An Atomic History Chapter 1

Home , Discovery of the neutron, James Chadwick, Leo Szilard, Max Planck

An Atomic History 0-3 8/11/02 7:30 AM Page 6

Chapter One 7 Between 1898 and 1911, this work was continued by Ernest Rutherford, who studied the nature of the radiation emitted by uranium and thorium. Rutherford was the first to discover and name alpha and beta radiation, and link them with Thompson’s electrons. Rutherford also discovered that radioactive elements, whether they were uranium, thorium, or radium, would all spontaneously disintegrate by emitting alpha and beta particles. The 1 Nuclear Awakenings longevity of these elements was determined in "half-lives."6 Albert Einstein not only provided more pieces of the puzzle; he put the puzzle in a new frame. In 1905, while working in the Swiss Patent Office, Einstein prepared five papers on the nature of modern physics, any one of which would have secured his fame. One of the five, and the one for which he later received a Nobel Prize, dealt with the "pho- toelectric effect." In it, Einstein theorized that light is made of discrete packets or "quan- ta," and that the energy of each packet is determined by the wavelength of the light, not its intensity. Two of the five papers dealt with new evidence for the existence and size of atoms and molecules. Another two expounded a radical new theory on the relationship of The work done at the Savannah River Site is the culmination of over a hundred time and space: one dealt with the theory of relativity, while the other posited that mass years of nuclear research. Modern physics, the study of the properties, changes, and inter- has energy—expressed as the equation "E=mc2."7 This equation became one of the hall- actions of matter and energy, is basically the study of the atom and its components. It marks of modern physics. It stressed the interchangeability of matter and energy, and sug- began with the discovery of radiation in 1895, even though it was not then known that gested the huge amount of energy that could come from a small amount of matter.8 It also radiation came from the atomic decomposition of radioactive elements. Slowly at first, paved the way for an understanding of gamma rays, the third and most penetrating type of and then with increasing speed, physicists unlocked the secrets of atomic structure, the radiation emitted by radioactive elements. Albert Einstein, 1922. Burndy awesome power of fission, and finally, thermonuclear reactions. From the smallest com- By the time Einstein published his theory of relativity, the notion of atoms as the Library, courtesy of AIP Emilio Segré Visual Archives. ponents of the natural world came what could be its biggest threat and perhaps its greatest building blocks of all elements was coming into acceptance. Before then, the idea of the opportunity. This chapter will show how these momentous events occurred, beginning atom, which went back to the ancient Greeks, was useful only as a concept. Prior to the with the discovery of x-rays at the end of the nineteenth century. 1900s, no one actually knew anything about atoms, or if they even existed. Although John Dalton had hypothesized their existence in the early 1800s, at the end of that century, even as respected a physicist as Max Planck could publicly doubt the existence of atoms as EARLY DEVELOPMENT OF NUCLEAR PHYSICS actual particles.9 By the early 1900s, this was no longer the case. Not only were atoms thought to exist, but Rutherford’s increasingly sophisticated experiments also indicated Wilhelm Roentgen discovered x-rays in 1895 as a mysterious emanation from the flu- that the area of each atom was not solid, but mostly empty space. In 1911, Rutherford orescing glass wall of a cathode ray tube.1 Even though the source and the nature of the showed by bouncing alpha particles off atoms at large angles, that the bulk of an atom was new rays were unknown, they found almost immediate medical application as a means of contained in a central nucleus that had a positive charge.10 This experimentation identified seeing into the human body.2 The discovery of x-rays led to the testing of various natural- the basic electrical structure of the atom, with negatively charged electrons orbiting a posi- ly fluorescing materials to see which, if any, produced the mysterious rays. Henri tively charged nucleus. Becquerel soon discovered that uranium salts also produced these rays, and Marie and This scheme, which can be visualized as a small solar system with the nucleus at the Pierre Curie continued his work. Marie Curie named the mysterious force "radioactivity."3 center surrounded by orbiting electrons, was only a useful way to describe what was really The Curies devoted their lives to the study of radioactive elements, or unstable elements unknown in 1911. The bond that tied an electron to the nucleus was recognized to be that emitted radiation. In addition to the previously known uranium and thorium, the much greater than a gravitation field. The nature of the force that bonded the components Curies discovered radium and polonium. By the early 1900s, their studies led to the iden- of an atom remained a mystery until Danish physicist Niels Bohr wrote On the tification of some 30 radioactive isotopes.4 Constitution of Atoms and Molecules in 1913. According to Bohr, the forces that made for Marie Curie, 1906. Courtesy of AIP While the Curies studied radioactivity, English physicist J. J. Thompson discovered a stable atom could not be explained by the laws of classical physics, but only by the Emilio Segré Visual Archives. the first component of the atom, the electron, in 1897. This new particle was identified in quantum principles pioneered by Planck and Einstein.11 Ernest Rutherford, circa 1920. the course of Thompson’s work with cathode rays, which Thompson showed were actually In 1919, after the First World War, Rutherford, working at the Cavendish Laboratory Nature, courtesy of AIP Emilio Segré Visual Archives. small negatively charged particles he called "corpuscles." The new particles were lighter at Cambridge, became the first person to artificially transmute an element. Using alpha than atoms of hydrogen, the lightest of the elements. For this reason, Thompson guessed particles, he bombarded atoms of nitrogen to create hydrogen atoms.12 As a result of this that they must be a part of an atom that was somehow ejected from the whole.5 work, he also discovered, within the nucleus, a high-energy positively charged particle he called a "proton."13 This discovery completed the electrical make-up of the atom, with a An Atomic History 0-3 8/11/02 7:30 AM Page 6

Chapter One 9 positively charged nucleus (protons) surrounded by negatively charged electrons. The year but without an electrical charge, was discovered when Chadwick bombarded various light 1919 was also important because it provided scientists the opportunity to prove Einstein’s elements with alpha particles from a poloniumÐberyllium source. When the beryllium theory of relativity when light was observed to bend during a solar eclipse. source consistently knocked protons out of a whole range of light elements, he knew it was the work of something more powerful than gamma radiation. As a result of this work, Chadwick was able to show that the force that kicked out the protons was a new particle DEVELOPMENTS IN THE 1920s with a mass similar to that of a proton. Since it had no charge, the new particle was called a "neutron."20 In the decade after World War I, physics took its place at the cutting edge of modern The discovery of the neutron marked the true beginning of modern physics. Not only science throughout Europe and the United States. Berlin in particular came into its own did it provide the missing link to man’s knowledge of the atom, but it also provided a more during this period. The physics faculty of the University of Berlin included Albert practical means of transmuting an atom. Electrically neutral, neutrons could be used as a Einstein, Max Planck, and Max von Laue, the 1914 Nobel laureate in physics. In addition, more efficient probe to further explore the nucleus of the atom. The discovery of the neu- there were the various Kaiser Wilhelm Institutes for chemistry and physical chemistry in tron put physics on the road to the atomic bomb and the development of atomic energy.21 the Berlin suburb of Dahlem. Among the researchers there was the team of Otto Hahn and Lise Meitner.14 The great achievements of this period were theoretical breakthroughs. In 1922, Niels Bohr explained basic atomic structure, with atoms having various orbital FIRST TRANSMUTATION OF NUCLEUS AND ITS IMPLICATIONS "shells" of electrons, each shell capable of holding only a certain number of electrons. Bohr linked chemistry to physics when he discovered that atoms of a particular element The discovery of the neutron in 1932 was followed almost immediately by additional display a unique chemical behavior because of the number of electrons in their outer work on the transmutation of natural elements. Ironically, neutrons had nothing to do with shells. Molecular bonds could now be explained as a tendency to fill or empty the outer these early achievements. In 1932, researchers at the Cavendish Laboratory turned lithium shell by trading or sharing electrons.15 into helium, each lithium nucleus split into two helium nuclei, after bombarding the lithi- In the mid-1920s, Bohr, Werner Heisenberg, and Erwin Schrodinger advanced quan- um with protons made in a particle accelerator.22 In France, Joliot-Curies offered the first 23 Lise Meitner and Otto Hahn, 1913. tum theory with their exploration of the waveÐparticle duality of both matter and light. chemical proof of artificial transmutation, and his work was done with alpha particles. Leo Szilard, circa 1930. Bulletin of the Courtesy of AIP Emilio Segré Visual Heisenberg’s theory led to the "uncertainty principle," the concept that complementary Despite these successes, it appeared that this remarkable knowledge would never have Atomic Scientists, courtesy of AIP Archives. Emilio Segré Visual Archives. variables such as location and momentum could not both be measured precisely at the more than a limited application. Splitting atoms with proton beams and alpha particles same time. Schrodinger’s wave treatment yielded similar results when it was determined required powerful accelerators and a huge amount of energy. Both protons and alpha par- that many variables could be evaluated only in terms of statistical probabilities.16 ticles are positively charged, and they have to be driven against a positively charged nucle- American physics was less theoretical, but more practical, and it too came into its own us, since the natural tendency of both is to avoid each other. The collision success rate is during this period. By the late 1920s, John Douglas Cockcroft and E. T. S. Walton in at best about one in a million.24 Even though physicists knew of the awesome energy that Britain were developing a voltage multiplier, Robert Van de Graaf was working on his could be released by splitting the atom, they also knew that to do it with proton beams and electrostatic generator, and Ernest Lawrence at the Berkeley Radiation Laboratory was alpha particles was to use more energy than could be generated. A chain reaction would perfecting his atomic particle accelerator, the cyclotron.17 Although Cockcroft and Walton be virtually impossible. It was for this reason that Ernest Rutherford, in 1933, called the are credited with making the first transmutation using artificially accelerated protons, Van idea of atomic power "moonshine."25 de Graaf’s generator and Lawrence’s cyclotron became the more useful machines. Leo Szilard, in 1933, was one of the first persons to envision a nuclear chain reaction, Conceived by Leo Szilard in Germany as early as 1928, the cyclotron was a device for and one of the first to consider using neutrons as the bombarding agent. Because neutrons accelerating nuclear particles in a circular magnetic field.18 It was designed to bombard had no electrical charge, they could slip past other electrically charged atomic particles, the nuclei of different atoms, using accelerated protons speeding at million-volt energies.19 and thus would not have to be driven into the nucleus at high speed.26 For Szilard, howev- The tremendous speed was needed to overcome the electrical repulsion of the positively er, the idea remained a quixotic notion. An unemployed refugee from Hitler’s Germany, charged protons fired against the positively charged nuclei. At the time of the first then living in England, Szilard had neither the means nor the laboratory techniques to fur- cyclotron, the neutron, the neutral portion of the nucleus, had not yet been discovered. ther this idea. The man for this job was Enrico Fermi.

DISCOVERY OF THE NEUTRON: NUCLEAR PHYSICS COMES OF AGE FERMI’S WORK WITH NEUTRONS, 1930s

The discovery of the neutron by James Chadwick, in 1932, completed the identifica- In the 1930s, Fermi worked at the edge of the physics world in Mussolini’s Italy. tion of the major components of the atom. The neutron, with the same mass as a proton After the discovery of the neutron, Fermi decided to concentrate on experiments in artifi- An Atomic History 0-3 8/11/02 7:30 AM Page 8

DISCOVERY OF THE NEUTRON: NUCLEAR PHYSICS COMES OF AGE FERMI’S WORK WITH NEUTRONS, 1930s

Chapter One 11 cial radioactivity. His goal was to induce radioactivity or to transmute an element into inversely with the velocity. Fermi also discovered a suitable medium for slowing down another similar to itself; the idea of actually splitting a nucleus with neutrons was not part the neutrons: paraffin—or more specifically, hydrogen atoms.28 Later, carbon was found of the plan. Using radon and powdered beryllium as a neutron source, Fermi began bom- to be a good "moderator."29 barding the whole range of elements, beginning with the lightest in the periodic table. The Unusual things happened when Fermi got to uranium, the heaviest of the natural ele- first element to be made radioactive through this process was fluorine, followed by alu- ments. Neutron bombardment led to the creation of a heavier isotope, uranium-239, which minum. As a result of this work, Fermi found that light elements usually mutated into then decayed to a new man-made element with an atomic number of 93. Other substances even lighter elements by losing a proton or an alpha particle. Heavier elements tended not were created that could not be identified since they were not similar to uranium. The pos- to split, but became heavier.27 Fermi also discovered that the speed of the invading neu- sibility that uranium nuclei had split, creating totally different elements much further down trons was not an advantage, as it was with protons and alpha particles. With a few excep- the periodic table, was not considered at the time.30 Fermi continued this line of work tions, neutrons were absorbed more strongly at low energies, the absorption varying until 1938, when Mussolini issued his first anti-Semitic laws, threatening the safety of Fermi’s wife. When he was awarded the Nobel Prize that same year, Fermi and his family took the occasion to escape to London before moving on to the United States.31 By then, Components of the Atom others had joined in the exploration of the unusual nuclear properties of uranium.

By the mid-1930s, the basic concept of the atom number of protons. They do, however, have different had been established. The core is a positively nuclear properties, and these are identified by their NATURE OF URANIUM charged nucleus, comprised of neutrons and posi- atomic mass number, or number of protons and neu- tively charged protons, orbited by negatively charged trons. In this fashion, natural uranium basically con- Long thought to be an extremely rare substance, uranium ore, originally known as electrons. As a rule, protons and electrons are equal in sists of two isotopic forms; it is 99.28 percent uranium-238 pitchblende, was first used to color ceramics in Renaissance Europe. At that time, and for number, balancing each other out. (Physicists have discov- and 0.712 percent uranium-235. centuries to come, the only known source was from the Joachimsthal mines in what is now ered a number of subatomic particles, but the behavior and make-up Isotopes with too many, or few, neutrons for their own stability 32 of ordinary matter is determined by neutrons, protons, and electrons.) emit radioactive particles to correct the imbalance, a process known as the Czech Republic. The heaviest natural element on earth, uranium is radioactive, but In the mid-1930s, Bohr arrived at the basic configuration of the nucle- radioactive decay. Although other types are known, three basic kinds not strongly so, and can be handled without special protection. Like most natural radioac- us, which does not form a solid mass, but is comprised of protons and of radiation are emitted during this decay: alpha particles, beta parti- tive elements and isotopes, uranium is radioactive because it is in the slow process of neutrons closely packed together in such a way that they could be split cles, and gamma radiation, all of which were identified by the mid- decaying—in the case of uranium, to a stable isotope of lead. The only reason it even apart. This theoretical framework is supple enough to allow for the 1930s. Alpha particles are formed by two protons and two neutrons, exists naturally is that it has an extremely long half-life: 4500 million years for uranium- existence of isotopes, which are unstable radioactive variants of more and have a positive charge. Very weak, alpha particles can be stopped 238; 700 million years for the much rarer uranium-235.33 stable elements. by skin or a sheet of paper. The more powerful beta particles are All forms of uranium have 92 orbital electrons and 92 protons in the nucleus, which By this time, the main parts of the atom were also classified in a formed when a nucleus contains too many neutrons for stability. At gives them an atomic number of 92. There are 14 known isotopes of uranium, each with a modern fashion. Protons and neutrons, which together compose the that point, a neutron changes to a proton and ejects one of the orbit- different number of neutrons in the nucleus. Identified by their mass number (protons plus nucleus of the atom, each have an atomic mass of 1; electrons have a ing electrons. Beta particles can also be formed when there are too neutrons), these isotopes range from uranium-227 to 240. By far the most important of much smaller mass, 1/1840 of either a proton or a neutron. The num- many protons for stability, and a proton changes to a neutron by eject- 34 these are uranium-238 (with 146 neutrons) and uranium-235 (with 143 neutrons). The Enrico Fermi, circa 1930. NARA, ber of protons, also identified as the atomic number, determines the ing its positive charge in the form of a positron, a particle discovered uranium atom requires a high number of neutrons because its nucleus is so crowded with courtesy of AIP Emilio Segré Visual element of the atom. For example, carbon has an atomic number of 6 by Carl Anderson at California Institute of Technology in 1932. Gamma Archives. positively charged protons that they tend to repel each other. These properties make the because there are 6 protons in each carbon nucleus. In similar fash- rays have neither charge nor mass. Gamma rays typically appear as ion, uranium has an atomic number of 92 since each of its atoms con- a result of alpha or beta emission. Positive beta particles, or positrons, nucleus unstable and relatively easy to split. tains 92 protons. Mass number represents the total number of pro- provide an additional source of gamma rays. When positrons combine This instability is more pronounced in the man-made "transuranium" elements, which tons and neutrons in the nucleus. The most stable of the lighter ele- with electrons, they annihilate each other and create gamma rays. This are packed with even more protons than natural uranium. In the 1930s, these artificial elements have an even number of protons and neutrons. The heavier ele- is the only common reaction in which isolated masses are totally con- ments were theoretical, but tentatively identified. Element 93 (later known as neptunium) ments have more neutrons than protons, an arrangement that helps to verted to pure energy. and Element 94 (later known as plutonium), were originally known as Eka-rhenium and hold the heavier nuclei together. For elements heavier than lead, the Eka-osmium, respectively, based on their theoretical position in the periodic table. nucleus is so unstable as to generate radioactivity. Such elements are Source: E. H. Lockwood, Reactor Physics Primer (Richland, more susceptible to the formation of isotopes. Washington: Operational Physics, Research, and Engineering Isotopes of a given element are composed of atoms with the Operation, GE, Hanford Atomic Products Operation, 1957), 2-8. Henry DISCOVERY OF FISSION, 1938/1939 same atomic number as the most common form of that element, but DeWolf Smyth, Atomic Energy for Military Purposes: The Official with different mass numbers. In other words, their nuclei contain a dif- Report on the Development of the Atomic Bomb Under the Auspices During the 1930s, when nuclear physics was assuming its modern form, the physics ferent number of neutrons. Chemically, isotopes are indistinguishable of the United States Government, 1940-1945 (Princeton; New Jersey: world itself was convulsed by the rise of Hitler and his anti-Semitic agenda. Appointed from other variants of a given element, since both contain the same Princeton University Press, 1945), 12. German chancellor on January 30, 1933, Hitler assumed dictatorial powers in the wake of An Atomic History 0-3 8/11/02 7:30 AM Page 10

Chapter One 13 the Reichstag fire a month later. By March, Jewish judges and lawyers were dismissed Bohr’s news of the fission process swept through the American physics world later in from their positions in both Prussia and Bavaria, with the other German states soon fol- January of 1939.42 The theoretical possibility of a nuclear chain reaction was almost lowing. In April, the Nazis began a national boycott of Jewish businesses, and Jews began instantly perceived. Fermi, now at Columbia University, certainly considered this a possi- to lose their university positions.35 bility.43 It was an avenue further explored throughout the rest of 1939, as Europe slid into These developments, and the worse ones to follow, war, and as the awesome possibilities of uranium fission increasingly pointed to the possi- devastated the world of German physics. Before the end bilities of an atom bomb. of 1933, Albert Einstein, Leo Szilard, Eugene Wigner, and Edward Teller had left Germany for positions in England and, eventually, the United States. Others soon followed. FISSION DEVELOPMENT, 1939 In all, over 100 physicists left Germany during the 1930s.36 While this exodus was a disaster to German Almost overnight, fission became an obsession within the nuclear physics physics, it was a boon to the United States. In the 1930s, community.44 While work also continued on the development of transuranic elements, the physics world shifted its center of gravity from Britain especially Element 93, the year 1939 was largely dedicated to unlocking the secrets of the and Germany, to a new trans-Atlantic nexus. uranium atom, and determining the methods by which it could be split. Despite the devastation to German physics, there In early 1939, while Bohr was still in the United States, he realized the significance of were still enough scientists in the Third Reich to make uranium-235 to the fission process. Knowing that both thorium and uranium captured new discoveries. Among those who stayed, or were slow neutrons, while only uranium fissioned, Bohr reasoned that the difference between allowed to stay, were Werner Heisenberg, Fritz the two had to be the presence of uranium-235, which is less than one percent of natural Strassmann, and the team of Otto Hahn and Lise Meitner. uranium. Bohr’s insight was that only uranium-235 fissioned.45 This insight commenced Although Meitner was Jewish, she was allowed to remain experimental work to isolate enough uranium-235 to test Bohr’s theory. at the Kaiser Wilhelm Institute because she was an The possibility of a chain reaction, first conceived by Leo Szilard, quickly took on Austrian national.37 Taking a cue from Fermi’s work in heightened significance as fission research continued. A fission chain reaction required Italy, Hahn and Meitner concentrated their efforts on fur- that a neutron enter and split a uranium nucleus, which would then send off other neutrons ther unlocking the secrets of uranium. By 1938, they had that would enter yet more nuclei, and so on. It was quickly realized that, under most cir- made 10 different isotopes of the element, and were cumstances, a chain reaction could not occur in natural uranium; uranium-235, however, already exploring the transuranics. That year, their offered possibilities. A controlled chain reaction, which might be used to harness electric- research was interrupted by Hitler’s seizure of Austria, ity, could be achieved with natural uranium enriched with a higher percentage of uranium- which forced Meitner to flee to avoid the impact of 235. An uncontrolled reaction, or a bomb, might be achieved with a much higher concen- Hitler’s anti-Jewish laws.38 Hahn and Strassmann contin- tration of uranium-235.46 Beginning in early 1939, Szilard, Fermi, Walter Zinn, and oth- ued the uranium work. ers studied the possibilities of a nuclear chain reaction.47 In December of 1938, Hahn and Strassmann made the An important component of this chain reaction work was the study of suitable "mod- momentous discovery that uranium atoms (atomic number erators," the material placed around the uranium to slow down the neutrons and increase 92), when bombarded with neutrons from a radiumÐberyl- the chances of nuclear fission. The first agent to serve as a moderator was water, which lium source, would actually split into two radioactive contains the hydrogen needed to slow down the neutrons. Water, however, had a high par- atoms of roughly equivalent mass, the heaviest of which asitic absorption rate, and would not work for natural uranium, even though it could be was barium (atomic number 56).39 This had been done made to work if the percentage of uranium-235 were increased. This left beryllium, earlier by Fermi and others, but none had recognized the graphite, and deuterium oxide, also called "heavy water." Beryllium was both too expen- Niels Bohr with the Cockcroft-Walton result. Hahn quickly relayed this breakthrough to Meitner, then working in Sweden with sive and too hazardous. Graphite and heavy water were much more promising, but the use accelerator, 1930. Niels Bohr Archive, her nephew, Otto Frisch. of either would not be easy.48 In the case of graphite, the problem was quality; in the case courtesy of AIP Emilio Segré Visual Archives. Meitner and Frisch did further calculations on the results in December and into of heavy water, quantity. It was difficult to make graphite of sufficient purity to serve as a January of 1939, and were able to show theoretically that the splitting of uranium atoms moderator. In the case of heavy water, there simply was not enough. The only industrial (Overleaf) Graphic illustration of the released a large amount of energy. The secret to the process was Einstein’s old formula, facility that produced heavy water was a plant in Norway, and it produced relatively small difference between fission and fusion 2 40 used in 1950s era booklet on atomic E=mc , with energy created by reducing a part of the mass of the nucleus. Frisch and amounts for electroplating. It would not be easy to produce more. Deuterium could not be energy. Source: M. Phillip Copp, Meitner even named the new process, "fission," from a biology term for the binary separa- made chemically, but had to be "harvested" from natural water, where it is found in minute Booklet entitled The Atomic tion of a cell.41 Later that same month, they told Niels Bohr of their calculations, just quantities: one deuterium atom for every 7000 regular hydrogen atoms.49 Even the place- Revolution, 1957. Courtesy of SRS History Project. before Bohr left Copenhagen for a trip to the United States. ment of the moderator had to be worked out to achieve optimum effect. The use of heavy An Atomic History 0-3 8/11/02 7:30 AM Page 12

Chapter One 15 An Atomic History 0-3 8/11/02 7:31 AM Page 14

Chapter One 15 An Atomic History 0-3 8/11/02 7:31 AM Page 16

Chapter One 17 water required tanks and plumbing systems, while graphite blocks would have to be ties for harvesting uranium-235, but no one knew if any of them would work, and all of arranged both around and in between the uranium. In 1939, Szilard came up with the idea them promised to be prohibitively expensive. In effect, this was the state of fission of a lattice arrangement for the graphite blocks as a moderator.50 research when Hitler invaded Poland and began World War II in Europe. Germany, At the end of 1939, most of these issues and their solutions were still theoretical. No Britain, and the United States, all had the knowledge and the means for making an atomic one had gathered enough graphite or heavy water to test these materials as actual modera- bomb. All they lacked was the will. tors in a chain reaction. More importantly, no one knew how to gather enough uranium- On the eve of the First World War, H. G. Wells published The World Set Free, a novel 235 to create a chain reaction, much less make a bomb. There were a number of possibili- that described a world run by "atomic energy," and a global war in which cities were destroyed by "atomic bombs." Physicists from Heisenberg to Szilard had long been intrigued by Wells’ story.51 What had been an outlandish fantasy during the First World War would be within the realm of possibility during the Second. Most physicists knew THE WORLD SET FREE this, and, at varying levels of involvement, so did their governments. In late 1939, "The problem which was already being mooted by Heisenberg, Hahn, and others were commissioned by the German military to continue by H.G. Wells, 1914 such scientific men as Ramsay, Rutherford, and Soddy, in research into the possibility of a nuclear chain reaction and the possibility of a bomb.52 the very beginning of the twentieth century, the problem of Similar research began in both Britain and the United States, even though the U.S. inducing radio-activity in the heavier elements and so tap- government was not yet involved. Leo Szilard moved to correct this situation by enlisting ping the internal energy of atoms, was solved by a won- Einstein to write a letter to President Roosevelt in August of 1939, warning him of the derful combination of induction, intuition and luck by Holsten so soon as the year 1933. From the first detection possibility of a new and potentially awesome type of bomb, a bomb the Germans were of radio-activity to its first subjugation to human purpose probably working on. As a result of this letter, in October, Roosevelt commissioned the measured little more than a quarter of a century. For twen- first U.S. government agency to look into the potential of this line of research: the 53 ty years after that, indeed, minor difficulties prevented any Advisory Committee on Uranium. This was the first in a long series of steps toward the striking practical application of his success, but the essen- Manhattan Project. tial thing was done, this new boundary in the march of human progress was crossed, in that year. He set up atomic disintegration in a minute particle of bismuth, it exploded with great violence into a heavy gas of extreme radio-activity, which disintegrated in its turn in the course of seven days, and it was only after another year’s work that he was able to show practically that the last result of this rapid release of energy was gold. But the thing was done, --- at the cost of a blistered chest and an injured finger, and from the moment when the invisible speck of bismuth flashed into riving and rending energy, Holsten knew he had opened a way for mankind, however narrow and dark it might still be, to worlds of limitless power.

Source: Wells, H. G., The World Set Free. E. P. Dutton & Company, New York, 1914: 40-41. Image from M. Phillip Copp, Booklet entitled The Atomic Revolution, 1957. Courtesy of SRS History Project. An Atomic History 0-3 8/11/02 7:31 AM Page 16

Source: Wells, H. G., The World Set Free. E. P. Dutton & Company, New York, 1914: 40-41. Image from M. Phillip Copp, Booklet entitled The Atomic Revolution, 1957. Courtesy of SRS History Project.