Harnessing of Nuclear Fission

The Story Of The Atomic Bomb


James Richard Fromm

Late in 1938, in Berlin-Dahlem, an experiment in nuclear chemistry touched off a wave of excitement throughout the world which even reached the front pages of the most conservative newspapers.  At the Kaiser Wilhelm Institute for Chemistry, only a few miles from Hitler's Chancellery, three researchers had proceeded to repeat some experiments first performed by Enrico Fermi (1901-1954) in Rome in 1934.

fermi.jpg (45058 bytes)

Enrico Fermi

The Italian scientist, in an attempt to produce the Curies' artificial radioactivity in the very heavy elements by bombarding them with neutrons, believed he had created an element (No. 93) even heavier than uranium.

Two of these scientists in Berlin-Dahlem, Otto Hahn (1879-1968) and Lise Meitner (1878-1968), had already confirmed Fermi's results, and by 1936 it was proposed to name this new element Ansonio after an ancient name of Italy.

hahn.gif (75914 bytes)

Otto Hahn

meitner.gif (35721 bytes)

Lise Meitner

strassmann.jpg (79195 bytes)

Fritz Strassmann

Later, Fritz Strassmann (1902-1980) joined the team and together they continued with these experiments. On January 6, 1939, they observed a strange result which they published two months later in Die Naturwissenschaften. According to Hahn and Strassmann, the bombardment of uranium with neutrons had split the uranium atom almost in half! The smash-up had produced what they had reason to believe were two different and lighter elements, isotopes of barium and krypton (U92 Ba56 + Kr36). Previously only bits of the heavier atoms had been chipped away. No new theory or explanation was offered for this unexpected effect.

What was even more startling than this transmutation was the announcement of the three scientists that during this spectacular change their oscilloscope recorded a release of energy equivalent to 200,000,000 electron volts. The Germans were completely at a loss for a logical explanation of this phenomenon which they had witnessed. Hahn was overcome by his interest in the chemical change, and the problem of the energy change escaped him. Dr. Lise Meitner, a mathematical physicist, knew, however, that something new and tremendously important had happened in the subatomic world of the nucleus of uranium. She pondered deeply over the probable mechanism of this change. In the meantime, however, the purge of non-Aryans and other intellectuals from German universities under Hitler caught up with the sixty-year-old woman scientist.

Born in Vienna, the daughter of a lawyer, Lise chose scientific research as a career and went to Berlin before World War I to assist both Max Planck (1858-1947) and Fritz Haber (1868-1934).

planck.jpg (14540 bytes)

Max Planck

haber.gif (10828 bytes)

Fritz Haber

By 1917 she was made head of the physics department of the Kaiser Wilhelm Institute at the time that Otto Hahn was head of its chemistry department. Working with him in that year she had discovered and isolated a new element No. 91--protoactinium (protactinium).

In spite of a lifetime of distinguished scientific work in Europe, during an intensified period of purges and atrocities Lise Meitner was finally marked by the Nazis as a Jew for arrest and a concentration camp. Early in 1939, therefore, she "decided that it was high time to get out with my secrets. I took a train for Holland on the pretext that I wanted to spend a week's vacation. At the Dutch border I got by with my Austrian passport, and in Holland I obtained my Swedish visa." Meitner, of course, wanted to escape the concentration camp but, even more important, she desperately needed to get out of Germany because she felt that she had an interpretation of the Hahn-Strassmann experiment--an explanation whose implications might change the course of history. On the basis of mathematical analysis Meitner saw in the Berlin experiment a splitting or fission of the nucleus of uranium into two almost equal parts. This atomic fission was accompanied by the release of stupendous nuclear energy resulting from the actual conversion of some of the mass of the uranium atom into energy in accordance with Einstein's Mass-energy law. This was her greatest contribution.

Albert Einstein

Back in 1905, Albert Einstein (1879-1955), in developing his theory of relativity, announced that there was no essential difference between mass and energy. According to his revolutionary thinking, energy actually possessed mass and mass really represented energy, since a body in motion actually possessed more mass than the same body at rest. Instead of two laws--the law of the conservation of mass, and the law of conservation of energy--there was only one law, the law of the equivalence and conservation of mass-energy. Einstein advanced the idea that ordinary energy had been regarded as weightless through the centuries because the mass it represented was so infinitesimally small as to have been missed and ignored. For example, the amount of heat energy required to change 300,000 tons of water into steam is equivalent to less than 1/30 once of matter.

Einstein published a mathematical equation to express the eqivalency of mass and energy. The equation is


where E represents energy in ergs, M is mass in grams, and C is the velocity of light in cm/sec. This last unit is equal to 186,000 miles per second. When this number is multiplied by itself as indicated in the formula, we get a tremendously large number; hence, E becomes an astronomically huge equivalent. For example, one pound of matter (one pound of coal or uranium) is equivalent to about 11 billion kilowatt hours, if completely changed into energy. Compare this figure with the burning (chemical change rather than nuclear change) of the same pound of coal, which produces only about 8 kilowatt hours of energy. In terms of energy produced, therefore, a chemical change such as burning is an extremely inefficient energy-producing process in comparison to the release of energy locked up in the nucleus of an atom (nuclear reaction). In other words, the available nuclear energy of coal is about 2 billion times greater than the available chemical energy of an equal mass of coal.

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. If the tremendously great electrical forces, the binding energy, that held the different particles inside the nucleus of the atom of radium or other elements could be suddenly released, Einstein's ideas might be shown to be true. The first bit of confirmation came in 1932. That was the year in which the neutron was discovered. But the neutron was not the bullet used in the bombardment experiments. High-speed hydrogen ions or protons were the battering rams employed. John Douglas Cockcroft (1897-1967) and E.T.S.Walton (1903-1995), working in Rutherford's laboratory, ionized hydrogen gas by removing their electrons and then accelerating the resulting protons in a transformer-rectifier high-voltage apparatus to an energy of 700,000 volts.

cockcroft.gif (10953 bytes)

John Douglas Cockcroft

walton.gif (11412 bytes)

E.T.S. Walton

The very swift protons then were made to strike a target of lithium metal. The lithium atom was changed into helium ions with energies many times greater than those of the proton bullets employed. This additional energy apparently came as a result of the partial conversion of some of the mass of lithium into helium in accordance with the following nuclear reaction:

Lithium + Hydrogen Helium + Energy

3Li7 + 1H1 22He4 + 17 M.E.V.

Mass 7.0180 + Mass 1.0076 2(Mass 4.0029)

Mass 8.0256 Mass 8.0058

This equation (8.0256 8.0058) seems to show a condition of imbalance, for the whole is less than the sum of its parts. There is an approximate loss of Mass 0.02--a fatal decimal that was to shake the world.  This loss of mass is accounted for by its conversion into the extra energy of the swiftly moving helium nuclei produced.  This energy turns out to be the exact mass equivalent as determined by Einstein's energy-mass equation, E=MC2.  However, the method used by these experimenters was extremely inefficient; only one out of several billion atoms actually underwent the change.  There was, therefore, no great excitement over this bit of scientific news.

irene-fred.jpg (64658 bytes)

Irene & Frederic Joliot-Curie
1897-1956 & 1900-1958

But publication of the energy release in the Hahn-Strassmann experiment not only revived the old interest, but raised it to a fever heat.  Before Meitner had reached Stockholm in her flight from the Nazis Irene Joliot-Curie (1897-1956) and Frederic Joliot-Curie (1900-1958) had obtained the same effect independently of the German investigators. In Stockholm, Lise Meitner communicated her thoughts regarding uranium fission to her nephew Dr. Robert O. Frisch (1904-1979), another German refugee who was then working in the laboratory of the world-famous atom-scientist, Niels Bohr (1885-1962), in Copenhagen. On January 15, 1939, Bohr's laboratory confirmed the Hahn experiment. Frisch was terribly excited.  He sent the news immediately to Bohr, who had just reached the United States for a stay of several months to discuss various scientific matters with Einstein at the Institute for Advanced Study at Princeton, New Jersey.

frisch2.jpg (28933 bytes)

Robert Otto Frisch

Bohr.jpg (17981 bytes)

Niels Bohr

Bohr, too, became excited at the news and communicated it to other scientists. Within a few days three American research groups confirmed the experiment.

dunning.jpg (3647 bytes)

John R. Dunning

On January 25, 1939, Fermi, John R. Dunning (1907-1975), and associates repeated the Hahn experiment with the help of the Columbia University 75-ton cyclotron located in the rock-hewn vault underneath the Physics building. They obtained the violent splitting of uranium, and their photographs showed high peaks of discharge of 200,000,000 electron volts. Merle Antony Tuve (1901-1982), Lawrence Randolph Hafstad (1904-1993), and Richard Brooke Roberts (1910-1980), working in the Department of Terrestrial Magnetism of the Carnegie Institute of Washington, repeated the historic reaction on the 28th, and on the same Saturday morning, workers at the Johns Hopkins Laboratory obtained the same results.

tuve.gif (69784 bytes)

Merle Antony Tuve

On January 26th of that year Bohr attended a Conference on Theoretical Physics at George Washington University in Washington, D.C. Atomic fission had electrified the many scientists gathered there. There was much discussion and speculation over this new phenomenon. Among the top-flight atomic artillerymen present was Enrico Fermi. He was now professor of physics at Columbia University. He had just arrived from fascist Italy, with his scientist wife, Laura, who had worked with him in some of his early experiments. When Mussolini embraced racism, Fermi, an antifascist, thought the time had finally arrived when he must leave his native country and try the free air of America. During his talk with Bohr, Fermi mentioned the possibility that nuclear fission might be the key to the release of colossal energy by the mechanism of a chain reaction. He speculated that the fission of the uranium atom might liberate additional neutrons which might be made to fission other atoms of uranium. In this way, there might be started a self-propagating reaction, each neutron released in turn disrupting another uranium atom just as one firecracker on a string sets off another firecracker until the whole string seems to go up like a torpedoed munition ship in one mighty explosion. Subatomic energy could thus be released and harnessed, producing from a single pound of uranium energy equivalent to that produced by 40,000,000 pounds of TNT.

That possibility was really something to think about. But nothing of this sort had, as yet, been seen in either Berlin or New York. Atomic energy of this order still remained fettered. Fermi at that moment may not have realized that there was the genesis of a profoundly disturbing drama.

Wheeler.jpg (5238 bytes)

John Archibald Wheeler

The possibility of a chain reaction still obsessed nuclear physicists. Why had not the chain reaction of uranium fission actually occurred? Niels Bohr and a former student, John Archibald Wheeler (1911-2008) of Princeton University, puzzled over this question. At a meeting of the American Physical Society at Columbia University on February 17, 1939, they advanced a theory of uranium fission which postulated that not all the uranium employed as target actually fissioned. They believed that less than one percent of their uranium target disintegrated because only one of the three isotopes of uranium was actually capable of fission. This fissionable isotope has an atomic weight of 235 instead of 238 which is the atomic weight of 99.3% of the uranium mixture found in nature. U-238 is extremely stable; its half-life has been estimated to be one hundred million years. It behaves like a wet blanket over U-235. (There is another isotope which has the atomic weight of 234. This is found in uranium only to the extent of a negligible 0.006%.) Isotopes, as you know, are atoms of the same element having the same atomic number (protons) and similar chemical properties, but differing in their atomic masses (neutrons).

Bohr and Wheeler reasoned that a chain reaction could be obtained only from pure U-235. They also proposed that the chain reaction could be initiated by bombardment with slow neutrons, and Fermi suggested that graphite could be used as the slowing-down agent or moderator. Neutrons normally emitted are very fast (10,000 miles per second). Such fast neutrons are easily captured by U-238, but no fission occurs. When forced to hurdle some retarding agent such as graphite or heavy water fast neutrons collide with it and lose some of their energy, which may slow down their speed to a pace no greater than 1 mile per second. The slow neutron may bounce around from one U-238 nucleus to another until it strikes the nucleus of a U-235 atom and splits it. The effectiveness of the slow or thermal neutron has been compared to the slow golf ball which rolls along slowly and drops gently into the cup on the green while the fast moving golf ball simply hops past the cup.

The first researcher to separate a minute quantity of U-235 from the isotope mixture of natural uranium was Alfred O. Nier (1911-1994) of the University of Minnesota. He sent this microscopic quantity of U-235 (about 0.02 micrograms) to Fermi and others at Columbia University. This bit of U-235 and another speck from the General Electric laboratory were bombarded with slow neutrons in the Columbia cyclotron and the prediction of Bohr and Wheeler was confirmed in March, 1940.

nier.jpg (11025 bytes)

Alfred Otto Carl Nier

Nier had worked hard and long to separate the tiny bit of U-235 by means of the mass spectrometer, but the process was extremely slow. At the rate at which he was separating U-235 from the rest of the mixture of uranium it would have taken 75,000 years to manufacture just one single pound of this key isotope. Thus the possibility of releasing huge quantities of atomic energy still remained a dream. Fantastic stories went the rounds to the effect that Hitler had ordered his scientists to redouble their efforts to supply him with several pounds of the powerful element whose terrific destructive powers would bring world domination for Nazi arms. But, for the moment, it continued to remain as devastating a secret weapon as the rest of his threats.

Nevertheless, a great deal of research in this field continued. In 1939, more than one hundred papers on nuclear experiments were published. But the consensus of expressed opinion was against any early solution of the problem. "I feel sure, nearly sure," Einstein had observed, "that it will not be possible to convert matter into energy for practical purposes for a long time." On February 2, 1939, Fermi delivered himself of the opinion that "whether the knowledge acquired of the possibility of a chain reaction will have a practical outcome, or whether it will remain limited to the field of pure science cannot at present be foretold." On his return from the Washington meeting of the American Physical Society, Fermi was asked on the radio how soon the world would blow up. He remained silent on this question. Eighteen months later the journal Electronics, summing up all the work published to that time, declared, "The matter stands at present waiting a conclusive demonstration that the chain reaction of U-235 is indeed a reality . . . . In the meantime U-235 is an isotope to watch. It may be going places."

price.jpg (11018 bytes)

Byron Price

But there was nothing for the general public to watch. In March 1939, Bohr returned to Denmark. A year later he and the American nuclear scientists voluntarily agreed not to publish any more of their findings in this explosive field. In June, 1943, Byron Price (1891-1981), Director of Censorship, sent a confidential note to 20,000 news outlets asking them "not to publish or broadcast any information whatever regarding war experiments involving production or utilization of atom smashing, atomic energy, atomic fission, atom splitting, or any of their equivalents, the use for military purposes of radium or radioactive materials, heavy water, high voltage discharges, equipment, cyclotrons, and the following elements or any of their compounds, namely, polonium, ytterbium, hafnium, protactinium, radium, rhenium, thorium, and deuterium."

Thus the security blackout of all U-235 news left the world speculating as to whether atomic energy could actually ever be harnessed for practical use. When the news of triumph finally came on August 6, 1945, it surprised even the most optimistic scientists. The great marvel, said President Truman, "is not the size of the enterprise, its secrecy or cost, but the achievement of scientific brains in putting together infinitely complex pieces of knowledge held by many men in different fields of science into a workable plan." The controlled release of atomic energy was not only the most spectacular but also the most revolutionary achievement in the whole history of science. Within the short span of five years a handful of scientists, standing on the shoulders of thousands of others who had been probing the heart of the atom for fifty years, uncorked a torrent of concentrated energy that can improve the world immeasurably or blot it out completely.

The manufacture of the atom bomb is another example of the oneness of pure and applied science. Out of the purely theoretical investigations relating to the composition and heat of the sun, the nature of radiation, and the structure of the atom came remarkable inventions such as the photoelectric cell or magic eye, television, and the electron microscope. Men who never dreamed of having a hand in the construction of a practical gadget were supplying concepts and mathematical equations which eventually made possible the most devilish war weapon ever dreamed up by man.

The thousands of scientists of every race, nationality, religion, and motivation had, except for the last chosen few, no idea of the monster they were fashioning. They knew only that they were adding just another bit to human knowledge. Science is an international activity. The widespread dissemination of the findings of researchers in hundreds of laboratories throughout the world makes possible the cooperation of all peoples in the hunt for new principles and new machines. Men and women from almost every corner of the earth played their parts in the drama of atomic energy. Only a very few of these actors were aware that, near the close of the drama, there would emerge an atomic bomb. William Roentgen (1845-1923), the German who discovered X-rays in 1895, could not have dreamed of it. The Frenchman, Henri Becquerel (1852-1908), who noticed the effect of the uranium ore, pitchblende, on a photographic plate in a darkroom, could not have guessed it. The Polish-born scientist, Marie Curie (1867-1934), caught a glimpse inside the spontaneously disintegrating world of the radium atom, but could not foresee the harnessing of subatomic energy. J.J.Thomson (1856-1940) of England and Ernest Rutherford (1871-1937) of New Zealand, who gave us the electron and the proton, considered controlled atomic energy both too expensive and to far distant.

roentgen.jpg (35035 bytes)

William Roentgen

becquerel.jpg (39652 bytes)

Henri Becquerel

mpcurie.jpg (53047 bytes)

Marie & Pierre Curie
1867-1934 & 1859-1906

JJThoms.gif (27718 bytes)

J.J. Thomson

rutherford.jpg (51228 bytes)

Ernest Rutherford

Scientists working in the field of nuclear physics included Niels Bohr, a Dane, Enrico Fermi, an Italian, Wolfgang Pauli (1900-1958), an Austrian, George Charles von Hevesy, also called George Charles de Hevesy (1885-1966), a Hungarian, Pjotr Leonidovich Kapitza (1894-1984) and Dmitri V. Skobeltsyn (1892-1990) of the Soviet Union, Sir Chandrasekhara Venkata Raman (1888-1970) of India, and Hideki Yukawa (1907-1981), a Japanese who as early as 1934 foreshadowed the presence of a new nuclear unit, the mesotron, which was later discovered by California Tech's Carl D. Anderson (1905-1991), son of a Swedish immigrant.

pauli.jpg (51206 bytes)

Wolfgang Pauli
hevesy.jpg (13902 bytes)

George Charles von Hevesy

kapitza.jpg (30497 bytes)

Pjotr L. Kapitza

skobeltsyn.gif (38333 bytes)

Dmitri V. Skobeltsyn

raman.jpg (39420 bytes)

Chandrasekhara V. Raman

yukawa.jpg (43991 bytes)

Hideki Yukawa

cdanderson.jpg (24005 bytes)

Carle D. Anderson

When the curtain that hid the work on atomic fission during the war was partially lifted after Hiroshima, a thrilling story was revealed. After the reality of atomic fission had been demonstrated early in 1939 and the possibility of a chain reaction had been partially proved in the spring of that year by Frederic Joliot and his collaborators in France, the whole world knew these results. Among those interested in this new milestone were, of course, several German nuclear physicists who saw the possibility of manufacturing a super-high explosive on the basis of the concentrated energy locked up in the heart of the atom's nucleus. There were two laboratories in Germany in 1939 capable of nuclear research. Neither of them had a cyclotron, but in the autumn of 1940 the first "pile" was set up at the Berlin-Dahlen consisting of layers of uranium oxide and paraffin. It failed. Hitler kept rattling his sword more and more menacingly over Europe, as his scientists continued their investigations.

smyth.jpg (53676 bytes)

Dr. Henry DeWolf Smyth

It was very different in the United States. "American-born nuclear Physicists," wrote Dr. Henry DeWolf Smyth (1898-1986) in the official Army Report on the Atomic Bomb released six days after Hiroshima, "were so unaccustomed to the idea of using their science for military purposes that they hardly realized what needed to be done. Consequently, the early efforts both restricting publication and getting government support were stimulated largely by a small group of foreign-born scientists in this country."

teller2.jpg (7912 bytes)

Edward Teller

weisskopf.jpg (10358 bytes)

Victor Frederick Weisskopf

pegram.jpg (18562 bytes)

George Braxton Pegram

The first of these scientists, who included Edward Teller (1908-2003) and Victor Frederick Weisskopf (1908-2002) was Enrico Fermi, who was put in touch with Navy officials by George Braxton Pegram (1876-1958), Dean of the Graduate Faculty of Columbia University, as early as March, 1940. The European-born scientist suggested to the Navy the possibility of producing terrific explosions with the aid of uranium and neutrons. The Navy showed interest.

szilard.jpg (14171 bytes)

Leo Szilard

Another refugee scientist working on atomic energy at this time was forty-year-old Leo Szilard (1898-1964), visiting experimental physicist at Columbia University. This Hungarian had served his native country in World War I, had continued his studies in Berlin, and then moved to England. On March 3, 1939, he and Walter Henry Zinn (1906-2000), a Canadian attached to the College of the City of New York, were working on the seventh floor of the Pupin Building of Columbia University.

wzinn.jpg (64684 bytes)

Walter H. Zinn

They were attempting to confirm the reality of atomic fission. They set up the necessary apparatus, turned a switch, watched the screen of a television tube for the telltale sign. "That night," wrote Szilard, "I knew that the world was headed for sorrow." After Hahn's epochal experiment, Szilard, a very active anti-Nazi, had come to the United States with some apparatus he had constructed in England to continue his experiments at Columbia. Szilard was seriously frightened by the implications of atomic fission. In September, 1939 the German Heereswaffenamt had organized a research group to examine its possibilities. It consisted of Walther Wilhelm Bothe (1891-1957), Hans Wilhelm Geiger (1882-1945), Otto Hahn, Paul Karl Maria Harteck (1902-1985), and Carl Friedrich von Weizsacker (1912-2007), son of the German Undersecretary of State. Suppose Hitler's scientists went to work in dead earnest to construct a bomb on the atomic energy principle? They might succeed and enslave the whole world! He rushed to Princeton to talk the matter over with his friend Eugene P. Wigner (1902-1995), who had come here from Hungary in 1930, and possibly with Einstein. (In 1937 Wigner had become an American citizen, and Szilard followed him in 1943.)

bothe.jpg (26167 bytes)

Walther Wilhelm Bothe

geiger.jpg (41412 bytes)

Hans Wilhelm Geiger

harteck.jpg (12398 bytes)

Paul Karl Maria Harteck

weizsacker.jpg (10009 bytes)

Carl Friedrich von Weizsacker

wigner.jpg (55794 bytes)

Eugene P. Wigner

Another American of foreign birth who was scared almost to distraction was Alexander Sachs (1893-1973). He had come here from Russia as a boy, had been educated at Harvard and Cambridge, had become informal economic adviser and industrial consultant to Franklin D. Roosevelt, who in 1933 had appointed him first chief economist and organizer of the NRA. Sachs agreed with Szilard that something had to be done quickly. He knew the tremendous prestige of Einstein. When the latter suggested that Sachs go to see Franklin D. Roosevelt, he lost no time. On October 11, 1939, he delivered a letter from Einstein to the President at the White House. Hitler's armies were already on the march. Poland had been crushed.

The letter read in part as follows:

"In the course of the last four months it has been made probable through the work of Joliot in France as well as Fermi and Szilard in America--that it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears this could be achieved in the immediate future".

"This new phenomenon would also lead to the construction of bombs, and it is conceivable--though much less curtain--that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port, together with some surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air."

Sachs reminded the President that Fermi, Szilard, and our American scientists were probably only one step ahead of the Nazi scientists. Germany had overridden Czechoslovakia, its precious uranium ores were in its hands; the most important source of uranium was the Belgian Congo, Belgium would undoubtedly be invaded by the German hordes, and this huge source of uranium would then be lost to the United States.

Roosevelt saw the danger at once. He had the vision and the courage to act promptly. He brushed aside those of his advisers who were hesitant and less alarmed. Hardly five weeks after World War II had broken out, President Roosevelt appointed an "Advisory Committee on Uranium." This committee consisted of Alexander Sachs, E.P. Wigner, Edward Teller of George Washington University, Fermi, Szilard, and several Army and Navy men. They met on October 21, 1939. The military men on the committee felt that the federal government should not engage in atomic energy experiments but should leave this work to the universities. In November of the same year the committee recommended getting four tons of graphite to be used as moderator and 50 tons of uranium oxide. The first appropriation, a pitifully tiny sum of $6000, was made for this purpose on February 20, 1940.

lawrence.jpg (55490 bytes)

Ernest Orlando Lawrence

In the meantime, Ernest Orlando Lawrence (1901-1958) had been awarded the Nobel Prize on December 10, 1939, for his development in 1932 of the cyclotron, the superb atom-smashing machine which he had, in the succeeding years, developed into a mighty tool for atomic fission work. This event served as a sharp reminder that others, too, had cyclotrons with which to carry out atomic fission experiments on a large scale. Early in 1940 Sachs and Einstein were dissatisfied with the snail-like progress of the uranium research. In April of that year Sachs was again at the White House pleading with Roosevelt for more haste and more money.

At this very moment England was getting nervous about the possibility of a German atom bomb. British scientists had learned that a large section of the Kaiser Wilhelm Institute had been set aside for nuclear research. They were now doing something to meet the crisis. A committee under the leadership of Nobel Prize winner Sir George P. Thomson (1892-1975), son of the discoverer of the electron, was appointed in April, 1940. It was first under the Air Ministry and later under the Ministry of Aircraft Production. The work was started by Robert O. Frisch (1904-1979) and Joseph Rotblat (1908-2005) at Liverpool, and later was extended to the famous Cavendish Laboratory of Experimental Physics under Norman Feather (1904-1978) and Egon Bretscher (1901-1973). French scientists, too, were aware of the danger of an atom bomb in the hands of the Nazis. When in June, 1940, France fell to Hitler, Frederic Joliot-Curie, codiscoverer of artificial radioactivity and a leader in the field of atom chain reaction, sent his collaborators, Hans von Halban (1908-1964) and Lew Kowarski (1907-1979), to Cambridge to aid in the work of the British atom scientists. Kowarski took with him the 165 quarts of heavy water which the French government had brought from Norway before its invasion. The French scientists, pioneers in the field of slow neutron bombardment, thought of using this heavy water as a moderator in the slowing down of neutrons. Joliot remained in France to become an active worker in the resistance movement in his country and to organize the manufacture of munitions for the underground patriots in Paris.

rotblat2.jpg (17123 bytes)

Joseph Rotblat

kowarski2.gif (14935 bytes)

Lew Kowarski

At the same time that French scientists were leaving for England, President Roosevelt in June, 1940, set up the National Defense Research Committee (NDRC), and the original Committee on Uranium became a subcommittee of this new body. Before the end of that year Columbia University received $40,000 for the study of a chain reaction. In the summer of 1941 Vanevar Bush (1890-1974), director of the NDRC, visited Roosevelt on the President's return from the Atlantic Charter meeting with Churchill. Bush gave Roosevelt a brief account of the work on atomic energy already under way and told him also of the reports which Kenneth Tompkins Bainbridge (1904-1996) and Charles Christian Lauritsen (1892-1968), who had attended meetings of Thomson's committee in England, had brought back.

bainbridge.jpg (16723 bytes)

Kenneth Tompkins Bainbridge

lauritsen.jpg (11820 bytes)

Charles Christian Lauritsen

attlee2.jpg (10325 bytes)

Clement Attlee

The British scientists by the summer of 1941 had definitely come to the conclusion that an atom bomb was feasible. Roosevelt then suggested to Clement Attlee (1883-1967), then a member of the Churchill cabinet, that the British scientists working on atomic energy pool their knowledge and efforts with those of our own scientists working on nuclear fission. This proposal was eagerly accepted by the Churchill government.

urey.gif (8716 bytes)

Harold C. Urey

Harold C. Urey (1893-1981), discoverer of heavy hydrogen, and George Braxton Pegram, physicist of Columbia University, were sent abroad in November, 1941, to confer with the British scientists. Just two months before, Churchill had asked Sir John August Anderson (1876-1959) to supervise the work of an atom bomb project, and the latter had brought together England's ace atom scientists, including Sir Charles Galton Darwin (1887-1962), member of the fourth generation of Darwin's family; John Douglas Cockcroft, Sir Marcus Lawrence Oliphant (1901-2000), Norman Feather (1904-1978) of Cambridge, first to split the oxygen atom, and two refugee scientists, Sir Rudolph Ernst Peierls (1907-1995), Professor of Applied Mathematics at the University of Birmingham since 1937, and Sir Francis (Franz) Eugen Simon (1893-1956), reader in thermodynamics at Oxford since 1933.

jaanderson.gif (7983 bytes)

Sir John August Anderson
cgdarwin.jpg (3467 bytes)

Sir Charles Galton Darwin
oliphant2.jpg (5913 bytes)

Sir Marcus Lawrence Oliphant

peierls.jpg (11887 bytes)

Sir Rudolph Ernst Peierls

fesimon.jpg (14547 bytes)

Sir Francis (Franz) Eugen Simon

Sir James Chadwick (1891-1974), discoverer of the neutron and also a member of this original group, was terribly worried. During the summer of that year the Germans were experimenting in Leipzig with a small uranium pile using heavy water as a moderator. Their results were cloaked in secrecy. Werner Karl Heisenberg (1901-1976), top German nuclear physicist and one of the world's greatest authorities in this field, was believed to be directing this work.

chadwick.jpg (23882 bytes)

Sir James Chadwick

heisenb.jpg (67852 bytes)

Werner Karl Heisenberg

Urey returned to the United States in the week that terminated in Pearl Harbor Sunday. He shared the anxiety of Chadwick and brought home a sense of the utmost urgency. Heisenberg, on Feb. 26, 1942, had told Rust, German Minister of Education that "an atomic bomb could be produced in the pile on theoretical grounds." At this moment American and German scientists had arrived at similar results if we exclude our great success in isotope separation. What if the German scientists got the jump on us and the German High Command had agreed on an all-out effort to make atom bombs? This was altogether possible, for on November 6, only a month before, the NDRC had reported that "a fission bomb of superlatively destructive power results from bringing quickly together a sufficient mass of U-235. . . If all possible effort is spent on the program, we might expect fission bombs to be available in significant quantities within three or four years."

Things now began to move much faster. Just a day before the attack on Pearl Harbor an "all-out effort" to manufacture the atom bomb was finally decided upon. Eleven days later the NDRC was reorganized under the Office of Scientific Research and Development (OSRD) headed by Vanevar Bush. A delegation of British scientists, including Peierls, Simon, and Halban, came to the United States to help in the coordination of the work. Finally, on August 14, 1942, the Manhattan Engineer District project was started by order of Secretary of War Henry Lewis Stimson (1867-1950). Major-General Leslie Richard Groves (1896-1970), forty-two-year-old army construction engineer, a West Pointer, was made director of all army activities relating to the project. Dr. Richard Chace Tolman (1881-1948), dean of the graduate school of the California Institute of Technology, was made his scientific advisor.

stimson.jpg (5952 bytes)

Henry Lewis Stimson

groves.jpg (19167 bytes)

Leslie Richard Groves

Long before this step had been taken, various research groups had already been assigned to several crucial problems. One of these was the production of a controlled and self-maintaining nuclear chain reaction. As early as January, 1942, it was decided to concentrate this project at the University of Chicago where Arthur Holly Compton (1892-1962) was working with neutrons. Fermi's group working at Columbia, a number of scientists working at Princeton University, and several other researchers came to Chicago to team up in what became known as the Metallurgical Laboratory.

compton.jpg (41146 bytes)

Arthur Holly Compton

One of the essentials of this project was a good supply of pure uranium of which only a few pounds were actually available in 1941. There was plenty of the impure uranium ore obtainable from the Belgian Congo, and from the Eldorado pitchblende mines of the Canadian arctic wilds which had been taken over by Canada during the war. Getting the pure uranium metal from these ores was no simple matter. The first supply was delivered to the Chicago pile operators early in 1942. It came from a long wooden shed of the Iowa State College at Ames, where formerly coeds practiced archery. Here Dr. Frank Harold Spedding (1902-1984) of the chemistry department supervised the purification of the uranium which was to be used for nuclear fission. At this time Arthur Compton also called upon Harvey C. Rentschler (?-?) to make three tons of the metal for the Metallurgical Laboratory. Rentschler had worked with this metal at the Westinghouse Research laboratories in connection with electric lamp filaments, and had been supplying college laboratories with small amounts of this element for research. Rentschler got to work at once and before long had stepped up his yield from half a pound to 500 pounds daily. And instead of uranium costing $1000 per pound he pushed its production cost down to only $22 per pound.

spedding.jpg (9234 bytes)

Dr. Frank Harold Spedding

rentschler.jpg (102102 bytes)

Harvey C. Rentschler

A large doorknob-shaped structure called a pile was set up by Fermi on the floor of the squash-rackets court underneath the west stands of Stagg Field of the University of Chicago. The pile contained 12,400 pounds of specially purified graphite bricks with holes at calculated distances in which were embedded lumps of uranium oxide and pure uranium sealed in aluminum cans to protect the uranium from corrosion by the cooling water pumped through the pile. The bricks were arrayed in the form of a cubic lattice as suggested by Fermi and Szilard. The lattice structure was found to be the most effective arrangement of material for the slowing down of neutrons. The graphite bricks act as a moderator, to change fast neutrons into slow or thermal neutrons. The thermal neutrons produced then cause fission in U-235, producing a new generation of fast neutrons similar to the previous generation. Thus neutron absorption in U-235 maintains the chain reaction as a further source of neutrons.

A chain reaction will not maintain itself if more neutrons are lost then are produced. Just as coal will not continue to burn and the fire will be extinguished when the heat it generates is lost faster than it generates new heat, so U-235 will not fission so long as it loses neutrons faster than it generates them by fission. Neutrons may be lost by being absorbed either by U-238 or by impurities present in the uranium or in the graphite. U-238 absorbs neutrons but does not fission, hence these neutrons may be considered as lost. By careful purification of uranium and graphite, proper spacing of target and moderator to cut down the size of the pile, the chain reaction should, theoretically at least, be kept under control. That was the job assigned to Fermi and his assistant.

hlanderson.jpg (13342 bytes)

Herbert Lawrence Anderson

There was a great deal of theorizing, calculating, discussing, and changing of plans. There was a great deal, too, of piling and repiling of graphite bricks, hence the name pile for the uranium reactor. On the final day of trial Fermi, Compton, Zinn, and Herbert Lawrence Anderson (1914-1988) stood in front of the control panel located on a balcony ten feet above the floor of the court. Here stood George L. Weil (1908-1995), who was to handle the final control rod which held the reaction in check until it was withdrawn the proper distance. Another safety rod, automatically controlled, was placed in the center of the pile and operated by two electric motors which responded to an ionizing chamber. When a dangerously high number of neutrons were escaping, the gas in the ionizing chamber would become highly electrified. This would automatically set the motor operating to shoot a neutron-absorbing, cadmium-plated steel rod into the pile. As an added precaution an emergency safety rod call Zip was withdrawn from the pile and tied by a rope to the balcony. Horace Van Norman Hilberry (?-1986) stood ready to cut this rope if the automatic rods failed for any reason. Finally, a liquid control squad stood on a platform above the pile trained and ready to flood the whole pile with water containing a cadmium salt in solution.

120246.gif (158802 bytes)

The fourth anniversary reunion on the steps of Eckhart Hall at the University of Chicago, Dec. 2, 1946. Back row, left to right: Norman Hilberry, Samuel Allison, Thomas Brill, Robert Nobles, Warren Nyer and Marvin Wilkening. Middle row: Harold Agnew, William Sturm, Harold Lichtenberger, Leona W. Marshall and Leo Szilard. Front row: Enrico Fermi, Walter Zinn, Albert Wattenberg and Herbert Anderson.

Fermi started the test at 9:54 am by ordering the control rods withdrawn. Six minutes later Zinn withdrew Zip by hand and tied it to the rail of the balcony. At 10:37 Fermi, still tensely watching the control board, ordered Weil to pull out the vernier control rod thirteen feet. Half an hour passed and the automatic safety rod was withdrawn and set. The clicking in the Geiger counter grew faster and the air more tense. "I'm hungry. Let's go to lunch," said Fermi, and his staff eased off to return to the pile at 2 o'clock in the afternoon. More adjustments, more orders, and at 3:21 Fermi computed the rate of rise of neutron count. Then suddenly, quietly, and visibly pleased, Fermi remarked, "the reaction is self-sustaining. The curve is exponential." Then for 28 more minutes the pile was allowed to operate. At 3:54 P.M. Fermi called "OK" to Zinn, and the rod was pushed into the pile. The counters slowed down. It was over. The job that came close to being a miracle was completed. December 2, 1942 marked the first time in history that men had initiated a successful, self-sustaining nuclear chain reaction. Only a handful of men surrounding Enrico Fermi knew that on this wintry Wednesday afternoon mankind had turned another crucial corner.

conant.gif (18290 bytes)

Dr. James Bryant Conant

Arthur H. Compton had witnessed this successful achievement and put through a long distance telephone call to Dr. James Bryant Conant (1893-1978), who was in charge of the project for OSRD. "The Italian navigator has landed in the New World. It is a smaller world than he believed it was," said Compton to Conant. To Conant the "smaller world," though no code had been prearranged, meant that the atomic pile was smaller and its fires were not as violent as had been expected. Conant then asked, "Are the natives friendly?" Compton took this to mean whether he was ready to go ahead full blast. The answer to that query was "Yes, very friendly," and Fermi and his Chicago group lost no time in following through.

Working with this uranium pile partly shrouded in balloon cloth to keep out neutron-absorbing air was a most dangerous business. Death and destruction threatened at almost every move. A chain reaction might get out of control and produce a super-explosion that could blast the researchers into kingdom come. And there were thousands of other people who stood in imminent danger of being crippled by atomic fission. People living near the university might have been blown to vapor one fine morning had not the men at the pile taken every conceivable precaution--and been lucky, too. It had been anticipated that the nuclear reaction would start from spontaneous fission caused by a stray neutron or other source (such as bombardment from a wandering cosmic ray) just as soon as the pile reached a certain size, known as the critical size. This condition is reached when the number of free fission neutrons just equals the loss of neutrons due to non-fission capture and escape from the surface. Since the rapid loss of neutrons into the surrounding space is a surface phenomenon, and nuclear fission of U-235 is a volume effect, it would be disastrous to build a pile so large that the number of neutrons produced by fission would be greater than the number of neutrons lost by non-fission capture and by escape from the surface of the pile. Such a pile would produce an uncontrolled fission chain reaction explosion. The critical size of the pile under construction had been calculated from all the available data, and it turned out that an error had actually been made, for the approach to critical size was later found to occur at an earlier stage of assembly than had been anticipated. Of course, Fermi and his men, working in a not too familiar field, had taken every conceivable precaution. "This was fortunate," wrote Dr. Smyth, and these three words must remain one of the classic understatements in the long history of the hazards of scientific discovery.

If the men at the pile escaped sudden death, they might have still succumbed to slow, painful destruction caused by the penetrating rays and poisonous radioactive particles emitted during nuclear fission. As a safeguard against the perils of such penetrating radiation and poisons, the pile was shielded very carefully by 5-foot-thick walls of absorbent material. No one dared come within reach of the pile, and manipulations had to be performed by ingenious devices permitting remote control.

The original purpose of the Metallurgical Laboratory project was the creation of a large and easily controlled chain reaction. This objective was achieved. In addition, however, the pile turned out to be a plant which efficiently manufactured a new element in large quantities. This element is plutonium. It is a brand new man-made chemical element which fissions just as easily as U-235. The story of the birth of this synthetic element goes back to a day in May, 1940, when two men using Lawrence's cyclotron at Berkeley, California, bombarded uranium with neutron bullets. The two men were Edwin Mattison McMillan (1907-1991) and Philip H. Abelson (1913-2004), who was later decorated by our government for this achievement. After the bombardment of U-235 they detected traces of a new element, heavier than uranium. This new element, No. 93, was named neptunium by McMillan. It was a very difficult element to study, for its life span was very short. It threw out neutrons almost immediately and in a split second's time was no longer neptunium.

mcmillan2.gif (12282 bytes)

Edwin Mattison McMillan

abelson.jpg (8193 bytes)

Philip H. Abelson

It was exciting enough to have made a new element, but what was even more thrilling was the discovery, before the end of that same year, of still another element which turned out to be even more interesting than neptunium. McMillan, Glenn Theodore Seaborg (1912-1999), Arthur C. Wahl (1917-2006), and Joseph William Kennedy (1917-1957) learned late in 1940 that neptunium actually changed into another element. This fairly stable element, No. 94, was sensitive to neutron bombardment and fissioned in a similar manner to U-235, emitting other neutrons capable of producing a chain reaction. This was a tremendously important fact, for here science had a substance which could be used instead of U-235 in a projected atom bomb. Furthermore, this new element, plutonium, could be separated from natural uranium much more easily than could U-235. This was true because it is an entirely different element and could be separated by chemical means rather than by the very difficult physical means necessary for separating the isotopes of uranium.

seaborg.jpg (14780 bytes)

Glenn Theodore Seaborg

wahl.jpg (5268 bytes)

Arthur C. Wahl

Occasionally, when an atom of Uranium-238 is exposed to neutron radiation, its nucleus will capture a neutron, changing it to Uranium-239.  Uranium-239 has a half-life of about 23.45 minutes and undergoes beta decay into Neptunium-239.  Neptunium-239 has a half-life of about 2.4 days and decays into Plutonium-239 following a beta decay. 

Fission activity is relatively rare, so even after significant exposure, the Pu-239 is still mixed with a great deal of Uranium-238 (and possibly other isotopes of uranium), oxygen, other components of the original material, and fission products.  The Pu-239 can then be chemically separated from the rest of the material to yield high-purity Pu-239 metal.

The nuclear reactions involved in the discovery of neptunium and plutonium, and in the fission of the latter element, may be represented by the following steps:

238U + (neutron, gamma) 239U -(beta) 239Np -(beta) 239Pu
92+ 92+ 93+ 94+
146n 147n 146n 145n
Half Life = 4.47 x 109 a Half Life = 23.45 minutes Half Life = 2.4 days Half Life =24,110 a

summarized as:

238U (n, gamma) 239U -(beta) 239Np -(beta) 239Pu

If this newly discovered plutonium was to be manufactured on a scale large enough to meet the needs of the Manhattan District project, more of its chemical properties would have to be known. At the beginning the men at the Metallurgical Laboratory had only a trace of the element to work with and made some preliminary investigations of its properties by a tracer technique. Because of the radioactive nature of the element it was possible to gather some information of its behavior by mixing it with other elements and compounds.

A larger sample of the element, an amount that could be seen, was needed if further information vital to the whole project was to be obtained. The big cyclotrons of Lawrence's laboratory at Berkeley, California, and of Washington University of St. Louis went to work bombarding uranium with neutrons. For weeks the big machines were kept operating until as much as one-thousandth of a single gram of the element had been collected, enough for direct observation. Years before, chemists had developed a branch of analysis called microchemistry which could handle tiny amounts of chemicals weighing as little as 0.001 gram. But not even such a tiny bit of plutonium was available. So the chemists at the University of Chicago under Glenn Seaborg began in April, 1942, to develop a new method which could handle chemicals which weighed no more than 500 micrograms (1 microgram equals one-millionth of a gram) or about 1/5000 the weight of a single dime. (A human breath weights 750,000 micrograms.) This method is known as ultra-microchemistry. Midget test tubes called microcones were used. Ingenious devices were invented to handle these minute quantities of chemicals, and very clever methods were introduced to safeguard the health of the men handling these radioactive substances. Finally 2.77 micrograms of the first pure chemical compound of plutonium was prepared by Burris Bell Cunningham (1912-1971) and Louis B.Werner (1921-2007) at the Metallurgical Laboratory at the University of Chicago on August 18, 1942. "This memorable day will go down in scientific history," wrote Seaborg, codiscoverer of plutonium, "to mark the first sight of a synthetic element, and, in fact, the first isolation of a weighable amount of an artificially produced isotope of any element."

werner.jpg (7389 bytes)

Louis B. Werner

werner_cunningham.jpg (16461 bytes)

Louis B. Werner & Burris Bell Cunningham
1921-2007 & 1912-1971

  The first self-sustaining chain reaction had been achieved in December, 1942, only three months after the first weighable amount of plutonium compound had been prepared and studied. A third major problem in the preliminary work of Manhattan District was also well on its way to solution. This was the preparation of pure U-235, the first fissionable substance then known. Nier had first separated this isotope from natural uranium, but his method was so slow and laborious that it would have taken a scientist several thousand years to separate a single gram of pure U-235. Better and faster methods of separating the precious U-235 had to be devised. Several methods had been suggested and tried as far back as 1939. The electromagnetic method, first employed by Francis W. Aston (1877-1945) in 1919, was being used by Lawrence at the University of California. This consisted of shooting ionized gaseous particles of a uranium compound through an electric field which accelerated them to a speed of several thousand miles a second. They then entered a strong field between the poles of a powerful electromagnet which curved them into a circular path. Molecules of the lighter isotope (U-235), being bent more than those of the heavier isotope (U-238), could thus be separated, and the pure U-235 trapped. Lawrence used the huge electromagnet of his dismantled 37-inch cyclotron for this job. The huge electromagnet machine employed by him in preparing pure U-235 was named the calutron from the two words California and cyclotron.

aston.gif (11601 bytes)

Francis W. Aston

A second method, known as the gaseous diffusion method, was used by Harold C. Urey and John R. Dunning at Columbia University. Urey had had considerable experience in separating the isotopes of hydrogen by this method and developed it further for this most pressing need. The diffusion method consists of passing a gaseous uranium compound (fiercely corroding uranium hexafluoride, UF6) through barriers of very fine filters. The lighter vapor passed through filters faster than the heavier vapor, and thus by a continuous process a complete separation of U-235 from the other isotopes of natural uranium was effected. Both of these methods, as well as two others--thermal diffusion and centrifugal--were tried. The thermal diffusion method depends upon the fact that if there is a temperature difference in a vessel containing a mixed gas, one gas will concentrate in the cold region and the other gas in the hot region. All of these methods were slow, laborious, at times disappointing and discouraging. But new tricks were devised, new improvements were introduced, and new information was gathered during this long period of preliminary investigation.

Much of the preliminary work had now been completed by hundreds of scientists in dozens of laboratories around the country. More than 30 volumes of reports had been written. It was decided to go into large-scale production of both U-235 and plutonium for the making of atomic bombs. A bold step had to be taken. Instead of setting up a small pilot plant to test final manufacturing procedures, it was necessary to jump at once into large-scale production. "In peacetime," wrote Smyth, "no engineer or scientist in his right mind would consider making such a magnification in a single step." But there was no alternative. The Nazis were thought to be working on an atomic bomb. At the Norsk Hydro Company plant at Vermork near Rjukan, Norway, the Germans were already producing several hundred liters of "heavy water" to be used in slowing down neutrons. This was considered such a threat to us that the Allies with the help of Norwegian patriots decided to put the plant out of commission. In the fall of 1942 five Norwegians were parachuted from a British plane near the plant and awaited four others who came later. Under the leadership of the daring 26-year-old Sverre Haugen (?-?), the patriots succeeded in blowing up the heavy water apparatus. Two more attacks were made on it by commandos during the winter of 1942 and the spring of 1943, but the plant was repaired. Finally, on November 16, 1943, Flying Fortresses and Liberators of the U.S. Bomber Command attacked, and the Germans decided to dismantle the plant and send the heavy water and machinery to Germany. Norwegian patriots blew up the ferryboat carrying the heavy water in February of the following year.

The Germans were actually spending very little money on atomic-bomb work. Heisenberg revealed this in an article in Nature in 1947. In the early part of 1942 he had tried to get some of the top flight Nazis to a luncheon for the purpose of getting more help. Fortunately for us, he failed. The Germans expected a quick victory and thought a successful bomb project would take at least twenty years. In addition, the Germans were blinded by belief in their own superiority; many of their scientists, selected for political reasons rather than for their scientific abilities, had a contempt for so-called non-Aryan science. Nevertheless, they tried to get information about our own atom-bomb program. They knew that Niels Bohr would be valuable to the Allies. Hitler issued an order for the capture of the Danish scientist, who was working in Denmark at that time. The Danish underground learned about this, and smuggled Bohr and his family and Georg von Hevesy out of the country in a fishing boat which landed them in Sweden. Bohr was still not safe, and 19 days later a British Mosquito bomber picked him up for a flight to England. Because of fear that the Germans might intercept the plane, the pilot was instructed to drop Bohr by parachute through the bomb bay should his plane be attacked. Bohr almost died during the flight. As the plane rose into high altitudes the pilot instructed him to put on his oxygen mask. But Bohr did not get the warning, for he was not wearing his earphones which were too small for his rather large head. He became unconscious but fortunately recovered when the plane came down to lower altitudes.

The Nazis also sent spies to the United States to get information about our atom bomb plans. At least five of these German spies reached the country but they were all intercepted, and American alertness prevented any of our secrets being revealed or any sabotage being committed in our uranium plants.

In December, 1942, it was decided to proceed at once to the manufacture of sufficient quantities of both U-235 and plutonium to be used in atomic bombs. This meant increasing the available amounts of these elements many millions of times. It meant amplifying the ultra microchemistry of the Metallurgical Laboratory workers a billion times or more. It meant operating several huge uranium piles in plants designed from data collected during experiments with almost gossamer bits of plutonium. It meant constructing entire cities of many massive concrete structures to perform the colossal tasks ahead. Two sites were chosen and three plants were to be constructed.

One of these sites was Oak Ridge, Tennessee, near Knoxville. Here, early in 1943, the duPont Company built a plant at the Clinton Engineer Works site, including an air-cooled uranium-graphite pile which was to manufacture plutonium. This pile was started in November of that year and within two months the first batch of plutonium, less than 1/5 gram, was delivered. It had come at the end of a long process of separation from the uranium from which it had been formed during the chain reaction initiated in the pile. Uranium slugs, after exposure in the pile, were transferred under water to hermetically sealed rooms surrounded by thick walls of concrete, steel and other absorbent material. Several of these cells, two-thirds buried in the ground, formed a continuous fortresslike, almost windowless structure, 100 feet long, called a canyon. The plutonium-rich uranium rods were passed along from one cell to another, chemically treated until all of the plutonium was separated from the uranium. All of these operations were performed by remote control because of the hazards to health and even life caused by the radioactive products of nuclear fission that included not only neutrons, penetrating radiation similar to X-rays, but also dozens of radioactive isotopes such as iodine and xenon.

A second plant was erected at Oak Ridge where pure U-235 was manufactured by separation from natural uranium by the electromagnetic method developed by Lawrence. Mammoth electromagnets, 250 feet long, containing thousands of tons of special steel were employed. The pull of these magnets on the nails in the shoes of workers in this plant made walking difficult. Another plant using the gaseous diffusion method developed by Urey was built by the Chrysler Corporation. It consisted of sixty-three buildings. A thermal diffusion plant was also built here.

The other site selected was on the Columbia River near the Grand Coulee Dam. It was known as the Hanford Engineer Works and located in an isolated region near Pasco, Washington. Construction started in 1943, and the job was completed in record time. Its first large water-cooled pile for the manufacture of plutonium was built by duPont and went into operation in September, 1944. By the summer of the next year, just before the war ended, the entire plant was humming. All of its three piles, located several miles apart for safety, were heating the waters of the Columbia River. During the operation of a pile a large amount of heat is produced by atomic fission. The pile is cooled by water, which at the Hanford plant came from the Columbia River in volumes estimated to be big enough to supply a large city. The cold water of the Columbia River was first filtered, then treated before it was circulated through the pile.

Sixty thousand workers and their families, sworn to the strictest secrecy, poured into Richland and the Hanford area. Out of a barren wasteland, a city which became the fourth largest in the state sprang up almost overnight--a city whose name had never even appeared on a map. The story of Oak Ridge was equally amazing. Oak Ridge did not exist in 1941. Within a short time farms and forests became a city of 75,000 people, the fifth largest city in Tennessee. At the peak of the Manhattan project 125,000 people were engaged, including 12,000 college graduates.

The radioactivity of a single pile was estimated to be equal to that of a million pounds of radium. Hence the health of the scientists, engineers and other workers had to be constantly and carefully watched. The white-blood-corpuscle count was used as the main criterion as to whether a person was suffering from overexposure to radiation. Men carried small, fountain-pen-shaped electroscopes in their pockets to indicate the extent of exposure to dangerous fission products. Later a small piece of film was placed in the back of every worker's identification badge. The film was periodically developed for signs of blackening, indicating exposure to radiation. Contamination of laboratory furniture and equipment by alpha rays was charted by another specially constructed instrument, euphemistically called Pluto, for the god of the underworld. Geiger counters were used to check contamination of almost everything, including mops and laboratory coats, before and after laundering. No person whose clothes, hair, or skin was contaminated by even traces of radioactive material could get by the exit gates of certain laboratories without being detected, for concealed in these gates were instruments which sounded an alarm. The water which left the factories was constantly analyzed for radioactive material, and the dust of the air was checked by another instrument, called "sneezy." Factory stacks were built high enough to insure adequate dispersion of gases, dust, and vapors.

Even before the mammoth plants at Hanford and Clinton had been completely designed, an atomic bomb laboratory was erected on an isolated mesa 7000 feet above sea level near Los Alamos, New Mexico, twenty miles from Santa Fe. At the foot of this mesa were the ruined cliff dwellings and mud huts of the Pueblo Indians. A winding mountain road led to the top of the mesa. Here, in what was once a boys' ranch school, almost completely hidden from the rest of the world, for safety and security, the first atom bomb was to be constructed. To this spot, which was soon to become the best equipped physics laboratory in the world, a young man in his late thirties was called from the University of California. This scientist was the gifted, versatile, and brilliant theoretical physicist Julius Robert Oppenheimer (1904-1967), a New Yorker and graduate of Harvard University. "Oppy," as he was known to his many friends, was placed in charge of this laboratory, where he arrived in March 1943. With tremendous energy, superb organizing ability, an uncanny insight into the multitude of problems confronting the project, and great personal charm Oppenheimer soon turned Los Alamos into a marvelous workshop staffed by the best brains in atomic physics. Samuel King Allison (1900-1965) of the University of Chicago was his right-hand man.

oppenheimer.jpg (9691 bytes)

Julius Robert Oppenheimer

allison.jpg (7273 bytes)

Samuel King Allison

einst_op.jpg (89088 bytes)

Albert Einstein & Julius Robert Oppenheimer

Machines were soon installed. A cyclotron from Harvard, two Van de Graaff electrostatic generators from Wisconsin, a Cockcroft-Walton high voltage device from the University of Illinois, and a thousand and one other contraptions were made ready for the crucial experiment. Men were assigned to their tasks and frequent consultations were called to decide upon ticklish problems as they arose from time to time. The men who worked at Los Alamos or were consulted included the American Nobel Prize winners in physics and chemistry-- Carl D. Anderson, Arthur H. Compton, Clinton Joseph Davisson (1881-1958), Albert Einstein, Irving Langmuir (1881-1957), Ernest O. Lawrence, Robert Andrews Millikan (1868-1953), Isidor I. Rabi (1898-1988), Otto Stern (1888-1969), and Harold C. Urey. Here, too, Niels Bohr (alias Mr. Nicholas Baker), who had eluded the Gestapo, was flown from England to help in the work. James Chadwick, discoverer of the neutron. Hans Albrecht Bethe (1906-2005) of Cornell University, originator of the hydrogen-helium nuclear change to account for the sun's heat, Robert Fox Bacher (1905-2004) of Cornell, Russian-born George Bogdan Kistiakowsky (1900-1982) of Harvard, Enrico Fermi, and several other refugee scientists pooled their knowledge in the final problem of constructing an atomic bomb.

davisson.jpg (23396 bytes)

Clinton Joseph Davisson

lang2a.jpg (12612 bytes)

Irving Langmuir

millikan.jpg (53708 bytes)

Robert Andrews Millikan

rabi.jpg (45528 bytes)

Isidor I. Rabi

stern.jpg (21440 bytes)

Otto Stern

bethe2.jpg (13710 bytes)

Hans Albrecht Bethe

bacher.jpg (3213 bytes)

Robert Fox Bacher

kistiakowsky.jpg (9230 bytes)

George Bogdan Kistiakowsky

The first experiments were begun at Los Alamos in July, 1943. Arthur H. Compton at Chicago had bet James Bryant Conant that he would deliver the first major batch of pure plutonium to Oppenheimer in New Mexico on a specific date. The stake was a champagne supper for the members of the old executive committee of the uranium project. The plutonium for the atom bomb was actually delivered a month later and the bet was paid off.

More and more plutonium and pure U-235 arrived at Los Alamos. It was known by this time that a chain reaction would not complete itself unless the fissionable material reached a certain minimum size known as the critical size. To prevent premature detonation of the bomb, therefore, several pieces instead of a single lump of U-235 and plutonium were used. The pieces could be brought together suddenly to form a large mass of critical size by shooting one fragment from a gun as a projectile against another piece as target. When the pieces met to form one single piece of critical size, the whole mass would explode in a split second. To reduce the critical size of the bomb, a covering which reflects neutrons back was used. This envelope is called a tamper.

That the scientists in the mesa laboratory did their job well was known to a handful of men who in rain and lightning witnessed the first explosion of an atomic bomb. This test explosion took place at 5:30 am, July 16, 1945, at the Alamogordo Air Base in a desert of New Mexico, 120 miles southeast of Albuquerque. The bomb, containing (according to the Smyth Report) between 4 and 22 pounds of plutonium and U-235 (a British report gave the weight as between 22 and 66 pounds), fissioned with a blinding glare, vaporized the steel tower on which it had been exploded, and left a crater half a mile in diameter covered with sand sintered to a green, glassy consistency. It was estimated that a temperature as high as 100,000,000oF was reached in the center of the explosion. The age of nucleonics was here.

Finally, the whole world learned about the new terror fashioned by science when at 8:15 AM Monday, August 6, 1945, a single uranium filled atom bomb nicknamed "Little Boy" dropped through the open bomb bay of the Enola Gay from an altitude of 31,600 feet wiping out the city of Hiroshima (pop. 240,000) precisely 47 seconds later killing 75,000 people. The bomb had been carried in a B-29 piloted by Colonel Paul W. Tibbets, Jr. (1915-Present). To avoid the possibility of premature detonation, an accident which would have wiped out all life on Tinian Island from which the plane took off, the bomb was not assembled until the plane was in the air and at a safe distance from the island. Captain William Sterling Parsons (1901-1953) assembled the atom bomb with its deadly plutonium or U-235 or both.

pwtibbets.jpg (9436 bytes) enolagay.gif (8289 bytes)
Col. Paul Warfield Tibbets, Jr.
February 23, 1915 - November 1, 2007

parsons.jpg (17328 bytes)

Captain William Sterling Parsons
November 26, 1901 - December 5, 1953

Since there was still no official reaction from Japan, the Americans felt there was no alternative but to prepare a second atomic attack.  The Hanford, WA plutonium bomb "Fat Man" was loaded into a B-29 known as Bock's Car named after its commander, Capt. Frederick C. Bock (1918-2000).

bockscar.jpg (14372 bytes)

Bock's Car

However, on this mission, the aircraft was flown by Major Charles W. Sweeney (1919-2004), with Capt. Bock flying one of the observation planes.  The primary target was to be Kokura Arsenal, with Nagasaki as the alternative.  Bock's Car took off on August 9, with "Fat Man" on board. This time, the primary target of Kokura was obscured by dense smoke left over from the earlier B-29 raid on nearby Yawata, and the bombardier could not pinpoint the specified aiming point despite three separate runs. So Sweeney turned to the secondary target, Nagasaki. There were clouds over Nagasaki as well, and a couple of runs over the target had to be made before the bombardier could find an opening in the clouds. At 11:00 AM "Fat Man" was released from the aircraft and the bomb exploded. The yield was estimated at 22 kilotons. Approximately 35,000 people died at Nagasaki in the immediate blast.

sweeney2.jpg (10826 bytes)
Major Charles W. Sweeney
December 27, 1919 - July 16, 2004

The objective of Manhattan District project had been reached. Never before in the history of man had such a colossal task been completed in so short a time. A heritage of scientific brains unsurpassed in the annals of theoretical science, a reservoir of brilliant engineering and industrial talent, a life-and-death situation that compelled planned, coordinated, and accelerated action, and finally an expenditure of two billion dollars made this epochal achievement possible. The long search for the key to some of the energy locked up in the heart of the atom was ended. The goal of the ancient alchemists had not only been reached but had been left far behind. And in this triumph, modern man had created a new problem for himself, a problem as challenging as the bomb itself--the problem of survival in a world which might be foolish enough to remain divided into hostile camps. This is the life-and-death problem raised by science and capable of solution by scientists and other men of good sense and good will.

bohr20.jpg (108568 bytes)

Stern, Lenz, Franck, Ladenburg, Knipping, Bohr, Wagner, von Baeyer, Hahn, von Hevesy, Meitner, Westphal, Geiger, Hertz, Pringsheim

berliner.jpg (115899 bytes)

Einstein, Franck, Haber, Hahn, Hertz

goetting.jpg (71316 bytes)

Reich, Born, Franck, Pohl

Copyright July, 1997 James R. Fromm Revised November, 2008