Ernest Rutherford and Nuclear Physics Contributions - Research Paper Example

?Born to simple and hardworking country folks in New Zealand, Ernest Rutherford was destined to become what some call, according to Dr. John Campbell, “the father of nuclear physics”. Though he showed no interest in science as a child beyond reading one science textbook, he forever changed the way that atoms and physics were thought of. Through his work and groundbreaking experiments, he was able to make many contributions to nuclear physics, from naming alpha and beta radiation (as well as the differences between the two), to splitting the nucleus of an atom in 1932. Ernest Rutherford was born on August 30, 1871, in Bridgewater, New Zealand, to James and Martha Rutherford. His father was a wheelwright, his mother a schoolteacher (Campbell). He moved once or twice, though staying in New Zealand the entire time, and attending different schools when he moved (Campbell). Though Ernest as a boy liked tinkering with clocks, and loved to make models of the wheels that were used in the mills, he did not show any real passion for science during childhood (Mahanti, 2011). Most of his education came through the winning of scholarships, first to Nelson College in 1889, then on to Canterbury College at the University of New Zealand, where he first developed an interest in electrical science, running experiments that would determine whether or not iron was magnetic at a high magnetizing frequency (Campbell). After failing in three attempts to secure a teaching position after university, and briefly considering medicine, he took odd jobs tutoring students to help make ends meet while continuing to experiment in electrical science. In 1895 he won a scholarship to Cambridge University to work with instructor J.J. Thomson (Campbell). Thomson, who was quick to realize Rutherford’s exceptional ability as a researcher as he had already designed several original experiments involving high-frequency, alternating currents, invited him to become a member of the team to study of the electrical conduction of gases. The pair soon became not only researcher and student but also good friends, and Rutherford was able to take Thomson’s theories and improve on them, breaking the ground to make a lasting impression on nuclear physics today. Rutherford developed several ingenious techniques to study the mechanism Thomson was using, whereby normally insulating gases became electrical conductors. In studying this matter, Rutherford commented that when a high voltage is applied across them, a clear view was given of the mechanism of the transport of electricity through the gases by the means of charged ions (Rutherford 1904). He also worked jointly with Thomson on the behavior of the ions observed in gases that had been treated with X-rays (a recent discovery), as well as the mobility of ions in relation to the strength of the electric field. It did not hurt in any way that Thomson was the one to discover that the “atom”, then known as the smallest unit of matter, was not in fact the smallest, but made up of even smaller particles, giving yet another area of interest for Rutherford to experiment with (Mahanti, 2011). When the Macdonald Chair of Physics at McGill University in Montreal became vacant in 1898, Rutherford left for Canada to take up the post. He promptly made a name for himself by discovering the element of radon, a chemically inactive but extremely radioactive gas (Campbell). While at McGill, he also did the work that gained him the 1908 Nobel Prize in Chemistry by demonstrating that radioactivity was the spontaneous disintegration of atoms. With the help of a young chemist, Frederick Soddy, he began to unravel the mysteries of radioactivity and contributed directly to nuclear physics as we know it today by proving that some heavier radioactive elements spontaneously decay into slightly lighter atoms (Mahanti, 2011). In this, Rutherford noticed that in a sample of radioactive material, it invariably took the same amount of time for half the sample to decay - its “half-life” - and created a practical application for this phenomenon using this constant rate of decay as a clock after monitoring the sequence of decay several times and coming up with the same result each time (Mahanti, 2011). In 1904, Rutherford authored a book called Radio-Activity, in which he set out his principles and theories, noting that the term “radioactive” was generally applied to a class of substances, such as uranium, thorium, radium, and their compounds. This was due to the fact that these elements, and their compounds, possessed the property of spontaneously emitting radiations capable of passing through plates of metal and other ordinary substances opaque to light (Rutherford, 1904). He also noted that the most remarkable property was that the radioactive substances were able to spontaneously and continuously radiate energy at a constant rate, without any outside action being put upon them. This book, the first textbook of its kind, detailed his discoveries up to that point and would define the field of physics for years to come (Mahanti, 2011). Another contribution by Rutherford to nuclear physics was that, in 1898, he discovered and defined two distinct radioactive rays, alpha and beta. Along with the later discovery of gamma rays, in his 1907 book Radioactive Substances and Their Radiations, Rutherford defined and compared them characteristically. Rutherford, while not discovering radiation (that honor went to Henri Becquerel in 1896), was able to build upon the work of the founder as well as subsequent research by Pierre and Marie Curie (Mahanti, 2011). Through experimentation, both by observing whether the rays were “appreciably deflected” in both a magnetic and an electrical field, along with comparing the relative absorption of the rays by solids and gases, he was able to differentiate and give characteristics to each type of radiation (Rutherford, 1907). He noted that alpha particles, termed ?, were readily absorbed by thin metal foil, and consisted of a few positively charged atoms of helium projected at 1/15 the velocity of light. Beta particles, designated ?, were far more penetrating, far more deflecting, and were projected with velocities equal to that of the velocity of light. Gamma rays, designated ?, were extremely penetrating, as well as non-deviable by an electric or magnetic field (Rutherford, 1907). Rutherford's experiments showed that the gamma-rays were a type of X-ray, and that the alpha- and beta-rays were tiny particles of matter, while also showing that the beta-particles were electrons, but the alpha-particles were something new (Cavendish Laboratory). Rutherford continued his work with alpha particles, and in 1907 transferred to Manchester University, where he made at least two more important contributions to nuclear physics. First, he discovered that the alpha particles that he had been postulating about here actually helium ions (Mahanti, 2011). In 1908 he demonstrated this with a clever piece of apparatus. Rutherford made an air-tight glass tube with very thin walls, and filled it with the radioactive radium emanation (Cavendish Laboratory). Alpha-particles could penetrate the thin walls of the tube and were collected in a second tube, and after some time these alpha-particles were compressed and a spark passed. The spectrum of the gas showed that the alpha-particles were helium ions (Cavendish Laboratory). He and an assistant, Hans Geiger, developed the electrical method of tirelessly detecting single particles emitted by radioactive atoms, the Rutherford-Geiger detector. With this he could determine important physical constants such as Avogadro's number, the number of atoms or molecules in one gramme-mole of material (Campbell). The second important contribution was the discovery of what alpha particles actually did, commonly known as Rutherford’s “gold foil experiment”. In 1911, Rutherford recommended to both Geiger and another young student, Ernest Marsden, an experiment that would in the end change not only the findings about alpha particles, but also their very way of thinking. While at McGill, Rutherford had noted that alpha particles became fuzzy in passing through a sheet of mica, and wished Geiger and Marsden to carry out an experiment that would measure the number of alpha particles as a function of scattering angles, in addition to seeing whether or not they were reflected from certain metals (Campbell). In carrying out the experiment, Geiger and Marsden shot alpha particles at a very thin piece of gold foil, in vacuum, and expected to find that most of the alpha particles travel straight through the foil with little deviation, with the remainder being deviated by a percent or two (Davidson, 1996). This thinking was based on the theory that positive and negative charges were spread evenly within the atom and that only weak electric forces would be exerted on the alpha particles that were passing through the thin foil at high energy (Davidson, 1996). To their surprise they found that most of the alpha particle passed through the gold foil in a straight line, some passed through the gold foil but changed their direction slightly and a small number (1 in 8000 particles) actually bounced back (Davidson, 1996). Based on this experiment Rutherford concluded that the atom must be mainly empty space and that the positive charge was not spread out but it was located in the centre. Rutherford describing his astonishment at the results wrote: “It was quite the most incredible event that ever happened to me in my life. It was as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backwards must be the results of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the mass of the atom was concentrated in a minute nucleus.” (Davidson, 1996) Because alpha particles have about 8000 times the mass of an electron and impacted the foil at very high velocities (Cavendish Laboratory), it was clear to all three men that very strong forces were necessary to deflect and backscatter these particles. Rutherford explained this phenomenon with a revitalized model of the atom in which most of the mass was concentrated into a compact nucleus (holding all of the positive charge), with electrons occupying the bulk of the atom's space and orbiting the nucleus at a distance (Campbell). This came to be known as the “nuclear” model of the atom. With the atom being composed largely of empty space, it was then very easy to construct a scenario where most of the alpha particles passed through the foil, and only the ones that encountered a direct collision with a gold nucleus were deflected or scattered backwards. It was in these experiments that Rutherford made not only important, but lasting contributions to nuclear physics by discovering the nature of the atom, alongside his previous discoveries and research work into radiation, radioactivity, and alpha, beta, and gamma rays. With the help of Niels Bohr, a young Dane, Rutherford was able to carry his own discoveries and research even further. Bohr placed the electrons in stable formation around the atomic nucleus (Campbell). The Rutherford-Bohr atom features in chemistry and physics books used world-wide and Rutherford scattering is still used today to probe sub-nuclear particles and the structure of micro-electronic devices (Campbell). It is ironic that, at times, Rutherford is credited with something that he did not do. Whether it is because most people do not understand the terminology or because Rutherford’s brilliance almost cannot be equaled in the field of nuclear physics is not known, but Rutherford did not split the atom. The atom was unknowingly split when people first made chemical reactions (because that often involves the transfer of electrons from one atom to another), when physicists first made electrical discharges in gases and when scientists first demonstrated electrolysis. J.J. Thomson demonstrated the first evidence of the existence of bodies smaller than the atom when he discovered the electron in 1897 (Campbell). Ernest Rutherford spent two years helping Thomson with experiments on the conduction of electricity in gas discharges so was an instant convert to bodies smaller than atoms with an issue, but the fact remains, he did not split the atom (Campbell). Rutherford was, however, first person to knowingly split the nucleus, in 1919 at Manchester University where he bombarded nitrogen with naturally occurring alpha particles from radioactive material and observed a proton emitted with energy higher than the alpha particle, along with the nitrogen having been converted to oxygen (Campbell). In doing this, he showed that a small amount of hydrogen could be produced (Cavendish Laboratory). He continued in this vein into 1920, having speculated that the nucleus of an atom contained a mass of neutral charge, about the same mass as a proton. Rutherford also speculated that, being of neutral charge, it could easily penetrate the nuclei of an atom (Campbell). It was during this year that he began to look for them, and in 1932, finally succeeded. Rutherford, along with his assistant James Chadwick, finally found solid and substantiated proof of neutral particles inside the nucleus when Chadwick found that he could produce these 'neutrons' by bombarding beryllium with alpha-particles (Cavendish Laboratory). A few months later Ernest Cockcroft and J.D. Walton, who had been working on high voltage accelerators for several years, successfully “split atoms” of lithium using accelerated protons. This earned everyone, including Rutherford (as it was his suggestions that formed the basis of the research) notoriety as it was the first nuclear disintegration that was completely under the control of the experimenter (Campbell). Both experiments gave firm support to Rutherford's belief that nuclei are made up of smaller particles. For years Rutherford had assumed that to penetrate the nucleus of an atom one would need particles accelerated through a few million volts to match the energy with which particles were ejected from radioactive atoms. The breakthrough though came from George Gamow's application of quantum mechanics to show that lower energies would be more efficient at penetrating the atomic nucleus (Campbell). After Cockcroft and Walton's success, Rutherford had Mark Oliphant build a lower voltage accelerator but with a much improved particle flux. Following the gift of heavy hydrogen (deuterium) from Gilbert Lewis of Berkeley, they bombarded deuterium with deuterium and discovered tritium (H3 the third isotope of hydrogen) and the light isotope of helium (He3), another radical discovery and contribution to nuclear physics as we know it today (Campbell). By the time of his death in 1937 from a strangulated hernia, Rutherford had already been given top honors at several universities, in addition to having won a Nobel Prize for Chemistry. His contributions through is research were important, groundbreaking, and lasting well into the physics textbooks used today. He worked tirelessly to make sure that his questions were answered, and showed no fear of experimentation. His work formed the basis of many other discoveries. Rutherford has been noted to be many things, above all the father of nuclear physics. His work and accomplishments have been compared by virtually every past and modern-day researcher in the field of physics to what Darwin did for evolution, Einstein to relativity, and Newton to mechanics. A lesser man might have been satisfied with one accomplishment, but Rutherford was not. There can be no doubt as to his lasting contributions to the field of nuclear physics. Sources: Campbell, J. (n.d.). Rutherford: a brief biography. Retrieved from http://www.rutherford.org.nz/biography.htm#otherbios Cavendish Laboratory.(n.d.). Cambridge physicists: ernest rutherford. Retrieved from http://www-outreach.phy.cam.ac.uk/camphy/physicists/rutherford_prelim.htm Davidson, M. (1996, June 15). Molecular expressions: the rutherford experiment. Retrieved from http://micro.magnet.fsu.edu/electromag/java/rutherford/ Mahanti, S. (2011, April 24). Ernest rutherford: the newtonian of physics. Retrieved from http://www.vigyanprasar.gov.in/scientists/ERutherford.htm Rutherford, E. (1904). Radio-activity [First Edition]. (Online Reader Version), Retrieved from http://www.archive.org/stream/radioactivity00ruthgoog#page/n5/mode/2up Rutherford, E. (1907). Radioactive substances and their radiations (Online Reader Version), Retrieved from http://www.archive.org/stream/radioactivesubs00ruthgoog#page/n6/mode/2up Read More