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Ernest 0. Radiation Lawrence Laboratory UCRL-10780 1111111 University of California Ernest 0. lawrence Radiation Laboratory TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Dioision, Ext. 5545 ATOMIC BEAM MEASUREMENTS OF THE NUCLEAR SPINS OF COPPER-62 AND IRON-59 AND THE HYPERFINE-STRUCTURE SEPARATION OF COPPER-61 AND COPPER-64 Berkeley, California 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, completeness, 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. Research and Development UCRL-10780 UC-34 Physics TID -4500 (19th Ed. ) UNIVERSITY OF CALIFORNIA Lawrence Radiation Laboratory Berkeley, California Contract No. W -7405-eng-48 ATOMIC BEAM MEASUREMENTS OF THE NUCLEAR SPINS OF COPPER-62 AND IRON -59 AND THE HYPERFINE-STRUCTURE SEPARATION OF.COPP.ER-'6T AND COPPER-64 Barbara Marie Dodsworth (Ph. D. Thesis) April 18, 1963 • Printed in USA. Price $2.50. Available from the Office of Technical Services U. S. Department of Commerce Washington 25, D.C. iii CONTENTS Abstract .•. v I. Introduction .. 1 II. Atomic Theory . A. The Hamiltonian of an Atom . 3 1. Nuclear Hamiltonian .. 0 0 •. 3 2. Electrostatic Interactions in an Atom .• 3 3· Hyperfine Interaction Term 8 4. Interaction of an Atom with External Field.s . • . 14 B. Nuclear Theory 21 III. Experiment 25 A. Description of the Apparatus . 25 B. lvlethod.s of Detection • 27 c. Experimental Procedure 36 61 IV. Cu Experiment 39 A. Isotope Production and. Chemistry • . • . • • • • . 39 B. Theory of the Cu Experiment • . • . • • , . • . • . 42 1. General Description of Theory • 2. Determination of the Sign of gi . 46 c. Experimental Procedure and Data Ana~sis 48 61 D. Results for Cu 50 v. Cu 62 Exper11nen. t 61 A. Isotope Production and Chemistry 61 B. Experimental Procedure and. Data Analysis 61 62 C. Theory of cu Experiment • . • . • . • . • 63 62 D. Results for Cu . o • • • • • • • • o • • • • • • o • • • 67 iv VI. Cu 64 Ex perJJllen. t 72 A. Isotope Production 72 B. Experimental Procedure and Data Analysis . 72 64 c. Theory of the cu Experiment ....•.... _. 72 D. Results for Cu 64 . 75 VII. Fe59 Experiment 84 A. Beam Production 84 B. Isotope Production and Identification . 93 C . Experimental Procedure . 97 D. Multiple Quantum Transitions in Fe59 97 E. Theory of the Fe59 Experiment •............... 99 F. Results for Fe59 o o o o o o o n o o . o o o • e· o o o o o e . 99 ·VIII. Additional Isotopes 109 6-- A. Cu 1 Experiment . 109 223 B. Fr Experiment . 109 136 C. Cs Experiment 113 IX. Acknowledgements • 115 References . 0 • 0 116 v ATOMIC BEAM MEASUREMENTS OF THE NUCLEAR SPINS OF COPPER-62 .AND IRON-59 AND THE HYPER- FINE-STRUCTURE SEPARP.TION OF COPPER-61 .AND COPPER-64 Barbara Marie Dodsworth Lawrence Radiation Laboratory and Department of Physics J University of California, Berkeley, California . 1,· April 18, 1963 ABSTRACT The atomic beam magnetic resonance method of the "flop-in" type using the technique of radioactive detection has been employed to measure the 62 nuclear spins of cu and Fe59 as well as the byperfine-structure separa­ 61 61 tion of cu , the sign of the moment of cu , and an improved value for the 64 61 6v of cu • The magnetic moment of cu was calculated from the . Fermi-Segr~6 formula, using previously measured values for the 6v and ~I of Cu 3 .- The results of the experimental work, together with calculated values of the nuclear magnetic dipole moments, are Isotope Half-life Spin hfs6v ~I (uncorr) (Mc[sec) {run) ' Cu61 3.3 hours 3/2a 11,400(300) + 2.16(6). Cu62 10 minutes 1 ---- - - - - - ~ Cu64 12.8 hours la 1282.140(20) ± 0.216(2) Fe 59 45 days 3/2 --- - -- -- - - a Measured previously by other workers. 61 The cu isotope was produced on the Berkeley 60-inch cyclotron by the 61 62 reaction co59(a,2n)cu • The cu isotope was also produced on the cyclo- 62 . 62 tron by the decay of Zn formed by the reaction N~(a,2n)Zn • Beth the Cu 64 isotopes \vere chemically separated from the target materials. The Cu was formed by neutron bombardment of copper\ in the Livermore and_Val.lecitos. "·. vi reactors; Fe59 was produced by irradiation with neutrons in~he-ETR reactor ;tn-I-d:a.he • Radioactivity in the beam 'vas measured by expos:i.ng collectors to the beam and counting these "buttons" in either sodium iodide--crystal scintil­ lation counters or continuous-flow methane counters, depending on the mode of decay of the particular isotope. The main boqy of the thesis contains theory of atomic structure, a description of the experimental apparatus and technig:ues employed.. , methods of data analysis, and results. The results are interpreted in terms of simple nuclear shell·-model theory. -· 1 - I. INTRODUCTION I In 1911 Dunoyer (mm 11) initiated the field of research with mole- cu.lar beams by producing a directed beam of neutral molecules at pressures low enough that the effect of molecular collisions could be neglected. The applicability of the beam method to studying properties of atoms and mole­ cules was first recognized by Stern in 1919. These studies later resulted in the Stern-Gerlach experiment (STE 21), w]lich, .for example, proved experimentally the space quantization of angular momentum. The new tech­ nique, utilizing a small oscillating magnetic field. to cause reorientation of the spin or magnetic moment with respect to a constant field, was de­ veloped by Rabi and others (RAB 38). In 191~2, Zacharias (ZAC 42) refined the technique by introducing the "flop.:..in" method. which, in conjunction with the radioactive detection scheme of K. F. Smith (SMI 51), enhanced the signal-to-noise ratio. This method was employed. to measure the nuclear properties of the Cu and·Fe isotopes presented in this thesis and is quantitatively as follOivs; The atoms are heated in a small container called an oven which emits the atoms through a slit on the front. Leaving the oven, the beam passes through a system of collimating slits and. finds itself in an excellent vacuum. Since the mean free path of the atoms is many times the length of the apparatus, very few atoms make collisions during the time of the experi­ ment, i.e., most of them are isolated from one another. Two inhomogeneous magnetic fields, called the A and B fields, are used to deflect the atoms by means of the interaction of the-magnetic moments of the atoms with the grad.ient of the applied magnetic field.. The C field region, betvreen the A and B field.s, consists of a very homogeneous magnetic field plus a small impressed radio-freq~ency field which is capable of inducing transitions between the energy levels of the atom. The rad.io frequency necessary to induce transitions is a function of the strength of the C field, which can be easily measured, and of the atomic and nuclear constants of the atom. If the atom undergoes no transition in the C field, it is deflected in the same d.irection in the B field as it was in the A field and. is "thrown out" away from the detector. If the atom undergoes a transition in.the C field and hence changes the sign of its effective magnetic moment~ its deflection in the B field is opposite to what it was in the A field and the atom is - 2 - focussed. onto the detector, The detector is a sulfur-coated piece of brass which can be removed form the machine and counted in crystal or ~-counters depending on the mode of decay of the radioactive species. The resonance, which is observed as an increase in the counting rate versus frequency, can be used to determine various atomic and nuclear properties--,such as, for ex~ple, the nuclear spin and the hyperfine-structure separation, from which one can deduce the dipole and quadrupole interaction constants. It is also possible to measure the sign of the magnetic moment. The bas~c design and construction of the flop-in atomic beam apparatus used in the following experiments is described in more detail in R. J, Sunderland's (SUN 56), Ph.D. thesis. "' - 3 - II . ATOMIC THEORY A. The Hamiltonian of an Atom One of the main features of atomic beam experiments it that the atoms '"' are isolated from one another because at-low pressures the mean free path for collisions is many times the length of the apparatus. Hence in the absence of external magnetic or electric fields, the interaction terms in the Hamiltonian are all internal to a single atom. According to the nuclear model, one may consider the atom as made up of a central massive positively charged nucleus surrounded by an electron syst·em arranged in the central Coulomb field produced by the nucleus.
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