Atomic bomb Example For Students

Atomic bomb Where did the atomic bomb come from? In this paper, I will look at the development of the ideas needed to create an atomic bomb. Specifically, what did scientists need to know for them to theorize that a cataclysmic explosion would result when a critical mass of certain elements undergo a chain reaction of nuclear fission. However, I will only look at scientific ideas generally, as they progressed towards fission. This development of ideas was propelled by genius, persistence and tenacity, coupled with flashes of insight into the nature of the universe. We see that this development is tied closely to the ability to free the teathers of erroneous paradigms and build better models of the universe in their place. We will be concerned, principally, with the development of physics. Einstein wrote the following on the definition of physics: What we call physics comprises that group of natural sciences which base their concepts on measurements; and whose concepts and propositions lend themselves to mathematical formulation. (Weaver, 78) Although physics today is more focused, this is the basis of all science. One of the first groups of people to freely think about the universe and make an attempt to explain their world scientifically were the Greeks. II. The Greek Ideology The Greeks investigation of science demonstrate that their minds were on par with the best of this era, specifically Aristotle (384 322 B. C. ), who formed many brilliant theories. He, along with others, put the theories into sophisticated form that created the basis of scientific thought for close to two millennia. In his universe were four elements: Earth, Water, Air, and Fire. The Earth was the common center of all the solid materials and had a natural place as the center of the universe. If all the solid material sought a location as close to the center as possible, then the Earth had to be a sphere. He had likewise ordered the other elements into spheres. Water had its natural place on the surface of the sphere Earth. Air had its natural place on the surface of the sphere Water. Fire had its natural place outside the sphere of Air. Observations corresponded to this view of the universe. However, he performed no experiments. He stated that heavier objects would want to move faster toward their respective spheres than lighter objects. It is regrettable that he did not perform any of a number of simple experiments to prove or disprove his ideas. These Greek philosophers worked to explain the motion of matter. Their ordering of the universe defined what happened when an element found itself outside of its sphere. It simply sought its correct sphere. They also did well with basic types of motion, stating that when one object had contact with another it would create motion in that object. There were other types of motion they had trouble with. For instance, why does a ball keep rolling even after your hand no longer has contact with it? Another problem that arises from the Aristotelian classification is how would two objects affect each other in a vacuum? Aristotle had theorized that vacuums would create difficulties, but in his day they were only considered a philosophical abstraction. The problem did not need to be dealt with seriously. Nevertheless, motion in the absence of the element Air was unthinkable. For them, Air had inherent physical properties. Also, it encompassed everything that could possibly have motion. The absence of Air meant the absence of motion. Before we can answer these questions, however, we must look at when and how observation combined with experimentation. III. Unifying Observation and Thought with Experimentation The Aristotelian universe was generally accepted for about 1600 years. During the late Middle Ages the view began to change slowly. Scholars began to view experimenting as a method of testing theories. The following passage explains the beginning of the change in ideas when scientists used experimentation methodically. Historically we may say the revolution in ideas began with Copernicus and his heliocentric theory of the solar system, but Keplers work is much closer to modern science than that of Copernicus, for in formulating his three laws of planetary motion, Kepler proceeded much the way the contemporary physicist does in constructing theoretical models of structures such as atoms, stars, or galaxies. Even so, Galileo and Newton were the initiators of modern science, for whereas Keplers work was primarily empirical, the work of Galileo and Newton has all the elements of what we now call physics. This work was an enormous step forward in that it revealed the relationship between the motion of a body and the forces acting on it. (Weaver, 18) Lets back track slightly to Galileo Galilei (1564 1642). It was not until Galileo that the Aristotelian universe collapsed in a flurry of ingenious and conclusive experiments. Galileo did not invent experimentation, but he forever united it with science. For a brief background of Galileo, we turn to Segres From Falling Bodies to Radio Waves. Galileo passed the first ten years of his life in Pisa, went to Florence around 1574, and was back in Pisa in 1581, registering as a student of medicine at the university. When he was nineteen years old he became acquainted with geometry by reading books and meeting the mathematician Ostilio Ricci (1540 1603). what a revelation the discovery of geometry must have been for the young man. He was studying something probably distasteful to him, and all of a sudden he found the intellectual for which h e was born and which somehow had escaped him previously. Probably only passionate love can equal the strong emotion aroused by such an event. (Segre, From Falling , 16) Galileo was the first person to create a shop for the pursuit of scientific study. Some experiments dealt with time-keeping, not an easy task four hundred years ago. He dripped water down inclined planes and achieved useful results. He also experimented with rolling balls of various weights on these inclined planes. It is not difficult to prove that the amount of time for the ball to traverse the plane is independent of the mass of the ball. In other words, it requires an equal amount of time for two balls of different weights to roll down an inclined plane. From this, and other experiments, he made the generalization that all bodies fell through equal distances in equal times. There were other significant discoveries made. Aristotelian thought was proved incorrect. Or we may say the generalizations made by Galileo provides a base to explain more phenomena when compared to the Aristotelian universe. After other people performed experiments and formed theories, and a hundred years passed, Sir Issac Newton (1642 1727) enters the stage. Newton developed mathematical tools to help him solve the problems created by his scientific pursuits. The nature of the phenomena he was pursuing forced him to create calculus. The following passage fills in some of the details. Using the calculus, Newton deduced Keplers three laws of planetary motion. This changed the methodology of scientific research forever, for it showed that a correct physical law (Newtons law of gravity) combined with logic (mathematics) can reveal new truths with relatively little effort and in a relatively short time. Keplers empirical formulation of the laws of planetary motion represents some sixty man-years of research (thirty years of Tycho Brahes observation and thirty years of Keplers arithmetic analysis), were as Newtons derivation took only an hour or two. (Jefferson, 19) The development of the correct mathematical tools was an important event. When mathematics is combined with experimentation and thought, a new method of discovering the laws of nature is possible. The importance of this event can not be understated. Here is another example of the power of Newtons laws, applying thought and using mathematics. At the beginning of the 1800s , Uranus was found to have perturbations in its orbit. These perturbations were different from the orbit calculated by Newtons law of gravitation. This fact threatened to dismantle the Newtonian universe. Then in the 1840s, John Couch Adams (1819 1892) and Jean Joseph Leverrier (1811 1877), believing Newtons law to be correct, developed a theory which could account for the differences between the predicted location for Uranus and its actual location. This theory was that another planets gravitational influence was perturbing Uranuss orbit. Subsequently, Neptune was discovered. Still the difficulty of how objects affected each other remained. We return now to the different types of motion to appreciate the scientific problem facing people in the 17th century. IV. Action at a Distance Recall that the Greeks had difficulty explaining how a ball, once rolling, keeps rolling, and how objects would affect each other through a vacuum. Newton was able to explain the first problem with his first law: An object in motion tends to stay in motions. This is also know as inertia. The ball that is rolling stays in motion because the only way to change its motion is to subject it to more force. Community Service Projects, Lo EssayThese charges were concentrated in a comparatively small volume of space. This nucleus was circled by a similar number of negative charges. (He knew there were problems with this theory, but he used this theory in the same way that Newton was willing to use action-at-a-distance. It was close enough to make useful calculations. ) The alpha particles that shot into the foil and bounced back were deflected by the nucleus. This deflection was the result of the mutual repulsion two protons have for each other. It is governed by the mathematical description of Coulombs law. Without field theory, Rutherford would have had to figure out how two very small protons are able to feel each others presence inside an atom. But with field theory, he did not need to concern himself with it too much. Rutherfords next problem dealt with finding the neutron. The neutron had been hypothesized from the fact that helium has a weight of four protons but an electrical charge of only two. The question of the extra weight was perplexing. The idea of a neutral particle, with the properties that are associated with what is now known as the neutron, was first proposed by Rutherford in 1920. James Chadwick (1891 1974) and Rutherford performed a search for this theoretical particle, but were unable to prove its existence. Shortly, we will see what had to happen first to make the discovery of the neutron possible. Thus, the atom could be shown to exist. Shortly after Rutherfords evidence that the atom is like planetary system, but on a very small scale, was made known, many people commenced work in this new field which later became known as nuclear physics. Some, such as Rutherford and the Curies, made this topic their lifes work. The experiments lead to quantum mechanics, which was also worked on steadily through this time period. It is still pursued today, but unfortunately, we will not look at quantum mechanics in this paper. VIII. Fission Frederic Joliot (1900 1958) and Irene Curie (1897 1956), his wife, were performing experiments in 1931 with polonium, which had been discovered by her mother, Marie Curie. Their experiments produced very strange results; literal transmutations of elements were occurring at the atomic level for which they could not account. They published these results on January 18, 1932. When Chadwick saw the report he repeated the experiments, using additional elements, and proved that the radiation contained a neutral particle whose mass was approximate to that of a proton. He called it a neutron in a report sent to Nature on February 17, 1932. Continuing his work found that slow moving neutrons were more apt at producing these transmutations than protons. When he received the Nobel Prize in 1935, he discoursed on the usefulness of the neutron as a catalyst to fission. A small excerpt from his lecture follows. The great effectiveness of the neutron in producing nuclear transmutations is not difficult to explain. In the collisions of a charged particle with a nucleus, the chance of entry is limited by the Coulomb forces between the particle and the nucleus; these impose a minimum distance of approach which increases with the atomic number of the nucleus and soon becomes so large that the chance of the particle entering the nucleus is very small. In the case of collisions of a neutron with the nucleus there is no limitation of this kind. The force between a neutron and a nucleus is inappreciable except at very small distances, when it increases very rapidly and is attractive. Instead of the potential wall in the case of the charged particle, the neutron encounters a potential hole. Thus even neutrons of very small energy can penetrate into the nucleus. Indeed slow neutrons may be enormously more effective than fast neutrons, for they spend a longer time in the nucleus. (Weaver, 733) As stated in the quote, slow moving neutrons have a greater incidence of affecting the nuclei of the material than fast moving neutrons. By bombarding of the elements, and determining the reactions that took place, physicists found the neutron to proton ratio of a wide range of these elements. They also found that the neutron to proton ratio increased as the number of protons in the nucleus increased. The element with the most protons known at the time was uranium. It has 92 protons and 146 neutrons. (It is usually known as uranium-238. ) Bombarding uranium yielded the most spectacular results yet. The uranium atom was actually split into two atoms of approximately the same size and fission was accomplished. This released significant amounts of energy. It was found that an isotope of uranium, uranium-235, easily fissioned with slow neutrons to yield krypton and barium. Taylor, 353) Unfortunately, uranium-235 is found in naturally occurring uranium only about 1 part in 137. Extracting it is not an easy process. (Segre, From X-rays , 210) This provides the last piece of information needed to deduce the possibility of an atomic bomb. IX. Sustained Reactions The Atomic Bomb In 1940, Otto Frisch and Rudolph Peierls posed an important question. From Nuclear Fear, we may read this question. Exactly what would happen, they asked themselves, if you could cull from natural uranium a mass composed purely of the rare uranium-235? Bohr and others had told the public that there could be enough energy there to blow up a city, but nobody had worked it out as a serious technical possibility. Now Frisch and Peierls realized that with fissionable uranium-235 atoms all crammed together, there would be no need for a moderator to slow the neutrons down, since even the fast neutrons emitted in each fission would have a good chance to provoke another fission. The whole chain reaction would go so swiftly that, before the mass had a chance to blow itself apart, a run away many of the uranium-235 atoms split and release energy. (Weart, 84) This question may have been left academic for years had it not been for World War II. As the awesome power of an atomic bomb was realized by leaders of several countries, a race began to be the first to make a working bomb. As a result, a simpler method was discovered than separating uranium-235 from uranium-238. This simpler method starts when uranium-238 absorbs a single neutron a new element, called neptunium-239, is created. (Neptunium-239 has 93 protons and 146 neutrons. ) This element decays into plutonium-239 (94 protons and 145 neutrons). Plutonium is stable and also has the property of undergoing fission with slow neutrons. Hence, the atom bomb was conceivable. Plutonium was produced in a reactor. (Weart, 87) The United States was one of the nations was one of the countries searching for the technology to make the atomic bomb a reality. On July 16, 1945, they succeeded when the first atomic bomb was detonated. In an isolated spot named Alamogordo, moments before first light , night exploded noiselessly into day. Searing colors gold, purple, blue, violet, gray illuminated everything in sight. From the floor of the desert, a ball of fire rose like the sun (only brighter, one report read, equal to several suns in midday). Thirty seconds later came a blast of burning air, followed almost instantaneously by an awesome roar. A cloud the shape of an immense mushroom ascended nearly eight miles, was caught by the desert winds, and curled into a giant question mark. (Stoff, 1) This was the realization of a long trek through history. Thought and experiment combined with field theory, a knowledge of chemical properties of the elements, and the discovery of radioactivity. This gave people the ability to answer the question: What is the structure of the atom? Not only was the structure determined, but it was found that the number of protons and neutrons could change. Protons and neutrons together are known as nucleons particles that inhabit the nucleus. ) Changing the number of nucleons has several names: radioactivity, fission and fusion according to how the atom is changing and what is causing the change. Generally energy is released as a result of this change. Using Einsteins bold statement that E=mc^2, the nature of this energy became known. The energy is a direct conversion from part of the mass of the atom. As we saw, it was a short technological step to use the same source of energy for the sun, as a source of energy on the earth.