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An Electron in an Atom Can Be Briefly Replaced with Another Particle Lawrence Berkeley National Laboratory Recent Work Title EXOTIC ATOMS Permalink https://escholarship.org/uc/item/3r01m0fc Author Wiegand, Clyde E. Publication Date 1972-11-01 eScholarship.org Powered by the California Digital Library University of California Published by Scientific American LBL-1517 227, No.5, pp.102-110, 1972 r: , EXOTIC ATOMS Clyde E. Wiegand November 1972 .Prepared for the U.S. Atomic Energy Commission under Contract W -7405 -ENG-48 · For Reference Not to be taken from this room DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completene"ss, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. " ! SCIENTIFIC an Article from l AMERICAN I w0 >a: w w "'a: 1-"' ~ ;:" NOVEMBER, 1972 VOL. 227, NO. 5 0 liii: - • w~ 0 >"' g" @ 1- ~ ;: "> ~ 8 products using a consistent interface system, so that all instruments, no matter what their function, can be Software controlled by connecting them to a common intercon­ Operator necting cable. Thanks to low-cost integrated circuits, Communi­ even inexpensive instruments can have the new inter­ ... cations face, and the cost of an automatic system need be little more than the sum of the costs of the instrument in it. Instruments interconnected through the new Output interface communicate on a " take turn " basis: (one talks Terminals while the others listen). The benefits: ·Low-cost systems can be assembled with no special interface equipment. ·System management can range from simply one instrument controlling another, up through control by calculators and computers. ·System operation is simplified since control can be passed from one device to another. ·The system is flexible in speed, language, and size. Messages and data can be transr]litted at up to one megabyte rates. Stimulus/ Response Additional Memory Making the computer fit your problems. The problem with many computer systems is that you have to make too many trade-offs between what the system can do and what you want to have done. We believe you should have freedom to tackl.e problems your way, and not be forced to accept some­ one else's methodology. So Hewlett-Packard computers and systems are designed to help you be the master of how they"re ·configured and used. With HP's versatile 2100 computer, you can assemble a system thars right for your job. 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Finally, every element of an HP computer system is fully supported from 172 sales and service offices in 65 For more information on the products described in these countries. After the warranty, we can continue to main­ pages, fill out the coupon or write to: Hewlett-Packard, tain your system under a customer service agreement, 1502 Page Mill Road, Palo Alto, California 94304; or show you how to do it yourself. Europe: P.O. Box 85, CH-1217 Meyrin 2, Geneva, · Basically, irs all up to you. And most of our cus­ Switzerland; Japan: Yokogawa-Hewlett-Packard, tomers wouldn't have it any other way. Information on 1-59-1 ,Yoyogi, Shibuya-Ku, Tokyo, 151 . the HP 2100 will be sent upon request. The new non-instrument that's HEWLETT PACKARD making measurements easier. Im!J Automated measurements have long been seen as a way - 00218 to improve productivity, both in scientific research and •··••••••···•••••·•••···•••·•··········•· ....•...•.•.• Please send m.e information on the following: in industry. But establishing local centralized control of ( ) HP-35 Calculator I ~ measuring instruments hasn't been easy. Although some () Optacon ( ) HP 2100 Computer progress has been made over the years, each instrument () Interface System typically has its own provision for external control. Assembling several instruments into an automated Name' --------------------------------~--------- system often takes a system expert and a lot of costly Title------------------------------------------- interface equipment in addition to the instruments Company__________ _______________________________ themselves. Address _________________________________________ This picture is now changing fast. Engineers City__________ _________ State _____________ Zip ___ throughout Hewlett-Packard have agreed to design their ·······································~·············· 101 LAV _L I \...A f\_l Vll'l~ ------­KAON IN ORBIT An electron in an atom can be briefly replaced with another particle. The resulting new atom yields information on the nature of the nucleus by Clyde E. Wiegand he atoms of ordinary matter con­ gen atom, and it will therefore be useful sist of a cloud of negatively to briefly consider the properties of the T charged electrons surrounding a hydrogen atom. The model of the atom positively charged nucleus. The simplest proposed by Niels Bohr in 1913 puts of these atoms is hydrogen, with one the electrons in discrete orbits around electron and a nucleus consisting of one the nucleus. An electron can occupy any proton; the most complex is the latest one of these orbits but not the space in element synthesized by nuclear chem­ between. Each orbit is given a number ists, which has 105 electrons and a nu­ called the principal quantum number cleus made up of 105 protons and 157 and designated n. When a hydrogen neutrons. Most atoms are stable in the atom is in its ground state, that is, its sense that they do not spontaneously state of lowest energy, its electron oc­ change their properties. The exceptions cupies the first Bohr orbit, whose prin­ are the natural and man-made radio­ cipal quantum number is 1. The radius active atoms and what are called exotic of the orbit is 5 X I0-9 centimeter. The atoms. In an exotic atom one of the atom can be excited to higher energy electrons is artificially replaced with states by absorbing a photon, or. quan­ an entirely different negatively charged tum of electromagnetic radiation, from particle. Seven negative particles are an external source. The electron jumps capable of substituting for the electron, to another Bohr orbit, and in I0-8 second and so far five of them have been suc­ the atom spontaneously emits a photon cessfully implanted in ordinary atoms. of its own and the elech·on retums to the Although practically all the mass of an ground state. atom resides in the nucleus, the atom's chemical properties are determined by The orbit to which the electron jumps the number and configuration of the depends on the energy of the photon electrons. Until some 30 years ago the absorbed by the atom: a more energetic only elementary pmticles known were photon will cause the electron to jump the proton, the neutron, the electron and to a higher Bohr orbit (for example, to the positron (a positively charged par­ one where n = 4 or n = 5) than a less ticle with the same mass as the electron). energetic photon will. When the energy In the 1940's studies of cosmic rays re­ of the photon is sufficiently great to re­ vealed another class of charged parti­ move the electron completely, the atom cles: the mesons. Mesons are short-lived is said to be ionized. For hydrogen the particles whose mass ranges between energy of ionization is 13.6 electron the mass of the electron and the mass of volts, corresponding to the energy of a the proton (1,840 times the mass of the photon in the far-ultraviolet region of elech·on). The first man-made mesons the electromagnetic spectrum. A lone were the pions, or pi mesons, created in proton will ultimately attract a free elec­ the 184-inch cyclotron at the University tron or steal one from another atom. The of California at Berkeley in 1948. It new hydrogen atom will emit photons as EXOTIC ATOM IS FORMED when one or was several years-and several cyclo­ the freshly ath·acted electron cascades more electrons of an ordinary atom are ar­ tificially replaced with an entirely different trons-later that negative pions were down to the ground state from the orbits negatively charged particle. In this illustra­ successfully substituted for electrons in with large principal quantum numbers. tion the capture of a kaon (K meson) by a atoms.
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