing uranium as the U-235 isotope. When a neutron bombards U-238, the isotope often captures the neutron to become U-239, failing to fission, and thus failing to instigate a chain reaction that would detonate a bomb. The first challenge of the project was thus to determine the most efficient way to separate and purify uranium-235 from the overly-abundant uranium-238 - standard methods of separation could not be used due to the strong chemical similarity between the two isotopes. In order to avoid wasting time on one new method that could later prove insufficient to produce enough U-235 to allow the atomic bomb to reach critical mass, General Leslie Groves consulted with lead scientists of the project and agreed to investigate simultaneously four separate methods of separating and purifying the uranium-235: gaseous diffusion, centrifuge, electromagnetic separation and liquid thermal diffusion.

Once enough U-235 was obtained to power the bomb, Little Boy was constructed using a gun-type design that fired one amount of U-235 at another to combine the two masses. This combination created a critical mass that set off a fission chain reaction to eventually detonate the bomb. The two masses of U-235 had to combine with one another quickly enough to avoid the spontaneous fission of the atoms, which would cause the bomb to fizzle, and thus fail to explode.

Fat Man

Powered by plutonium, Fat Man could not use the same gun-type design that allowed Little Boy to explode effectively - the form of plutonium collected from the nuclear reactors at Hanford, WA for the bomb would not allow for this strategy. The Hanford plutonium emerged from the reactors less pure than the initial plutonium extracted from Ernest O. Lawrence's Berkeley Lab, instead containing traces of isotope plutonium-240, as opposed to the desired plutonium-239. Plutonium-240's higher fission rate would cause the atoms to undergo spontaneous fission before the gun-type design could bring two masses of plutonium together, which would lower the energy involved in the actual detonation of the bomb.

Thus, a new design was required. Physicist Seth Neddermeyer at Los Alamos constructed a design for the plutonium bomb that used conventional explosives around a central plutonium mass to quickly squeeze and consolidate the plutonium, increasing the pressure and density of the substance. An increased density allowed the plutonium to reach its critical mass, firing neutrons and allowing the fission chain reaction to proceed. To detonate the bomb, the explosives were ignited, releasing a shock wave that compressed the inner plutonium and led to its explosion.

Atom: building blocks of matter; made up of a small, dense nucleus surrounded by a cloud of electrons (negatively-charged particles)

Nucleus: makes up the center of the atom; consists of a number of positively-charged protons and a neutral (no charge) neutrons. An atom is classified by the number of protons and neutrons in its nucleus. The number of protons determines which chemical element the atom is (e.g. uranium), and the number of neutrons determines which isotope of that element the atom is (e.g. uranium-235).

Isotope: Isotopes of an element possess the same number of protons in their nuclei but have different numbers of neutrons.

Fission: the process by which an atom's nucleus is split into smaller particles; results in the release of neutrons and lots of energy.

E=mc²: Equation made famous by Albert Einstein. Explains how a tiny amount of matter contains a tremendous amount of energy.

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The immense destructive power of atomic weapons derives from a sudden release of energy produced by splitting the nuclei of the fissile elements making up the bombs' core. The U.S. developed two types of atomic bombs during the Second World War. The first, Little Boy, was a gun-type weapon with a uranium core.

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Background and the process

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On this page:

Uranium Isotopes

When uranium is mined, it consists of approximately 99.3% uranium-238 (U ²³⁸), 0.7% uranium-235 (U ²³⁵), and < 0.01% uranium-234 (U ²³⁴). These are the different uranium isotopes. Isotopes of uranium contain 92 protons in the atom's center or nucleus. (The number of protons in the nucleus is what makes the atoms "uranium.") The U ²³⁸ atoms contain 146 neutrons, the U ²³⁵ atoms contain 143 neutrons, and the U ²³⁴ atoms contain only 142 neutrons. The total number of protons plus neutrons gives the atomic mass of each isotope - that is 238, 235, or 234, respectively. On an atomic level, the size and weight of these isotopes are slightly different. This implies that with the right equipment and under the right conditions, the isotopes can be separated.

Enriching Uranium

The nuclear fuel used in a nuclear reactor needs to have a higher concentration of the U ²³⁵ isotope than that which exists in natural uranium ore. U ²³⁵ when concentrated (or "enriched") is fissionable in light-water reactors (the most common reactor design in the USA). During fission, the nucleus of the atom splits apart producing both heat and extra neutrons. Under controlled conditions, these extra neutrons can cause additional, nearby atoms to fission and a nuclear reaction can be sustained. The heat energy released, by the controlled nuclear reaction within the nuclear reactor, can be harnessed to produce electricity. Commercially, the U ²³⁵ isotope is enriched to 3 to 5% (from the natural state of 0.7%) and is then further processed to create nuclear fuel.

At the conversion plant, uranium oxide is converted to the chemical form of uranium hexafluoride (UF ₆) to be usable in an enrichment facility. UF ₆ is used for a couple reasons; 1) The element fluorine has only one naturally-occurring isotope which is a benefit during the enrichment process (e.g. while separating U ²³⁵ from U ²³⁸ the fluorine does not contribute to the weight difference), and 2) UF ₆ exists as a gas at a suitable operating temperature.

The two primary hazards at enrichment facilities include chemical hazards that could be created from a UF ₆ release and criticality hazards associated with enriched uranium.

There are several enrichment processes utilized worldwide. They are:

Gaseous Diffusion

Gaseous diffusion was the first commercial process used in the United States to enrich uranium. These facilities utilized massive amounts of electricity and as the centrifuge technology matured the existing gaseous diffusion plants became obsolete. Worldwide they have all been replaced by second-generation technology, which requires far less electric power to produce equivalent amounts of separated uranium. These facilities are now considered obsolete.

Process: In a gaseous diffusion enrichment plant, uranium hexafluoride (UF ₆) gas was fed into the plant's pipelines where it was pumped through special filters called barriers or porous membranes. The holes in the barriers were so small that there was barely enough room for the UF ₆ gas molecules to pass through as shown in this diagram. The isotope enrichment occurred because the lighter UF ₆ gas molecules (with the U ²³⁴ and U ²³⁵ atoms) diffused faster through the barriers than the heavier UF ₆ gas molecules containing U ²³⁸. One barrier wasn't enough though. It took many hundreds of barriers, one after the other, before the UF ₆ gas contained enough U ²³⁵ to be used in nuclear fuel. At the end of the process, the enriched UF ₆ gas was withdrawn from the pipelines and condensed back into a liquid that was then poured into containers. The UF ₆ was allowed to cool and solidify before it was transported to fuel fabrication facilities. The diagram to the right illustrates the gaseous diffusion enrichment process.

Legacy Plants: The gaseous diffusion plants that were historically operated in the United States were located in Paducah, Kentucky; Piketon, Ohio; and Oak Ridge, Tennessee. The U.S. government leased the Piketon and Paducah plants to the United States Enrichment Corporation (USEC) in March 4, 1997. Both plants enriched uranium for commercial use and were regulated by the Nuclear Regulatory Commission (NRC). Since then, both plants have been shut down. The certificates were transferred back to the U.S. Department of Energy (DOE); the agency responsible for the safe decommissioning of the plants.

While the two gaseous diffusion plants were under NRC purview, their certificates were issued in accordance with 10 CFR Part 76. The NRC maintained one or two resident inspectors on site while the facilities were in operation. Inspectors out of the regional and headquarters office also performed inspections. Documents pertaining to safety inspections conducted by the NRC can be found below. The current status of decommissioning can be obtained on the Portsmouth/Paducah Project Office page maintained by the DOE.
Paducah Portsmouth
Both the operation and decommissioning of the gaseous diffusion plant in Oak Ridge, TN was regulated by the DOE and was never under NRC purview.

Gas Centrifuge

Gas centrifuge enrichment is the current process by which commercial enrichment is being performed in the United States. UF ₆ gas is placed in a gas centrifuge cylinder and rotated at a high speed. This rotation creates a strong centrifugal force so that the heavier gas molecules (UF ₆ containing U ²³⁸ atoms) move towards the outside of the cylinder. The lighter gas molecules (containing U ²³⁵) collect closer to the center. The stream that is slightly enriched in U ²³⁵ is withdrawn and fed into the next centrifuge; the next higher stage. The slightly depleted stream (with a lower concentration of U ²³⁵) is recycled back into the next lower stage.

A gas centrifuge facility contains long lines of many rotating cylinders. These cylinders are connected in both series and parallel formations. Centrifuge machines are interconnected to form trains and cascades. At the final withdrawal point, the UF ₆ is enriched to the desired amount.

Currently, the only gas centrifuge commercial production plant is the URENCO USA (UUSA) facility licensed as Louisiana Energy Services (LES). UUSA is currently operating in Eunice, NM. Two other licenses were granted by the NRC for the construction of commercial gas centrifuge facilities. The status of these licensees are found in this chart.

Laser Separation

The laser separation technology is under development for possible use to enrich uranium. Uranium can be enriched by separating isotopes of uranium with lasers. Molecules can be excited by laser light; this is called photoexcitation. Lasers can increase the energy in the electrons of a specific isotope, changing its properties and allowing it to be separated.

In general, the enrichment process entails using three major systems, which are the laser systems, optical systems, and separation module system. Tunable lasers can be developed to deliver a highly monochromatic light (light of a single-color). The light from these lasers can photo-ionize a specific isotopic species while not affecting other isotopic species. The affected species is then chemically changed, which enables the material to be separated. The laser separation technology developed by DOE used a uranium metal alloy as its feed material, while the Separation of Isotopes by Laser Excitation (SILEX) method uses UF ₆ as the feed material.

No laser separation uranium enrichment plants are currently operating in the United States. However, on May 12, 2008, the NRC approved a license amendment submitted by General Electric - Hitachi seeking approval for research and development associated with laser enrichment to be conducted at its Global Nuclear Fuels-Americas, LLC facility in Wilmington, NC. GE Hitachi constructed a test loop and illustrated the SILEX laser isotope separation process. On September 25, 2012, NRC staff issued a construction and operating license for the facility. The current status of the facility can be found on the New Fuel Cycle Facility Licensing page.
Page Last Reviewed/Updated Wednesday, August 02, 2017

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On this page: When uranium is mined, it consists of approximately 99.3% uranium-238 (U 238), 0.7% uranium-235 (U 235), and < 0.01% uranium-234 (U 234). These are the different uranium isotopes. Isotopes of uranium contain 92 protons in the atom's center or nucleus.

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More about Plutonium

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health and environmental effects element elements periodic table chart measurement laboratory environment healthy

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Plutonium (Pu) - Chemical properties, Health and Environmental effects

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chemical properties, health and environmental effects of plutonium

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Plutonium

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Plutonium. Info paper on Pu, Over one third of the energy produced in most nuclear power plants comes from plutonium. Plutonium has occurred naturally, but except for trace quantities it is not now found in the earth's crust. There are several tonnes of plutonium in our biosphere.

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The Nobel Prize in Chemistry

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Nobel Lecture, December 11, 1911

Radium and the New Concepts in Chemistry

Some 15 years ago the radiation of uranium was discovered by Henri Becquerel, and two years later the study of this phenomenon was extended to other substances, first by me, and then by Pierre Curie and myself. This study rapidly led us to the discovery of new elements, the radiation of which, while being analogous with that of uranium, was far more intense. All the elements emitting such radiation I have termed radioactive, and the new property of matter revealed in this emission has thus received the name radioactivity. Thanks to this discovery of new, very powerful radioactive substances, particularly radium, the study of radioactivity progressed with marvellous rapidity: Discoveries followed each other in rapid succession, and it was obvious that a new science was in course of development. The Swedish Academy of Sciences was kind enough to celebrate the birth of this science by awarding the Nobel Prize for Physics to the first workers in the field, Henri Becquerel, Pierre Curie and Marie Curie (1903).

From that time onward numerous scientists devoted themselves to the study of radioactivity. Allow me to recall to you one of them who, by the certainty of his judgement, and the boldness of his hypotheses and through the many investigations carried out by him and his pupils, has succeeded not only in increasing our knowledge but also in classifying it with great clarity; he has provided a backbone for the new science, in the form of a very precise theory admirably suited to the study of the phenomena. I am happy to recall that Rutherford came to Stockholm in 1908 to receive the Nobel Prize as a well-deserved reward for his work.

Far from halting, the development of the new science has constantly continued to follow an upward course. And now, only 15 years after Becquerel's discovery, we are face to face with a whole world of new phenomena belonging to a field which, despite its close connexion with the fields of physics and chemistry, is particularly well-defined. In this field the importance of radium from, the viewpoint of general theories has been decisive. The history of the discovery and the isolation of this substance has furnished proof of my hypothesis that radioactivity is an atomic property of matter and can provide a means of seeking new elements. This hypothesis has led to present-day theories of radioactivity, according to which we can predict with certainty the existence of about 30 new elements which we cannot generally either isolate or characterize by chemical methods. We also assume that these elements undergo atomic transformations, and the most direct proof in favour of this theory is provided by the experimental fact of the formation of the chemically defined element helium starting from the chemically-defined element radium.

Viewing the subject from this angle, it can be said that the task of isolating radium is the corner-stone of the edifice of the science of radioactivity. Moreover, radium remains the most useful and powerful tool in radioactivity laboratories. I believe that it is because of these considerations that the Swedish Academy of Sciences has done me the very great honour of awarding me this year's Nobel Prize for Chemistry.

It is therefore my task to present to you radium in particular as a new chemical element, and to leave aside the description of the many radioactive phenomena which have already been described in the Nobel Lectures of H. Becquerel, P. Curie and E. Rutherford.

Before broaching the subject of this lecture, I should like to recall that the discoveries of radium and of polonium were made by Pierre Curie in collaboration with me. We are also indebted to Pierre Curie for basic research in the field of radioactivity, which has been carried out either alone, in collaboration with his pupils.

The chemical work aimed at isolating radium in the state of the pure salt, and at characterizing it as a new element, was carried out specially by me, but it is intimately connected with our common work. I thus feel that I interpret correctly the intention of the Academy of Sciences in assuming that the award of this high distinction to me is motivated by this common work and thus pays homage to the memory of Pierre Curie.

I will remind you at the outset that one of the most important properties of the radioactive elements is that of ionizing the air in their vicinity (Becquerel). When a uranium compound is placed on a metal plate A situated opposite another plate B and a difference in potential is maintained between the plates A and B, an electric current is set up between these plates; this current can be measured with accuracy under suitable conditions and will serve as a measure of the activity of the substance. The conductivity imparted to the air can be ascribed to ionization produced by the rays emitted by the uranium compounds.

In 1897, using this method of measurement, I undertook a study of the radiation of uranium compounds, and soon extended this study to other substances, with the aim of finding out whether radiation of this type occurs in other elements. I found in this way that of the other elements known, only the compounds of thorium behave like the compounds of uranium.

I was struck by the fact that the activity of uranium and thorium compounds appears to be an atomic property of the element uranium and of the element thorium. Chemical compounds and mixtures containing uranium and thorium are active in direct proportion to the amount of these metals contained in them. The activity is not destroyed by either physical changes of state or chemical transformations.

I measured the activity of a number of minerals; all of them that appear to be radioactive always contain uranium or thorium. But an unexpected fact was noted: certain minerals (pitchblende, chalcolite, autunite) had a greater activity than might be expected on the basis of their uranium or thorium content. Thus, certain pitchblendes containing 75% of uranium oxide are about four times as radioactive as this oxide. Chalcolite (crystallized phosphate of copper and uranium) is about twice as radioactive as uranium. This conflicted with views which held that no mineral should be more radioactive than metallic uranium. To explain this point I prepared synthetic chalcolite from pure products, and obtained crystals, whose activity was completely consistent with their uranium content; this activity is about half that of uranium.

I then thought that the greater activity of the natural minerals might be determined by the presence of a small quantity of a highly-radioactive material, different from uranium, thorium and the elements known at present. It also occurred to me that if this was the case I might be able to extract this substance from the mineral by the ordinary methods of chemical analysis. Pierre Curie and I at once carried out this research, hoping that the proportion of the new element might reach several per cent. In reality the proportion of the hypothetical element was far lower and it took several years to show unequivocally that pitchblende contains at least one highly-radioactive material which is a new element in the sense that chemistry attaches to the term.

We were thus led to create a new method of searching for new elements, a method based on radioactivity considered as an atomic property of matter. Each chemical separation is followed by a measurement of the activity of the products obtained, and in this way it is possible to determine how the active substance behaves from the chemical viewpoint. This method has come into general application, and is similar in some ways to spectral analysis. Because of the wide variety of radiation emitted, the method could be perfected and extended, so that it makes it possible, not only to discover radioactive materials, but also to distinguish them from each other with certainty.

It was also found in using the method being considered, that it was in fact possible to concentrate the activity by chemical methods. We found that pitchblende contains at least two radioactive materials, one of which, accompanying bismuth, has been given the name polonium, while the other, paired with barium, has been called radium.

Other radioactive elements have been discovered since: actinium (Debierne), radiothorium and mesothorium (Hahn), ionium (Boltwood), etc.

We were convinced that the materials which we had discovered were new chemical elements. This conviction was based solely on the atomic nature of radioactivity. But at first, from the chemical viewpoint, it was as if our substances had been, the one pure bismuth, and the other pure barium. It was vital to show that the radioactive property was connected with traces of elements that were neither bismuth nor barium. To do that the hypothetical elements had to be isolated. In the case of radium isolation was completely successful but required several years of unremitting effort. Radium in the pure salt form is a substance the manufacture of which has now been industrialized; for no other new radioactive substance have such positive results been obtained.

The radiferous minerals are being subjected to very keen study because the presence of radium lends them considerable value. They are identifiable either by the electrometric method, or very simply by the impression they produce on a photographic plate. The best radium mineral is the pitchblende from St. Joachimsthal (Austria) which has for a long time been processed to yield uranium salts. After extraction of the latter, the mineral leaves a residue which contains radium and polonium. We have normally used this residue as our raw material.

The first treatment consists in extracting the radiferous barium and the bismuth containing the polonium. This treatment, which was first performed in the laboratory on several kilograms of raw material (as many as 20 kg) had then to be undertaken in a factory owing to the need to process thousands of kilograms. Actually, we gradually learned from experience that the radium is contained in the raw material in the proportion of a few decigrams per ton. About 10 to 20 kg crude barium sulphate containing radium are extracted from one ton of residue. The activity of these sulphates is even then 30 to 60 times greater than that of uranium. These sulphates are purified and converted to chlorides. In the mixture of barium and radium chlorides the radium is present only in the proportion of about 3 parts per 100,000. In the radium industry in France a much lower grade mineral is most often used and the proportion indicated is far lower still. To separate the radium from the barium I have used a method of fractional crystallization of the chloride (the bromide can also be used). The radium salt, less soluble than the barium salt, becomes concentrated in the crystals. Fractionation is a lengthy, methodical operation which gradually eliminates the barium. To obtain a very pure salt I have had to perform several thousands of crystallizations. The progress of the fractionation is monitored by activity measurements.

A first proof that the element radium existed was furnished by spectral analysis. The spectrum of a chloride enriched by crystallization exhibited a new line which Demarcay attributed to the new element. As the activity became more concentrated, the new line increased in intensity and other lines appeared while the barium spectrum became at the same time less pronounced. When the purity is very high the barium spectrum is scarcely visible.

I have repeatedly determined the average atomic weight of the metal in the salt subjected to spectral analysis. The method used was the one consisting in determining the chlorine content in the form of silver chloride in a known amount of the anhydrous chloride. I have found that this method gives very good results even with quite small amounts of substance (0.1 to 0.5 g), provided a very fast balance is used to avoid the absorption of water by the alkaline-earth salt during the weighings. The atomic weight increases with the enrichment of the radium as indicated by the spectrum. The successive atomic weights obtained were: 138; 146; 174; 225; 226.45. This last value was determined in 1907 with 0.4 g of very pure radium salt. The results of a number of determinations are, 226.62; 226.31; 226.42. These have been confirmed by more recent experiments.

The preparation of pure radium salts and the determination of the atomic weight of radium have proved positively that radium is a new element and have enabled a definite position to be assigned to it. Radium is the higher homologue of barium in the family of alkaline-earth metals; it has been entered in Mendeleev's table in the corresponding column, on the row containing uranium and thorium. The radium spectrum is very precisely known. These very clear-cut results for radium have convinced chemists and justified the establishment of the new science of radioactive substances.

In chemical terms radium differs little from barium; the salts of these two elements are isomorphic, while those of radium are usually less soluble than the barium salts. It is very interesting to note that strong radioactivity of radium involves no chemical anomalies and that the chemical properties are actually those which correspond to the position in the Periodic System indicated by its atomic weight. The radioactivity of radium in solid salts is ca. 5 million times greater than that of an equal weight of uranium. Owing to this activity its salts are spontaneously luminous. I also wish to recall that radium gives rise to a continuous liberation of energy which can be measured as heat, being about 118 calories per gram of radium per hour.

Radium has been isolated in the metallic state (M. Curie and A. Debierne, 1910). The method used consisted in distilling under very pure hydrogen the amalgam of radium formed by the electrolysis of a chloride solution using a mercury cathode. One decigram only of salt was treated and consequently considerable difficulties were involved. The metal obtained melts at about 700°C, above which temperature it starts to volatilize. Is it very unstable in the air and decomposes water vigorously.

The radioactive properties of the metal are exactly the ones that can be forecast on the assumption that the radioactivity of the salts is an atomic property of the radium which is unaffected by the state of combination. It was of real importance to corroborate this point as misgivings had been voiced by those to whom the atomic hypothesis of radioactivity was still not evident.

Although radium has so far only been obtained in very small amounts, it is nevertheless true to say, in conclusion, that it is a perfectly defined and already well-studied chemical element.

Unfortunately, the same cannot be stated for polonium, for which nevertheless considerable effort has already been spent. The stumbling block here is the fact that the proportion of polonium in the mineral is about 5,000 times smaller than that of radium.

Before theoretical evidence was available from which to forecast this proportion, I had conducted several extremely laborious operations to concentrate polonium and in this way had secured products with very high activity without being able to arrive at definite results as in the case of radium. The difficulty is heightened by the fact that polonium disintegrates spontaneously, disappearing by half in a period of 140 days. We now know that radium has not an infinite life either, but the rate of disappearance is far less (it disappears by half in 2,000 years). With our facilities we can scarcely hope to determine the atomic weight of polonium because theory foresees that a rich mineral can contain only a few hundredths of a milligram per ton, but we can hope to observe its spectrum. The operation of concentrating polonium, as I shall point out later, is, moreover, a problem of great theoretical interest.

Recently, in collaboration with Debierne, I undertook to treat several tons of residues from uranium mineral with a view to preparing polonium. Initially conducted in the factory, then in the laboratory, this treatment finally yielded a few milligrams of substance about 50 times more active than an equal weight of pure radium. In the spectrum of the substance some new lines could be observed which appear attributable to polonium and of which the most important has the wavelength 4170.5 Å. According to the atomic hypothesis of radioactivity, the polonium spectrum should disappear at the same time as the activity and this fact can be confirmed experimentally,

I have so far considered radium and polonium only as chemical substances. I have shown how the fundamental hypothesis which states that radioactivity is an atomic property of the substance has led to the discovery of new chemical elements. I shall now describe how the scope of this hypothesis has been greatly enlarged by the considerations and experimental facts which resulted in establishing the theory of atomic radioactive transformations.

The starting-point of this theory must be sought in the considerations of the source of the energy involved in the phenomena of radioactivity. This energy becomes manifest as an emission of rays which produce thermal, electrical and light phenomena. As the emission occurs spontaneously without any known cause of excitation, various hypotheses have been advanced to account for the liberation of energy. One of the hypotheses put forward at the beginning of our research by Pierre Curie and myself consisted in assuming that the radiation is an emission of matter accompanied by a loss in weight of the active substances and that the energy is taken from the substance itself whose evolution is not yet completes and which undergoes an atomic transformation. This hypothesis, which at first could only be enunciated together with other equally valid theories, has attained dominant importance and finally asserted itself in our minds owing to a body of experimental evidence which substantiated it. This evidence is essentially the following: A series of radioactive phenomena exists in which radioactivity appears to be tied up to matter in an imponderable quantity, the radiation moreover not being permanent but disappearing more or less rapidly with time. Such are polonium, radioactive emanations and deposits of induced radioactivity.

It has been established moreover in certain cases that the radioactivity observed increases with time. This is what happens in the case of freshly prepared radium, of the emanation freshly introduced into the measuring apparatus, of thorium deprived of thorium X, etc.

A careful study of these phenomena has shown that a very satisfactory general explanation can be given by assuming that each time a decrease of radioactivity is observed there is a destruction of radioactive matter, and that each time an increase of activity is observed, there is a production of radioactive matter. The radiations which disappear and appear are, besides, of very varied nature and it is admitted that every kind of rays determined can serve to characterize a substance which is its source, and appears and disappears with it.

As radioactivity is in addition a property which is essentially atomic, the production or the destruction of a distinct type of radioactivity corresponds to a production or a destruction of atoms of a radioactive substance.

Finally, if it is supposed that radioactive energy is a phenomenon which is borrowed from atomic transformation, it can be deduced from this that every radioactive substance undergoes such a transformation, even though it appears to us to be invariable. Transformation in this case is only very slow and this is what takes place in the case of radium or uranium.

The theory I have just summarized is the work of Rutherford and Soddy, which they have called theory of atomic disintegration. By applying this theory it can be concluded that a primary radioactive substance such as radium undergoes a series of atomic transmutations by virtue of which the atom of radium gives birth to a train of atoms of smaller and smaller weights, since a stable state cannot be attained as long as the atom formed is radioactive. Stability can only be attained by inactive matter.

From this point of view one of the most brilliant triumphs of the theory is the prediction that the gas helium, always present in radioactive minerals, can represent one of the end-products of the evolution of radium, and that it is in the form of alpha rays that the helium atoms which are formed when radium atoms distintegrate are discharged. Now, the production of helium by radium has been proved by the experiments of Ramsay and Soddy, and it cannot now be contested that the perfectly defined chemical element, radium, gives rise to the formation of another equally defined element - helium. Moreover, the investigations done by Rutherford and his students have proved that the alpha particles emitted by radium with an electric charge are also to be found in the form of helium gas in the space where they have been recovered.

I must remark here that the bold interpretation of the relationship existing between radium and helium rests entirely upon the certitude that radium has the same claim to be a chemical element as have all the other known elements, and that there can be no question of regarding it to be a molecular combination of helium with another element. This shows how fundamental in these circumstances has been the work carried out to prove the chemical individuality of radium, and it can also be seen in what way the hypothesis of the atomic nature of radioactivity and the theory of radioactive transformations have led to the experimental discovery of a first clearly-established example of atomic transmutation. This is a fact the significance of which cannot escape anyone, and one which incontestably marks an epoch from the point of view of chemists.

Considerable work, guided by the theory of radioactive transformations, has led to approximately 30 new radioactive elements being envisaged, classified in 4 series according to the primary substance: these series are uranium, radium, thorium and actinium. The uranium and radium series can, in fact, be combined, for it seems to be proved that radium is a derivative of uranium. In the radium series the last known radioactive body is polonium, the production of which by radium is now a proven fact. It is likely that the actinium series is related to that of radium.

We have seen that helium gas is one of the products of radium distintegration. The helium atoms are detached from those of radium and its derivatives during the course of the transformation. It is supposed that after the departure of four atoms of helium, the radium atom yields one atom of polonium; the departure of a fifth helium atom determines the formation of an inactive body with an atomic weight believed to be equal to 206 (20 units below that of radium). According to Rutherford this final element is nothing more than lead, and this supposition is now being subjected to experimental verification in my laboratory. The production of helium from polonium has been directly proved by Debierne.

The relatively large amount of polonium prepared by Curie and Debierne has allowed an important study to be undertaken. This consists in counting a large number of alpha particles emitted by polonium and in collecting and measuring the corresponding volume of helium. Since each particle is a helium atom, the number of helium atoms is thus found which occupy a given volume and have a given weight. It can therefore allow us to deduce, in a general way, the number of molecules in a grammolecule. This number, known as Avogadro's constant, is of great importance. Experiments conducted on polonium have supplied a first value for this number, which is in good agreement with the values obtained by other methods. The enumeration of alpha particles is done by an electrometric method due to Rutherford; this method has been brought to perfection by means of a photographic recording apparatus.

Recent investigations have shown that potassium and rubidium emit a very feeble radiation, similar to the beta radiation of uranium and radium. We do not yet know whether we should regard these substances as true radioactive bodies, i.e. bodies in the process of transformation.

To conclude I should like to emphasize the nature of the new chemistry of radioactive bodies. Tons of material have to be treated in order to extract radium from the ore. The quantities of radium available in a laboratory are of the order of one milligram, or of a gram at the very most, this substance being worth 400,000 francs per gram. Very often material has been handled in which the presence of radium could not be detected by the balance, nor even by the spectroscope. And yet we have methods of measuring so perfect and so sensitive that we are able to know very exactly the small quantities of radium we are using. Radioactive analysis by electrometric methods allows us to calculate to within 1% a thousandth of a milligram of radium, and to detect the presence of 10⁻¹⁰ grams of radium diluted in a few grams of material. This method is the only one which could have led to the discovery of radium in view of the dilution of this substance in the ore. The sensitivity of the methods is still more striking in the case of radium emanation, which can be detected when the quantity present amounts, for example, to only 10⁻¹⁰ mm. As the specific activity of a substance is, in the case of analogous radiations, approximately in inverse proportion to the average life, the result is that if the average life is very brief, the radioactive reaction can attain an unprecedented sensitivity. We are also accustomed to deal currently in the laboratory with substances the presence of which is only shown to us by their radioactive properties but which nevertheless we can determine, dissolve, reprecipitate from their solutions and deposit electrolytically. This means that we have here an entirely separate kind of chemistry for which the current tool we use is the electrometer, not the balance, and which we might well call the chemistry of the imponderable.

1. H. Becquerel, Compt. Rend., (1896).

2. P. Curie and M. Curie, Compt. Rend., (1898); (1899).

3. M. Curie, Rev. Gen. Sci., (1899); Rev. Sci., (1900).

From Nobel Lectures, Chemistry 1901-1921, Elsevier Publishing Company, Amsterdam, 1966

To cite this page MLA style: "Marie Curie - Nobel Lecture: Radium and the New Concepts in Chemistry".
Nobelprize.org. Nobel Media AB 2014. Web. 8 Jun 2018. <http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1911/marie-curie-lecture.html>

Recommended:

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Nobel Lecture, December 11, 1911 Some 15 years ago the radiation of uranium was discovered by Henri Becquerel, and two years later the study of this phenomenon was extended to other substances, first by me, and then by Pierre Curie and myself.

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Marie Curie and The Science of Radioactivity

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The life of Marie Curie, from the AIP Center for History of Physics. Text by Naomi Pasachoff and many illustrations describe Curie's contributions to the science of radioactivity and discovery of radium, and her life as a woman scientist and creator of the Radium Institute

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The Manhattan Project: Making the Atomic Bomb. Manhattan Project Chronology.

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Manhattan Project Signature Facilities | History of the Atomic Age | atomicarchive.com

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This collection is a list of the Department of Energy's Manhattan Project Signature Facilities approved by the Departmental Corporate Board on Historic Preservation in December 1999. Taken together, the eight Signature Facilities provide the core for DOE's ability to successfully interpret, whether in situ or through museum or other interpretive setting, the Manhattan Project mission of developing atomic bombs during World War II.

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Designs of Two Bombs

The Manhattan Project produced two different types of atomic bombs, code-named Fat Man and Little Boy. Fat Man, which was dropped on Nagasaki, was the more complex of the two. A bulbous, 10-ft. bomb containing a sphere of the metal plutonium 239, it was surrounded by blocks of high explosives that were designed to produce a highly accurate and symmetrical implosion. This would compress the plutonium sphere to a critical density and set off a nuclear chain-reaction. Scientists at Los Alamos were not entirely confident in the in the plutonium bomb design, so they scheduled the Trinity test.

The Little Boy type of bomb, which was dropped on Hiroshima, had a much simpler design than the Fat Man model that had been tested at Trinity. Little Boy triggered a nuclear explosion, rather than implosion, by firing one piece of uranium 235 into another. When enough U235 is brought together, the resulting fission chain reaction can produce a nuclear explosion. But the critical mass must be assembled very rapidly; otherwise, the heat released at the start of the reaction will blow the fuel apart before most of it is consumed. To prevent this inefficient pre-detonation, the uranium bomb uses a gun to fire one piece of U235 down the barrel into another. The bomb's gun-barrel shape was believed to be unquestionably reliable and had never been tested. In fact, testing was out of the question since producing Little Boy had used all of the purified U235 produced to date; therefore, no other bomb like it has ever been built.

Detonated by a mechanism that resembled a cannon, Little Boy had a muzzle or target that was a hollowed-out subcritical mass of uranium. The cannon ball was another subcritical mass of uranium, which fit perfectly into the hollow of the target as a plug. The plug was propelled down the cannon barrel by several thousand pounds of high explosive. When it hit, the combination of compression and increased mass pushed the uranium to the supercritical level and the bomb went off.

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From FDR to Oppenheimer

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On this day in 1943, President Franklin D. Roosevelt writes a letter marked "secret" to leading Manhattan Project physicist J. Robert Oppenheimer. In the letter, Roosevelt sought to smooth over the growing antagonism between Oppenheimer and General Leslie Groves, the military leader in charge of the project.

Roosevelt began by congratulating Oppenheimer (or "Oppie" as he was known to colleagues and friends) on the progress of a "highly important and secret program of research, development and manufacture with which you are familiar." No mention was made, of course, of the phrase "Manhattan Project" or "atomic bomb." Roosevelt conveyed a sense of urgency in solving "the problem" and bringing the project to fruition. He stressed the project's bearing on national security.

Roosevelt's letter acknowledged Oppenheimer as the leader of an elite group of scientists operating under strict security and under "very special conditions." He had received reports that the brain trust of scientists tapped to deliver an atomic weapon were starting to snap under the pressure of trying to meet what they saw as an impossible deadline. Oppenheimer and Groves frequently clashed over the scientists living and working conditions. The small isolated community resented living under heavy guard in the desert of New Mexico. Many of the experts had doubts the bomb could even be built at all and questioned the wisdom of working with such dangerous material.

Roosevelt appealed to Oppenheimer to convince the group of the necessity of the restrictions and asked him to convey his appreciation for their hard work and personal sacrifice. Roosevelt expressed his faith that "whatever the enemy may be planning, American science will be equal to the challenge." The letter reflected Roosevelt's natural ability to rally morale-whether it was subduing revolt among physicists working on a crucial new weapon or reassuring American mothers of the need for food rationing in a time of war.

Two years later, at a test site near Alamogordo, New Mexico, the first atomic bomb was successfully detonated. Roosevelt would not live to decide whether or not to use the new and powerful weapon in World War II. He died on April 12, 1945, leaving the decision to his successor, Harry S. Truman. Truman authorized the use of the world's first atomic weapons against Japan on August 6 and 9, 1945.

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Race for the Superbomb | Article

Hans A. Bethe

Hans A. Bethe, (1906 - 2005)

When physicist Hans Bethe first heard of the atomic bomb project he thought it an impractical idea and he didn't want to get involved with it. He told a biographer after the war that, "I considered... an atomic bomb so remote that I completely refused to have anything to do with it." But he was also desperate to make some contribution to the war effort against the Nazis, especially after the fall of France. So in the summer of 1942, when Robert Oppenheimer pulled together a group of distinguished physicists to work at Berkeley on a design for the bomb, Bethe accepted the invitation. He and his young wife Rose drove across the country from Cornell University, where he was teaching, to California, stopping on the way to pick up their best friends Edward Teller and his wife Mici at the University of Chicago. When Bethe saw the atomic pile that physicist Enrico Fermi had built at the University he became convinced that the atomic bomb would probably work.

Hans Bethe was born in Strasbourg, Germany, in 1906, the son of a university psychologist. He started his university studies in Frankfurt in 1924 and in 1932 joined the faculty at Tübingen University. Almost as soon as Adolf Hitler became Chancellor of Germany in January 1933, hundreds of Jewish academics were fired from their jobs. Although Bethe didn't consider himself a Jew--his mother was Jewish his father wasn't--the Third Reich did. He learned of his dismissal from one of his students who read about it in the paper. Bethe was able to find another position in Munich with his mentor, Arnold Sommerfeld, but when Cornell University offered him an assistant professorship in the summer of 1934, he accepted and emigrated to America.

It was in the 1930s that Bethe achieved his greatest accomplishment by developing a theory for the production of energy in stars. It was work for which he would receive a Nobel Prize in 1967. Following the summer at Berkeley spent on the atomic bomb design, Bethe was recruited by Oppenheimer to head the theoretical division at the new weapons laboratory that was being set up in Los Alamos, New Mexico. Teller was disappointed not to have been picked for the post himself. Bethe remembers that it, "was a severe blow to Teller, who... considered himself, quite rightly as having seniority over everyone then at Los Alamos." Tensions increased between the old friends, when Teller, who was supposed to be heading a group working on implosion calculations, began to concentrate instead on the feasibility of a hydrogen bomb.

Following the success of the Manhattan Project and the end of the war, Bethe returned to Cornell to resume teaching and his academic research. When the Soviet Union conducted its first atomic test in August 1949, Teller went to visit Bethe in the hopes of persuading him to return to Los Alamos to work on the superbomb. Bethe agonized over the decision. But ultimately he concluded that in a war fought with hydrogen bombs, "even if we were to win it, the world would not be... like the world we want to preserve. We would lose the things we were fighting for." Bethe called Teller and told him he had decided against working on the project.

Bethe remained vigorously opposed to the H-bomb throughout his life although, he continued to return to Los Alamos as a consultant. He became a member of the President's Science Advisory Committee in 1956, a position he held until 1959. It was in this capacity that he was involved in the failed negotiations with the Soviet Union for a ban on nuclear testing. Nevertheless, he has continued to argue for slowing down the arms race and for nuclear disarmament. In February 1997, as the Senate was preparing for a debate on the ratification of the Comprehensive Test Ban Treaty, the 90-year-old physicist wrote a letter to President Clinton, urging him to stop not only all tests of nuclear weapons but also the sponsorship of "computational experiments, or even creative thought designed to produce new categories of nuclear weapons."

Edward Teller, (1908 - 2003)

Of all the scientists who worked on the U.S. nuclear weapons program none have led more controversial a career than Edward Teller. Described by one Nobel Prize winner in physics as "one of the most thoughtful statesmen of science," and by another as "a danger to all that's important," Teller was recognized by most of his colleagues as being one of the most imaginative and creative physicists alive. But at the same time, his single-minded pursuit of the hydrogen bomb, and his autocratic style alienated many of the scientists he worked with.

The man who would one day be known as the father of the hydrogen bomb in the U.S. was born into a Jewish family on January 15, 1908 in Budapest, Hungary. He grew up during a particularly turbulent time in Hungarian history. Following a briefly successful communist regime in 1919, the country was ruled by a virulently anti-semitic fascist dictator, Nicholas Horthy.

The political upheavals meant the young Teller was only too happy to leave his homeland in 1926 to study in Germany. In 1930 he got his PhD in theoretical physics from the University of Leipzig. Although he accepted a research post in 1931 following his graduation, Teller realized that Hitler's rise to power meant that he should leave Germany as soon as he could. Many years later he told his biographer that "the hope of making an academic career in Germany for a Jew existed before Hitler came and vanished the day he arrived."

In 1935 Teller emigrated to the United States to take up a teaching position at George Washington University. His first years in the U.S. marked a new phase of his career: His postdoctoral research had been in quantum mechanics; at George Washington University, he would begin a very productive collaboration with Russian emigré George Gamow in nuclear physics. At the outbreak of the Second World War, scientists became aware that the nucleus of a uranium atom could be split releasing enormous amounts of energy. It began to seem feasible that this energy could be used to create a weapon of unprecedented power. Teller was among the first scientists recruited to work on the Manhattan Project that was working to develop such a bomb.

It was Italian-born physicist Enrico Fermi who first got Teller thinking about an H-bomb. In September 1941, before the United States had even built an A-bomb, he suggested to Teller that an atomic bomb might heat a mass of deuterium (an isotope of hydrogen) sufficiently to ignite a thermonuclear reaction. In the summer of 1942, when Teller joined a group of distinguished physicists who were brainstorming about a design for the atomic bomb, he diverted much of the discussion to the feasibility of a superbomb. Teller travelled to California with his old friend Hans Bethe who remembers that even on the way out to Berkeley Teller was already thinking about the super: "Teller told me that the fission bomb [atomic bomb] was all well and good and, essentially, was now a sure thing.. He said that what we really should think about was the possibility of...the hydrogen bomb."

Shortly after Teller arrived at the newly established weapons laboratory in Los Alamos, his obsession with the H-bomb caused tensions with other scientists, particularly Bethe. Bethe remembers that "he declined to take charge of the group which would perform the detailed calculation on the implosion and since the theoretical division was very shorthanded it was necessary to bring in new scientists to do the work that Teller declined to do."

Teller left Los Alamos at the end of the war, returning to the University of Chicago. But when the Soviet Union conducted its first test of an atomic device in August 1949, he did his best to drum up support for a crash program to build a hydrogen bomb. Teller argued that a superbomb was essential to the very survival of the U.S., "If the Russians demonstrate a super before we possess one, our situation will be hopeless." Truman eventually agreed, calling for a hydrogen bomb program at the end of January 1950.

During the course of 1950, Teller was frustrated with the progress of the program. When his initial concept for the bomb didn't appear to work, he insisted that the problem was caused by a shortage of theoreticians at Los Alamos and a lack of imagination. These accusations served to further distance him from the other scientists. When he and mathematician Stanislaw Ulam finally came up with an H-bomb design that would work, Teller was not chosen to head the project. He left Los Alamos and soon joined the newly established Lawrence Livermore laboratory, a rival weapons lab in California.

It was Robert Oppenheimer's security clearance hearings in 1954 that was the occasion for the final rift between Teller and many of his scientific colleagues. Oppenheimer, the scientific director of the Manhattan Project, had come under scrutiny because of his affiliation with left-leaning political organizations in the 1930s and also because of his consistent opposition to the hydrogen bomb. At Oppenheimer's hearings, Teller testified that "I feel I would prefer to see the vital interests of this country in hands that I understand better and therefore trust more." The testimony enraged many in the scientific community, who felt it was a terrible betrayal of the hardworking and loyal Oppenheimer.

Teller has continued to be a tireless advocate of a strong defense policy, calling for the development of advanced thermonuclear weapons and continued nuclear testing. During the Vietnam War his proposals so incensed radical protestors that some of them actually labeled him a "war criminal." In the 1980s, he was a vigorous proponent of a proposed new defense system that came to be known as the Strategic Defense Initiative or more popularly as Star Wars.

Enrico Fermi, (1901 - 1954)

The story that his wife Laura tells, is that Enrico Fermi's interest in physics can be traced back to the death of his older brother Giulio when Fermi was just 14. The two boys, just a year apart in age, had been incredibly close. And Giulio's death left Enrico inconsolable. Shortly afterwards he found two old physics textbooks at market that were written by a Jesuit physicist in 1840. Fermi was so intrigued by them, he read them straight through, apparently, not even noticing that they were in Latin. From that point on, physics consumed him.

When Fermi was 17 he applied to the University of Pisa. His entry essay was so advanced that it amazed the examiner who thought it suitable for a graduating doctoral student. In 1926 he became a professor of theoretical physics at the University of Rome. And in the 1930s, he began a series of experiments in which he bombarded a variety of different elements with neutrons. Fermi did not realize until later that he had, in fact, succeeded in splitting the uranium atom. It was for this work that the Nobel Committee awarded him the 1938 prize for physics.

The call from Stockholm was a life-saver for the Fermi family. The night before, a bloody pogrom had taken place in Germany that became known as Kristallnacht. And just a few months earlier, the Italian Fascists had implemented a new anti-Semitic law that claimed: "Jews do not belong to the Italian race." Although Fermi wasn't Jewish, his wife Laura was. The award ceremony gave the family an opportunity to escape Italy and emigrate to America.

At Columbia University in New York, Fermi realized that if neutrons are emitted in the fissioning of uranium then the emitted neutrons might proceed to split other uranium atoms, setting in motion a chain reaction that would release enormous amounts of energy. Together with Hungarian physicist Leo Szilard, Fermi ultimately succeeded in constructing the world's first atomic pile in a squash court under the stands of Stagg Field at the University of Chicago. And on December 2, 1942, it produced the first controlled, self-sustaining nuclear chain reaction. Fermi had succeeded in taking one of the first steps to making an atomic bomb.

One of the participants at that momentous occasion wrote: "Even though we had anticipated the success of the experiment, its accomplishment had a deep impact on us. For some time we had known that we were about to unlock a giant; still we could not escape an eerie feeling when we knew we had actually done it."

After working on the Manhattan Project during the war, Fermi was appointed to the General Advisory Committee, the panel of scientists that advised the Atomic Energy Commission. In October 1949, the GAC met to discuss whether the U.S. should initiate a crash program to build the superbomb. After the meeting, Fermi and Isidor Rabi co-authored a minority addendum to the committee's report. It described the H-bomb in the harshest possible language: "It is clear that such a weapon cannot be justified on any ethical ground... The fact that no limits exist to the destructiveness of this weapon makes its very existence and the knowledge of its construction a danger to humanity as a whole. It is necessarily an evil thing considered in any light."

However, when President Truman ordered a crash program to build the superbomb a couple of months later, Fermi returned temporarily to Los Alamos to help with the calculations. He joined the effort hoping to prove that making a superbomb just wasn't possible.

J. Robert Oppenheimer

J. Robert Oppenheimer, (1904 - 1967)

Robert Oppenheimer was born on April 22, 1904, into a wealthy, New York, Jewish family. They lived in an apartment overlooking the Hudson River and vacationed in a summer home on Long Island. As a 17-year-old, Oppenheimer went to Harvard where a classmate says he "intellectually looted the place." But it was after Harvard that Oppenheimer found his intellectual passion. First at Cambridge University in England and then at Göttigen University in Germany, the young American scholar began making his mark in quantum theory. By the time he returned to America, he'd published more than a dozen articles and established a reputation as a theoretical physicist.

In the 1930s, Oppenheimer became drawn into left-wing politics. In part, this may have been a reaction to the rise of Nazism in Germany where his relatives were suffering under increasingly severe anti-semitic laws, but it may also have been a reaction to the Great Depression. Many of his students were unable to get jobs and Oppenheimer would say, "I began to understand how deeply political and economic events could affect men's lives." He got involved with a number of left-leaning organizations and began making an annual donation of about $1,000 to various funds associated with the Communist Party. When he joined the atomic bomb project he admitted in his security questionnaire that he had been "a member of just about every Communist Front organization on the West Coast." It was an admission that cast suspicion on him and eventually played a large role in the loss of his security clearance.

In 1941 Oppenheimer was brought into the atomic bomb project. His first task was to calculate the critical mass of uranium-235, i.e. the amount of uranium needed to sustain a chain reaction. The following summer he gathered together at Berkeley a small group of some of the best theoretical physicists in the country to talk about the actual bomb design. The group, which he dubbed the "luminaries," included Hans Bethe and Edward Teller. By the end of the summer they concluded that the bomb project would require a major scientific effort.

General Leslie Groves, the army officer in charge of the bomb project wanted Oppenheimer to be the scientific director of the program, despite what he would call the "snag" of Oppenheimer's political past. After the war, he explained why: "He's a genius. A real genius... Why, Oppenheimer knows about everything. He can talk to you about anything you bring up. Well, not exactly. I guess there are a few things he doesn't know about. He doesn't know anything about sports."

Together the two men picked out a site for a new laboratory for the project. It had to be isolated, but it needed to be easily accessible, it needed an adequate supply of water, and a moderate climate for year-round construction. Oppenheimer took Groves to a boys' school on a mesa in the New Mexico desert, which he had visited as a young man. The site became the location for the top secret Los Alamos weapons laboratory.

By July 1945, Los Alamos was ready to test its bomb. Oppenheimer sent a cryptic telegram to scientists back at Berkeley: "Any time after the 15th would be a good time for our fishing trip...As we do not have enough sleeping bags to go around, we ask you please do not bring anyone with you." The test, code-named "Trinity," took place on July 16. It exploded with a force equivalent of 18,000 tons of TNT. Recalling the scene, Oppenheimer said: "A few people laughed, a few people cried, most people were silent. There floated through my mind a line from the "Bhagavad-Gita" in which Krishna is trying to persuade the Prince that he should do his duty: "I am become death: the destroyer of worlds."

After the war Oppenheimer achieved nation-wide recognition as the "father of the A-bomb," and he was widely quoted as the moral conscience of those who had worked on the project. "In some sort of crude sense, which no vulgarity, no humor, no overstatement can quite extinguish," he would say, "the physicists have known sin, and this is a knowledge which they cannot lose." He also rose to prominence as a scientific advisor to the Federal Government. He pushed hard for international control of atomic energy, and was appointed Chairman of the General Advisory Committee to the Atomic Energy Commission. It was in this role that he voiced strong opposition to the development of the H-bomb.

His political past and his resistance to the hydrogen bomb ultimately had devastating consequences for his career. In 1953, the Atomic Energy Commission suspended his security clearance. Despite testimonials from scores of witnesses during the hearings, his clearance was not reinstated. Oppenheimer returned to academic life, but as one colleague would say, the public ordeal had broken his spirit.

Stanislaw M. Ulam (1909 - 1984)

One night in 1946, Stanislaw Ulam, a young mathematics professor was overwhelmed by a violent headache. When he tried to talk he found he could produce nothing but a meaningless mumble. He was rushed to a hospital where the surgeon drilled a hole in his skull and found his brain in an acute state of inflammation. The doctors applied penicillin liberally and Ulam lapsed into a coma.

The diagnosis was encephalitis. And Ulam's wife and friends worried that he would suffer permanent brain damage. But that was far from the case. The mathematician went on to produce some of his best work after his recovery. And, in fact, it was playing solitaire while convalescing, that Ulam first thought up the "Monte Carlo" method. Together with an old friend, mathematician John von Neumann, Ulam developed the procedure into an extremely useful calculating tool that enabled mathematicians to solve complicated problems by making approximations. It was put to almost immediate use by scientists working on nuclear weapons.

Ulam had first come to the United States from Poland for a few months in 1935 at von Neumann's invitation to work at the Institute of Advanced Studies in Princeton. He left his homeland for good in 1939 with his 16-year-old brother Adam. His father and uncle saw them off. It was the last time the brothers ever saw either men. Along with the rest of the Ulam family, they became victims of Hitler's holocaust.

In 1943 Ulam received a letter from physicist Hans Bethe offering him a job doing some war work. He remembers the letter was cryptic, "I received an official invitation to join an unidentified project that was doing important work, the physics having something to do with the interior of stars." The location was Los Alamos, New Mexico, the assignment: making an atomic bomb.

After a brief stint teaching at the University of Southern California, Ulam returned to the weapons laboratory at Los Alamos in 1946. And when President Truman announced in January 1950 that the United States was about to embark on an all-out effort to develop a hydrogen bomb, Ulam began calculating whether physicist Edward Teller's design for the superbomb would work. He comments: "We filled page upon page with calculations... I do not know how many man hours were spent on this problem."

Ultimately, Ulam and a fellow mathematician Cornelius Everett concluded that Teller's model was a "fizzle" and that it would never work. The results caused tensions between Ulam and Teller. But a year later Ulam accidentally came up with a new scheme that would prove to be a breakthrough, and he reluctantly took it to Teller. Teller recognized that, though there were problems with the idea, Ulam had hit on the solution. Together the two men converted it into a design for the superbomb that everyone at Los Alamos immediately recognized would work.

Their plan was to place an atom bomb inside a heavy shell that would also contain a capsule of hydrogen fuel. When the atom bomb exploded, in the fraction of a second before the whole assembly blew itself apart, the shell would confine the radiation from the atomic blast long enough to heat and compress the hydrogen fuel, setting off a fusion reaction. Central to Ulam's idea was the use of material surrounding the fuel capsule that would magnify the energy of the radiation.

Decades later physicist Hans Bethe wrote: "The new concept was to me, who had been rather closely associated with the program, about as surprising as the discovery of fission had been to physicists in 1939... Such miracles incidentally do happen occasionally in scientific history but it would be folly to count on their occurrence."

Klaus Fuchs

Klaus Fuchs, (1911 - 1988)

His colleagues at the atomic weapons laboratory in Los Alamos, New Mexico, remembered Klaus Fuchs as a shy, reclusive man, and an exceptionally talented scientist who worked extremely hard. And so most of them were stunned and horrified when, in February 1950, he was charged with having given atom bomb secrets to the Soviets.

In his confession, attempting to explain the terrible betrayal of his friends, colleagues and adoptive country, Fuchs said that his father had taught him to stand up for what he believed, even if his beliefs were at odds with accepted convention. And that, Fuchs explained, was why as a student in Germany, he'd joined the Communist Party. He was convinced the Communists were the only political organization able to fight the increasing influence of the Nazis.

Klaus Fuchs was born on December 29, 1911 in Rüsselsheim, Germany. His father was a Lutheran minister who was deeply committed to socialist ideology. The younger Fuchs became interested in politics as a student. Once Adolf Hitler became Chancellor of Germany in 1933, Fuchs' political affiliations made him a target for the Nazis. He went into hiding for several months before escaping to Britain via France. Years later he explained that the Communist Party sent him out of Germany. "They said I must finish my studies because after the revolution in Germany people would be required with technical knowledge to take part in the building up of the Communist Germany."

Fuchs quickly proved himself to be a brilliant young scientist. After receiving a PhD in physics from the University of Bristol, he was recruited to work in Edinburgh with one of the pioneers of quantum mechanics. After the war broke out, even though his communist past was known, the British granted him security clearance and he was recruited to work on the atom bomb. In his confession, Fuchs remembers being asked to help, "on some war work. I accepted it and started work without knowing at first what the work was... When I learned the purpose of the work I decided to inform Russia and I established contact through another member of the Communist Party."

In 1943 Fuchs was among the British scientists sent to the U.S. to collaborate with Americans working on the atom bomb. At first he was assigned to a team at Columbia University in New York. Later he was transferred to the weapons laboratory in Los Alamos, New Mexico, where he worked in the theoretical division under Hans Bethe. He couldn't have been better placed to provide the Soviets information about the U.S. atomic bomb program.

Fuchs made contact with a Soviet courier almost as soon as he'd arrived in the U.S, a man he knew only as Raymond, but who was in fact Harry Gold. Fuchs and Gold met several times. At one meeting in Santa Fe, Fuchs gave Gold a precise drawing with measurements of the "Fat Man" bomb, the bomb the United States dropped on Nagasaki at the end of World War II.

After the war ended, Fuchs made sure he understood everything U.S. scientists knew about making hydrogen bombs. In April 1946, he attended a top-secret, three-day conference at Los Alamos that reviewed the wartime work on the superbomb. Shortly afterwards he filed a patent with mathematician John von Neumann for an initiator for the hydrogen bomb. And then just before returning to Britain he reviewed every document in the Los Alamos archives on thermonuclear weapons design.

In Britain, Fuchs began working at the Harwell Atomic Research facility. But it didn't take him long to reestablish his Soviet contacts. In September 1947, he met with his new intelligence agent, Alexander Feklisov, in a north London pub. Asked ten questions about the superbomb, Fuchs described to Feklisov certain structural characteristics of the weapon. In March of 1948, he met Feklisov again. This time he handed over material that some Russian physicists now say proved to be of great importance to the Soviet hydrogen bomb. It contained a detailed description of the classical Super, as the first design for the hydrogen bomb was known, as well as Fuchs' own concept for an initiator.

Fuchs' world finally began falling apart at the end of 1949. On December 21, a British intelligence officer informed the physicist that he was suspected of having given classified nuclear weapons information to the Soviet Union. Fuchs repeatedly denied the accusations, but he ultimately broke down and agreed to make a statement. He was brought to trial at the Old Bailey in London, where the audience included some 80 newspaper reporters, two U.S. Embassy representatives, the mayor of London and the Duchess of Kent. The chief prosecutor was Attorney General Hartley Shawcross who was widely known for his role at the Nuremberg Trials.

The trial lasted less than two hours. Fuchs pleaded guilty. He said that he had not wanted to hurt his friends at Harwell, and that he hoped his confession would help atone for his wrongdoing. Until shortly before his trial began, Fuchs assumed the maximum penalty for his crimes was death. In fact, since the USSR had not been an enemy at the time of the crimes for which Fuchs was charged, under British law he could only be sentenced to 14 years. He was released from prison after nine and immediately left Britain for East Germany where he resumed his scientific career.

Isidor Rabi (1898-1988)

Isidor Rabi was awarded the Nobel Prize for physics in 1944 for developing a method of measuring the magnetic properties of atoms, molecules and atomic nuclei. This research made possible the subsequent development of the laser and the atomic clock. During the war Rabi worked at the Radiation Laboratory of the Massachusetts Institute of Technology developing radar. He turned down an invitation to become the deputy director of the Manhattan Project, although, he did visit the weapons laboratory at Los Alamos to consult with the scientists working on the atomic bomb program. After the war, he pushed hard for the international control of atomic energy and he vigorously opposed the development of the hydrogen bomb.

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Scientists and Mathematicians in America | American Experience | PBS

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Race for the Superbomb | Article When physicist Hans Bethe first heard of the atomic bomb project he thought it an impractical idea and he didn't want to get involved with it. He told a biographer after the war that, "I considered... an atomic bomb so remote that I completely refused to have anything to do with it."

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The Development and Proliferation of Nuclear weapons

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The Development and Proliferation of Nuclear weapons

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The Nobel Prize Perspective

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ECG, Willem Einthoven, Einthoven, Electrocardiogram, cardiogram, heart condition, ECG curves, game, read more

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Growing up in Oak Ridge, TN

One man's story

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Some profiles include a detailed description of the person's life and work, while for others all the information we know is their name and Manhattan Project location. We have also included profiles of early nuclear pioneers, Manhattan Project experts, and German scientists who worked on Nazi Germany's efforts to develop the bomb.

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Nobel Prize in Physics

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Nobelprize.org, The Official Web Site of the Nobel Prize

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Photographs and accounts of the chemists

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These ideas of Einstein were pure theory at the time. He had no experimental data to confirm the truth of his equation, but suggested that research in radioactivity and atom-bombardment might furnish the proof.

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A historical perspective

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The Manhattan Project: Making the Atomic Bomb | History of the Atomic Age | atomicarchive.com

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The Manhattan Project: Making the Atomic Bomb is a short history of the origins and development of the American atomic bomb program during World War II.