| History 4000 The Development And Use Of The Atomic Bomb Lesson One: The Science Behind The Bomb
Three forms of knowledge were needed to produce atomic weapons. They were: 1) the structure of the atom, 2) the nature of radioactive energy, and 3) the ability to harness radioactive energy to produce a controlled chain reaction.
J. J. Thomson 1884 became Director of the Cavendish Laboratory, Cambridge University. Made Cavendish Laboratory the premier center for study of nuclear physics. Demonstrated that the electron (Cathode ray) was negatively charged and was therefore the first to prove the existence of subatomic particles. Developed the "plum pudding" model of the atom, wherein an equal number of negative and positive charges were mixed together. Subsequently, he and his student, Ernest Rutherford, demonstrated that X Rays produce ionization of the air, give air an electrical charge. Received the Nobel Prize for physics in 1906.
Wilhelm Roentgen On November 8, 1895, Roentgen was working in his laboratory at the University of Wurzburg in Germany. He was studying the properties of electrons and had a cathode ray tube in his laboratory. He noticed that a fluorescent screen was glowing on a nearby table and deduced that it was caused by light rays or energy emanating from the cathode tube. But he wrapped the tube in black paper and discovered that the screen still glowed. He then had his wife place her hand on a photographic plate, developed the picture, and discovered that the ray or energy penetrated his wife's flesh, but not her bones. Because he did not know the nature of these rays, Roentgen called them X Rays. He received the Nobel Prize in Physics, the first, in 1901. Henri Becquerel A French physicists, Becquerel was interested in the phenomenon of phosphorescence --the spontaneous emission of light by a substance after the source of stimulus has been removed. In 1896 he was particularly focused upon investigating whether there was any connection between phosphorescence and X Rays. He had inherited from his father a supply of uranium salts, which phosphoresce when exposed to light. One day in 1896 when there was no sunlight, he placed the uranium salts and a photographic plate in a drawer. To his dismay Becquerel observed several days later that when he removed the material from the drawer, the image of the uranium salts on the plate was clearer than even when exposed to sunlight. This was a momentous discovery -- the discovery of spontaneous radiation. Marie and Pierre Curie Marie Curie (she first used the term "radiation"), a Pole, and her French husband were intrigued by Becquerel's discovery of the spontaneous radioactivity of uranium. They laboriously worked with tons of an ore called pitchblende which contained uranium and found that the spontaneous energy it produced was greater than pure uranium. They thereby deduced that pitchblende must contain other radioactive elements, which they identified as polonium (named for Poland) and radium. They announced their discoveries in 1900. Their most important contribution was to demonstrate that the quality of radioactivity resulted from the internal composition of the atom itself. Becquerel and the Curies jointly received the Nobel Prize in Physics for 1903. The great majority of
elements are stable and do not spontaneously emit energy. There are,
however, some elements, such as uranium, that are in a process of decay.
The emission of energy is direct result of that decay.
To become stable,
unstable atoms emit radiation in the form of particles, such as alpha and
beta radiation, or in the form of electromagnetic waves, such as gamma
radiation and X-rays.
Albert Einstein. In 1905, Albert Einstein published a paper in which he set forth the Special Theory Of Relativity. In terms of the eventual development of atomic weapons, Einstein's major contribution was to theorize that energy and matter are manifestations of the same physical entity and that the relationship between energy and matter can be expressed in the formula E=MC2. Any loss in mass will result in an increase of energy.
Ernest Rutherford A New Zealander and student of J. J. Thomson's, Rutherford conducted experiments to test alternative models of the internal structure of the atom. His accomplishments were many and prodigious. He was the first to demonstrate that radioactive materials emit energy spontaneously because they are going through a process of decay and that during this process they experience transmutation -- they turn into a different substance. Such a notion would have been considered nonsense theretofore. But his most important discovery occurred in 1909. He was bombarding a piece of thin gold foil with Alpha particles. Alpha particles are relatively large, positively charged particles emitted by uranium and other radioactive materials. Can be stopped by paper or skin, but extremely damaging if swallowed or inhaled. The vast majority of the Alpha particles passed though the foil but a small number bounced back. He concluded that the mass of the atom was concentrated in a positively charged nucleus and that the electrons occupied the outer reaches of the atom. This led him to develop a planetary model of the atom and the discovery of the proton.
Neils Bohr A Dane and another student of J. J. Thomson's, Bohr made a major refinement to Rutherford's planetary model of the atom in 1913. According to standard electromagnetic theory, the electrons would emit electromagnetic energy because of their orbital motion, would thereby lose speed, would eventually spiral downward into the nucleus of the atom, and the atom would implode. Obviously this did not happen. Bohr posited that electrons exist within shells of energy or discrete orbits and therefore remain stable. The only time they move, from a higher to a lower shell of energy or the reverse, is when the atom receives or emits radiation. If it emits radiation, the electrons move to a lower shell. If it receives radiation, the electrons move to a higher shell. Also, Bohr posited that the nucleus of the atoms are shaped like a tear drop -- an important concept in eventually explaining the process of nuclear fission. James Chadwick In 1907 Chadwick mistakenly stood in the line to register as a physics major at the University of Manchester. He had intended to be a mathematician, but he was too shy to admit that he had made a mistake. He knew that Rutherford had speculated about the existence of a neutrally-charged subatomic particle. In 1930 Chadwick demonstrated the existence of the neutron. This opened the door for chain reactions. Chadwick received the Noble Prize in Physics in 1935.
Frederic Joliot and Irene Joliot Curie Irene Curie, daughter of Marie Curie, was a physicist, and her husband was a chemist. Their most important discovery was the possibility of manufacturing "radioactive material," and not having to depend totally upon natural elements. In 1934 they bombarded aluminum and boron with alpha particles and were astonished to observe that positrons, positively charged subatomic particles, were still emitted after the bombardment was stopped. This meant that they had produced an artificial radioisotope of nitrogen. A single element contains nuclei of different numbers of neutrons. These are called "isotopes." This discovery was to have enormous implications for medicine. This suggested that fission of heavier elements into lighter ones and the fusion of lighter elements into heavier ones by bombardment of atoms was within the grasp of human capacity. Otto Hahn Otto Hahn, a German chemist, heard the news of the Joliot-Curie experiment and set out to prove that their results were bogus. Working with associate Otto Strassmann, he reproduced in December 1938 the experiments and found that it was true that some atoms of the element uranium produced atoms of the lighter element barium. Being a chemist and aware that this defied all the known laws of physics, Hahn turned to his former co-worker Lise Meitner for an explanation. Lise Meitner A German physicist and a Jew, Lise Meitner worked for many years in collaboration with fellow physicist Otto Hahn. In 1938, she was forced to leave Germany because of the Nazi regime. Otto Hahn wrote to her in Sweden, stating that he had demonstrated by bombarding uranium with neutrons that the uranium was transmuted into barium, a much lighter element. How was this possible? Living in Sweden, Meitner hypothesized that in some instances the nucleus of the uranium atom, shaped like a tear drop, oscillated under bombardment into a dumbbell-like shape and that the thin neck broke off due to the repulsive force of the protons in each bulb, thereby producing nuclear fission or the splitting of the atom. One of the results of the lessening of mass was the release of energy and the ejection of neutrons. An article, co-written with her nephew Otto Frisch, explaining the process, appeared in the journal Nature in January 1939. This alarmed those physicists, such as Leo Szilard, who understood the destructive force that could be produced by a chain reaction.
Enrico Fermi An Italian physicist and the husband of a Jew, Fermi came to the United States in 1938 to join the Physics Department of Columbia University in New York City. Before leaving Europe he had learned of the Joliot-Curie experiments and had come to recognize the possibility of using heavy, radioactive elements, such as uranium, to produce neutron bombardments that would lead to a chain reaction if the recipient material was sufficiently unstable-- a process that would produce enormous amounts of energy. Leo Szilard A Hungarian Jew, German-trained physicist and Fermi associate Leo Szilard recognized the potential of using nuclear energy to fuel a terrible bomb. Terrified that Germany might develop such a weapon, Szilard, who had moved to the United States, visited with Dr. Albert Einstein in the Summer of 1939 and urged him to write a letter to President Franklin Roosevelt urging the United States to move forward with atomic bomb development. Click Here To Read Einstein's Famous Letter.
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