DOCSLIB.ORG

Interactions 2018

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Interactions 2018 Mellon College of Science | Carnegie Mellon University INTERACTIONS Department of Physics | 2018/2019 CONTENTS INTERACTIONS LETTER FROM DEPARTMENT HEAD, 02 Department of Physics SCOTT DODELSON Interactions is published yearly by the Department of Physics at Carnegie Mellon University for its students, alumni and friends to inform them FACULTY NOTES 03 about the department and serve as a channel of communication for our community. Readers with comments or questions are urged to send them to Interactions. Fax to 412-681-0648 or phone 412-268- 2740. The department is headed by Scott Dodelson. A QUANTUM AGE 14 Editor-in-Chief Scott Dodelson, Department Head Editor Jocelyn Duffy, Associate Dean for Communications Barry Luokkala, Teaching Professor Contributing Writers Joyce DeFrancesco, Jocelyn Duffy, Stephen Garoff, Barry Luokkala, Ben Panko, Emily Payne, Curtis Meyer, Lee Schumacher Graphic Design RESEARCH NOTES Rachel Wadell, Publications Manager 18 and Graphic Designer Photography and Images Courtesy of Carnegie Mellon University, unless otherwise noted Department of Physics Carnegie Mellon University 5000 Forbes Avenue Pittsburgh, PA 15213 www.cmu.edu/mcs/physics STUDENT NOTES 21 Cover photo courtesy of: Gaia Data Processing and Analysis Consortium (DPAC); A. Moitinho / A. F. Silva / M. Barros / C. Barata, University of Lisbon, Portugal; H. Savietto, Fork Research, Portugal. Copyright: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO PHYSICS STUDENTS 24 FIND INSPIRATION AT UNDERGRADUATE CONFERENCE FOR WOMEN Carnegie Mellon University does not discriminate in admission, employment, or administration of its programs or activities on the basis of race, color, national origin, sex, handicap or disability, age, sexual orientation, gender identity, religion, creed, ancestry, belief, veteran status, or genetic information. Furthermore, Carnegie Mellon University does not discriminate and is required not to discriminate in violation of federal, state, or local laws or executive orders. ALUMNI NOTES 30 Inquiries concerning the application of and compliance with this statement should be directed to the vice president for campus affairs, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, telephone 412-268-2056. Obtain general information about Carnegie Mellon University by calling 412-268-2000. DEPARTMENT OF PHYSICS 1 FACULTY NOTES LETTER FROM THE DEPARTMENT OF MANFRED PAULINI ELECTED AS A FELLOW PHYSICS HEAD, SCOTT DODELSON OF THE AMERICAN PHYSICAL SOCIETY 2018 was a year of transition, growth and success in the physics Manfred Paulini, professor of physics and associate dean for faculty and department. In the pages that follow, you will read about awards graduate affairs, has been elected as a fellow of the American Physical received by our alumni, current faculty, graduate students and Society (APS). undergraduates. You will be introduced to our four new faculty Fellows are elected based on their contributions to physics, through members, with interests ranging from discovering the properties of research, application of physics, leadership and service, or their the Higgs boson to the two-dimensional materials that underpin the contributions to physics education. The APS limits the number of fellows second quantum revolution to the theory that encompasses all of this to no more than one-half of one percent of its members. and more. Paulini, who was nominated by the APS Division of Particles and Fields, Please take a look at the section describing the illustrious careers of our was recognized for his leadership in large scale physics experiments and three new emeritus faculty members, but keep in mind that all three are his work connecting particle physics with cosmology. still mainstays of the department and as active as ever. The department has been at the forefront of many of the more important discoveries in As a member of the Collider Detector at Fermilab experiment, Paulini physics in 2018, as you can see on pages 14-20, and is starting a Theory searched for charge conjugation parity symmetry violations in decays of Center that cuts across the Mellon College of Science. neutral B mesons. Finding these violations could yield clues that will help physicists to better understand why matter seems to predominate over In the midst of it all was the horrific attack at the Tree of Life antimatter in the universe. synagogue. Many of us had connections to the institution and some of the victims. All of us were overwhelmed by the outpouring of Paulini is also a member of the Compact Muon Solenoid Detector support from the community, far and wide. While we continue to experiment at the Large Hadron Collider. There, he is searching for mourn for the lives lost, we have come to appreciate more than ever supersymmetric particles — possible candidates to explain dark matter the need to build an inclusive community. in the universe. What better institution to form the basis of a community than a university, one whose mission is to extend the boundaries of knowledge and educate young people to thrive in a rapidly changing world? We are trying hard in the Department of Physics to gather in and build outwards. You can read about the women who attended the Conference for Undergraduate Women in Physics; we are pleased DI XIAO NAMED AMONG WORLD’S to announce that we will host the 2020 version of this very important MOST HIGHLY CITED RESEARCHERS event. We are planning to start an “Everyone Counts” outreach program: every member of the department will participate, and we will attempt to reach students from ages 5 to 95, from those who are Di Xiao, associate professor of physics, was listed among the most waiting to be inspired by the beauty of physics to those who need highly cited researchers in the field of physics by Clarivate Analytics. a helping hand in a tough economy to seniors looking for a window Xiao’s publications were in the top one percent of the most cited papers into the world of active research. in the field and indexed in the Web of Science, which is operated by Please join our community: feel free to visit, chat and attend lectures; Clarivate Analytics. talk to our students about their career options; and — if you have the Xiao’s research looks at the properties of materials in relation to means — support our efforts to train the next generation of scientists quantum mechanics and how these properties can be harnessed for Banner Image: Courtesy of G. Torrealba (Academia and empower them to work with state-of-the-art equipment. applications in electronic and magnetic devices. Sinica, Taiwan), V. Belokurov (Cambridge, UK and CCA, We wish you all a wonderful holiday season and a happy, healthy This year’s list includes roughly 4,000 highly cited researchers in 21 fields New York, US) based on the new year. of the sciences and social sciences and 2,000 cross-field researchers. image by ESO/S. Brunier 2 INTERACTIONS FACULTY NOTES 3 Hael Collins and Stephen Garoff Win Mellon College of Science Awards for Education Julius Ashkin Teaching Award: Hael Collins The Richard Moore Award: Stephen Garoff Department of Physics Special Faculty Professor of Physics Stephen Garoff has Lecturer Hael Collins won the Mellon College been honored with the Mellon College of of Science 2018 Julius Ashkin Teaching Award Science 2018 Richard Moore Award. This for his devotion and effectiveness in teaching. award is presented every year to a faculty Collins manages to strike a perfect balance member in the college who is making between challenging his students — pushing substantial and sustained contributions them to perform beyond what they believe to the educational mission of the college, themselves capable of — and having them particularly when those contributions have appreciate him for it. extended over a significant portion of their academic career. Collins has managed this feat with an extraordinary range of students, from non- Garoff has been a member of the science majors with a limited background in Department of Physics for over three the physical sciences to graduate students decades, and in that time, he has been working in the most advanced and narrow instrumental in shaping both the topics in the field; at every level, he receives department and MCS as a whole. He rave reviews. advocated for interdisciplinary cooperation and research between departments, helping “I feel he went above and beyond in his effort to implement courses such as Physics I for putting this course together, and the class as Engineering Students and Physics II for a whole reaped the benefits of this, enjoying Biological Sciences and Chemistry Majors. the experience of a very challenging and perhaps equally rewarding course,” said one Along with his colleagues, Richard Edelstein former student of Collins’ Introduction to and Reinhard Schumacher, Garoff developed Nuclear and Particle Physics course. the Modern Physics Laboratory, which has become a highlight of the undergraduate Collins has taught an impressive 13 different curriculum. He has striven to design curricula courses in the past seven years. Students that emphasize real-world applications of profess their appreciation for both his classroom material and prepare students to teaching style and the rigorous content of his succeed after graduation. classes. He balances difficult and unrelenting coursework with subtle humor, genuine care Garoff has been unrelentingly dedicated to and a significant amount of extra time to the education of MCS students. He served prepare additional study materials. as advisor to dozens
Load more

Recommended publications
  • Electron Diffraction V2.1
    Electron Diffraction v2.1 Background. This experiment demonstrates the wave-like nature of an electron as first postulated by Louis de Brogile in 1924. All particles including electrons have a wavelength inversely related to momentum: l = h/p. (1) It was well known at the time that the light could be diffracted by a periodic grating, where the grating period is of the order of the electromagnetic wavelength. If an electron has wave properties, then there might be a suitable physical grating to diffract it. Max von Laue had first suggested that periodic planes of atoms in a solid could serve as a grating. X- ray reflection experiments of Lawrence Bragg confirmed this and gave an estimate of the inter- Davisson and Germer in 1927 atomic spacing. Planes of atoms in a solid can also provide the appropriate grating spacing to cause electron diffraction. In a Nobel Prize winning experiment at Bell Labs in New Jersey, Clinton Davisson and Lester Germer used crystalline nickel to diffract electrons and prove their existence as waves. An independent experiment was done around the same time by George Thomson in Scotland. This was foundational work for the transmission electron microscope (TEM). The present experiment uses an ultra-thin polycrystalline graphite layer in place of nickel as the diffraction grating. Graphite forms as single planes of carbon atoms in a hexagonal arrangement shown in Figure 1. Vertical planes are not chemically bonded to adjacent planes. Instead they are more loosely held by the electrostatic van der Waals force but the atoms are remain aligned vertically.
    [Show full text]
  • 1 the Principle of Wave–Particle Duality: an Overview
    3 1 The Principle of Wave–Particle Duality: An Overview 1.1 Introduction In the year 1900, physics entered a period of deep crisis as a number of peculiar phenomena, for which no classical explanation was possible, began to appear one after the other, starting with the famous problem of blackbody radiation. By 1923, when the “dust had settled,” it became apparent that these peculiarities had a common explanation. They revealed a novel fundamental principle of nature that wascompletelyatoddswiththeframeworkofclassicalphysics:thecelebrated principle of wave–particle duality, which can be phrased as follows. The principle of wave–particle duality: All physical entities have a dual character; they are waves and particles at the same time. Everything we used to regard as being exclusively a wave has, at the same time, a corpuscular character, while everything we thought of as strictly a particle behaves also as a wave. The relations between these two classically irreconcilable points of view—particle versus wave—are , h, E = hf p = (1.1) or, equivalently, E h f = ,= . (1.2) h p In expressions (1.1) we start off with what we traditionally considered to be solely a wave—an electromagnetic (EM) wave, for example—and we associate its wave characteristics f and (frequency and wavelength) with the corpuscular charac- teristics E and p (energy and momentum) of the corresponding particle. Conversely, in expressions (1.2), we begin with what we once regarded as purely a particle—say, an electron—and we associate its corpuscular characteristics E and p with the wave characteristics f and of the corresponding wave.
    [Show full text]
  • INDUSTRIAL STRENGTH by MICHAEL RIORDAN
    THE INDUSTRIAL STRENGTH by MICHAEL RIORDAN ORE THAN A DECADE before J. J. Thomson discovered the elec- tron, Thomas Edison stumbled across a curious effect, patented Mit, and quickly forgot about it. Testing various carbon filaments for electric light bulbs in 1883, he noticed a tiny current trickling in a single di- rection across a partially evacuated tube into which he had inserted a metal plate. Two decades later, British entrepreneur John Ambrose Fleming applied this effect to invent the “oscillation valve,” or vacuum diode—a two-termi- nal device that converts alternating current into direct. In the early 1900s such rectifiers served as critical elements in radio receivers, converting radio waves into the direct current signals needed to drive earphones. In 1906 the American inventor Lee de Forest happened to insert another elec- trode into one of these valves. To his delight, he discovered he could influ- ence the current flowing through this contraption by changing the voltage on this third electrode. The first vacuum-tube amplifier, it served initially as an improved rectifier. De Forest promptly dubbed his triode the audion and ap- plied for a patent. Much of the rest of his life would be spent in forming a se- ries of shaky companies to exploit this invention—and in an endless series of legal disputes over the rights to its use. These pioneers of electronics understood only vaguely—if at all—that individual subatomic particles were streaming through their devices. For them, electricity was still the fluid (or fluids) that the classical electrodynamicists of the nineteenth century thought to be related to stresses and disturbances in the luminiferous æther.
    [Show full text]
  • Quantum Interference of Molecules--Probing the Wave Nature of Matter
    Anu Venugopalan is on the faculty of the School of Basic and Applied Sciences, GGS Indraprastha University, Delhi. Her primary research interests are in the areas of Foundations of Quantum mechanics, Quantum Optics and Quantum Information. Address for Correspondence: University School of Basic and Applied Sciences, GGS Indraprastha University Kashmere Gate, Delhi - 11 0 453 e-mail: [email protected] arXiv:1211.3493v1 [physics.pop-ph] 15 Nov 2012 1 Quantum Interference of Molecules - Probing the Wave Nature of Matter Anu Venugopalan November 16, 2012 Abstract The double slit interference experiment has been famously described by Richard Feynman as containing the ”only mystery of quantum mechanics”. The history of quantum mechanics is intimately linked with the discovery of the dual nature of matter and radiation. While the double slit experiment for light is easily undert- sood in terms of its wave nature, the very same experiment for particles like the electron is somewhat more difficult to comprehend. By the 1920s it was firmly established that electrons have a wave nature. However, for a very long time, most discussions pertaining to interference experiments for particles were merely gedanken experiments. It took almost six decades after the establishment of its wave nature to carry out a ’double slit interference’ experiment for electrons. This set the stage for interference experiments with larger particles. In the last decade there has been spectacular progress in matter-wave interefernce experiments. To- day, molecules with over a hundred atoms can be made to interfere. In the following we discuss some of these exciting developments which probe new regimes of Nature, bringing us closer to the heart of quantum mechanics and its hidden mysteries.
    [Show full text]
  • An Explanation of the Double Slit Experiment Based on the Circles Theory
    Quantum Speculations 3 (2021) 33 - 52 Original Paper An Explanation of the Double Slit Experiment Based on the Circles Theory Mohammed Sanduk* Department of Chemical and Process Engineering, University of Surrey, Guildford, GU2 7XH, UK * Author to whom correspondence should be addressed; E-mail: [email protected] Received: 27 December 2020 / Accepted: 25 March 2021 / Published online: 31 March 2021 Abstract: The circles theory tries to explain the complex functioning of the harmonic oscillator. It is a non-quantum mechanics theory, but it shows a good similarity with the forms of equations of the relativistic quantum mechanics. The Circles Theory explains the association of the wave and the point that corresponds with the wave and particle of quantum mechanics. According to the circular motions of an individual system, a fluid model for a huge number of the circular system is expected to be formed. Then, a wave of fluid may appear. So, a real wave of fluid-type is seen due to the circular motion in addition to the wave associated with the point or the particle. In this article, the double slit experiment has been explained in accordance with the circles theory. According to the circles theory, the double slit experiment shows that this fluid-like wave is responsible for the interference pattern, whereas the associate wave is responsible for the uncertain location of the particle on the screen. On the other hand, the observation of the fluid may destroy the formulation of the wave of fluid. If this happens, then the interference disappears, but a pattern of shout bullets appears.
    [Show full text]
  • Deciphering the Enigma of Wave-Particle Duality Mani Bhaumik1 Department of Physics and Astronomy, University of California, Los Angeles, USA 90095
    Deciphering the Enigma of Wave-Particle Duality Mani Bhaumik1 Department of Physics and Astronomy, University of California, Los Angeles, USA 90095 A reasonable explanation of the confounding wave-particle duality of matter is presented in terms of the reality of the wave nature of a particle. In this view a quantum particle is an objectively real wave packet consisting of irregular disturbances of underlying quantum fields. It travels holistically as a unit and thereby acts as a particle. Only the totality of the entire wave packet at any instance embodies all the conserved quantities, for example the energy-momentum, rest mass, and charge of the particle, and as such must be acquired all at once during detection. On this basis, many of the bizarre behaviors observed in the quantum domain, such as wave function collapse, the limitation of prediction to only a probability rather than a certainty, the apparent simultaneous existence of a particle in more than one place, and the inherent uncertainty can be adequately understood. The reality of comprehending the wave function as an amplitude distribution of irregular disturbances imposes the necessity of acquiring the wave function in its entirety for detection. This is evinced by the observed certainty of wave function collapse that supports the paradigm of reality of the wave function portrayed in this article. 1. Introduction Ever since the advent of the wildly successful quantum theory nearly a century ago, its antecedent, wherein the wave aspect is always associated with a particle has been a source of great mystery to professional scientists and to the public as well.
    [Show full text]
  • Lecture 35 (De Broglie & Matter Waves)
    Lecture 35 (de Broglie & Matter Waves) Physics 2310-01 Spring 2020 Douglas Fields Symmetry • I’ve talked about symmetry in physics a lot… – The symmetry of the Maxwell’s equations in E and B (in vacuum, at least). – The symmetry of space and time in special relativity. – Many others • But the initial development of Quantum Mechanics is a beautiful example of how one can use symmetry to theorize something that has yet to be observed. • This was done by Louise-Victor de Broglie in his PhD thesis of 1924… Particle Waves • De Broglie hypothesized that since light waves behave like particles, perhaps particles should also behave like waves. • Since, for light: • Then, the same should also hold true for matter (or particles). • Hence, for a particle: • Which, of course, reduces in the limit of low v to: Particle Waves • Similarly, the frequency of a photon is given by its energy: • So, for a particle: • And, again, at low v, this reduces to: Overall phase factor that cancels in all physics measurements Particle Waves • So, from analogy with light, de Broglie postulated that: • So, let’s see if this gives us the correct velocity of the particle… Periodic Wave Description • Remember: y x Wave travelling to the right Periodic Wave Description • How fast is the wave moving? y x Wave Velocity • Let’s look at this in relation to what we (should) know about wave motion. • Since we know that the velocity of a wave is given by the angular frequency ω and wave number k, let’s calculate these: • And we take our normal way of finding the velocity of a wave: • Crap.
    [Show full text]
  • I Don't Understand Quantum Physics
    I Don't Understand Quantum Physics by Douglas Ross FRS Emeritus Professor of Physics, University of Southampton i Contents 1 Introduction - Understanding \understanding". 1 2 Some Classical Physics 3 2.1 Waves .......................................3 2.1.1 Interference and Diffraction . .4 2.1.2 Wavepackets . .5 2.1.3 Travelling and Standing Waves . 14 2.2 Particles . 15 3 Experiments that Shook the World of Physics. 22 3.1 The Ultraviolet Catastrophe . 22 3.2 The Photoelectric Effect. 25 3.3 Compton Scattering . 27 3.4 Bragg X-ray Diffraction . 29 3.5 The Davisson-Germer Experiment . 30 4 Wave-Particle Duality 34 4.1 Both a wave and a particle . 34 4.2 Which Slit did the particle go through? . 35 5 What is a Matter (de Broglie) Wave? 37 6 Particles and Fields 39 7 Heisenberg's Uncertainty Principle 41 8 Wavefunctions - Schr¨odinger'sEquation 44 8.1 Discrete Energy Levels . 44 8.1.1 Particle in a Box (in one dimension) . 44 8.1.2 Harmonic Oscillator . 46 8.1.3 The Hydrogen Atom . 47 ii 9 Quantum Tunnelling 51 10 Quantum States and Superposition 53 11 Two State Systems 55 11.1 Photon Polarization . 55 11.2 Electron Spin . 57 12 Wavefunction Collapse 61 12.1 Decoherence . 62 13 Interpretations of Quantum Physics 64 13.1 Copenhagen Interpretation . 64 13.2 Many Worlds Interpretation. 64 14 Two Enigmatic \Thought Experiments" 66 14.1 Schr¨odinger'sCat . 66 14.2 Einstein Rosen Podosky (EPR) Paradox - entanglement . 68 15 Hidden Variables 71 16 Why is the Quantum World so Small? 76 17 Probabilistic Determinism 78 18 Is Quantum Theory Correct and Complete? 80 iii Acknowledgments I am extremely grateful to Laurence Baron, Alexander Belyaev, Jean-Michel Jakobow- icz, David Pugmire, Joe Stroud and Anthony Warshaw for reading earlier versions of this manuscript and making a number of helpful suggestions for improving the clarity of the text.
    [Show full text]
  • Crystallographic Career of Sidney Cyril Abrahams
    Sidney Cyril Abrahams was a crystallographer at Bell Labs for 31 years, a charter member of the ACA and its president in 1968. As part of the ACA History Project, he describes here his career as a crystallographer, also as editor of Acta Crystallographica. Sidney’s full narrative will be deposited at the Center for the History of Physics (AIP). This article is part of an ongoing series by individual crystallographers. If you would like to contribute your story, contact Virginia Pett, [email protected]. Born May 28, 1924 in London, England and educated at Ilford County High School 1935-1938 and Greenock Academy 1938-1942, the present writer graduated BSc with first class honors in chemistry from the University of Glasgow in 1946, where J. Monteath Robertson was Gardiner Professor of Chemistry. Entering graduate school under the supervision of JM, a pioneer of X-ray crystallography, was a “no brainer”. Working at the Royal Institution with such major figures as W. H. Bragg, W. T. Astbury, J. D. Bernal and K. Lonsdale, JM had become a founder of organic crystallography, an area in which he played a major role by his development of heavy-atom and isomorphous-replacement methods for solving the phase problem. JM’s research group in 1946 included Jack D. Dunitz, A. (Sandy) McL. Mathieson and John G. White, each of whom subsequently made valuable contributions to structural crystallography. In 1948, the summer before completing his PhD thesis, the writer received an invitation to participate in Massachusetts Institute of Technology’s coming summer term as one of 62 graduate students from 18 different European countries, four of whom were from the United Kingdom.
    [Show full text]
  • Davisson – Germer Experiment Announcements: • Homework Set 5 Is Today
    Davisson – Germer experiment Announcements: • Homework set 5 is today. • Homework set 6 will be posted later today. • Made a good guess about the Nobel Prize for 2013 Clinton Davisson and Lester Germer. Davisson won Nobel Prize in 1937. Germer didn’t! – No dynamite money! Today we will go over the Davisson-Germer experiment. http://www.colorado.edu/physics/phys2170/ Physics 2170 – Fall 2013 1 Lester Germer • Born on October 10, 1896, graduated from Cornell University in 1917. After graduation he joined Bell Labs and then served in World War I as a fighter pilot, earning a citation from General Pershing. After the war he returned to Bell Labs and finished his Ph.D. at Columbia University in 1927. • At Bell Labs, Germer initially worked as an assistant to Clinton Davisson. In April of 1925 Davisson and Germer began working on an experiment studying the diffraction of electrons off of a nickel surface. At first their results were similar to results obtained four years earlier. Then suddenly the results changed. http://www.colorado.edu/physics/phys2170/ Physics 2170 – Fall 2013 2 Germer cont. • They performed a similar experiment in 1927, after Davisson had attended a conference where DeBroglie's hypothesis about the wave nature of matter was presented. When electrons of known velocity were used to bombard the nickel surface at a 45 degree angle they observed that the diffraction of the electrons obeyed Bragg's Law. This was the first proof of DeBroglie's particle wave hypothesis. • After this experiment Germer continued working at Bell Labs, studying the use of this technique to determine the structure of surfaces, work that eventually led to the development of the electron microscope.
    [Show full text]
  • Syllabus & Lecture Notes
    1 I. SYLLABUS AND INTRODUCTION Let us start with a brief overview of the items that will (hopefully) be covered in this course and to give a guideline of what we are trying to learn. Quantum mechanics 660 and 661 are advanced quantum mechanics courses designed for graduate students. The courses will be treated as a one-year course. It will be assumed that students have already some background in quantum mechanics (the concepts of waves, quantization, expectation values, etc.). An advised introductory text- book is Introduction to quantum mechanics by Griffiths. A number of things will, however, be repeated albeit in a more mathematical fashion. Also some basic knowledge in Fourier analysis, differential equations and linear algebra (calculation of eigenvalues and eigenstates) will be expected. All the information you need to know are in the lecture notes. However, the lecture notes are relatively concise and further reading is recommended. The book that was used last year was Liboff, Introductory Quantum Mechanics, fourth edition. However, a lot of other books treat the material of 660 in a similar fashion, so pick a book that you like best. Some of the material is not covered in Liboff (the older editions don’t have relativistic quantum mechanics and quite a bit of the material of 661 is not in there). The course is developed from a physicists point of view. Some concepts and mathematical techniques will be intro- duced along the way (such as matrix techniques) under the assumption that most of you are already somewhat familiar with them (after all, there are also 3 and 4 hundred level quantum mechanics courses).
    [Show full text]
  • Atomic and Nuclear Physics Physics
    LD Atomic and Nuclear Physics Physics Introductory experiments Leaflets P6.1.5.1 Dualism of wave and particle Diffraction of electrons in a polycrystalline lattice (Debye-Scherrer diffraction) Objects of the experiment g Determination of wavelength of the electrons g Verification of the de Broglie’s equation g Determination of lattice plane spacings of graphite Principles Louis de Broglie suggested in 1924 that particles could have wave properties in addition to their familiar particle properties. He hypothesized that the wavelength of the particle is in- versely proportional to its momentum: h λ = (I) p λ: wavelength h: Planck’s constant D1 p: momentum His conjecture was confirmed by the experiments of Clinton Davisson and Lester Germer on the diffraction of electrons at crystalline Nickel structures in 1927. In the present experiment the wave character of electrons is demonstrated by their diffraction at a polycrystalline graphite lattice (Debye-Scherrer diffraction). In contrast to the experi- ment of Davisson and Germer where electron diffraction is observed in reflection this setup uses a transmission diffrac- tion type similar to the one used by G.P. Thomson in 1928. From the electrons emitted by the hot cathode a small beam is singled out through a pin diagram. After passing through a focusing electron-optical system the electrons are incident as sharply limited monochromatic beam on a polycrystalline D graphite foil. The atoms of the graphite can be regarded as a 2 space lattice which acts as a diffracting grating for the elec- trons. On the fluorescent screen appears a diffraction pattern of two concentric rings which are centred around the indif- fracted electron beam (Fig.
    [Show full text]