NBS'!’-B NSRDS-NBS 14 lKS»SS VIA.'*7 C_’ —“ ;S!?f NBS PUBLICATIONS X-Ray Wavelengths and X-Ray Atomic Energy Levels U.S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS —.'..c-s i t>o .U573 H&.W — National Standard Reference Data Series National Bureau of Standards National Standard Reference Data System. Plan of Operation, NSRDS-NBS 1—15 cents* Thermal Properties of Aqueous Uni-univalent Electrolytes NSRDS-NBS 2—45 cents* Selected Tables of Atomic Spectra, Atomic Energy Levels and Multiplet Tables—Si n. Si hi, Si iv, NSRDS—NBS 3, Section 1—35 cents* Atomic Transition Probabilities, Volume I, Hydrogen Through Neon, NSRDS-NBS 4 $2.50* The Band Spectrum of Carbon Monoxide, NSRDS-NBS 5—70 cents* Tables of Molecular Vibrational Frequencies. Part 1, NSRDS-NBS 6—40 cents* High Temperature Properties and Decomposition of Inorganic Salts. Part 1. Sulfates, NSRDS-NBS 7—35 cents* Thermal Conductivity of Selected Materials. NSRDS-NBS 8—$1.00* Tables of Biomolecular Gas Reactions. NSRDS-NBS 9—In press Selected Values of Electric Dipole Moments for Molecules in the Gas Phase. NSRDS- NBS 10—In press Tables of Molecular Vibrational Frequencies, Part 2, NSRDS-NBS-11—In press Tables for the Rigid Asymmetric Rotor: Transformation Coefficient for Symmetric to Asymmetric Bases and Expectation Values of Pf and P*. NSRDS-NBS 12—In press Hydrogenation of Ethylene on Metallic Catalysts. NSRDS-NBS 13—In press *Send orders with remittance to: Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Remittances from foreign countries should include an additional one-fourth of the purchase price for postage. UNITED STATES DEPARTMENT OF COMMERCE Alexander B. Trowbridge, Secretary NATIONAL BUREAU OF STANDARDS A. V. Astin, Director X-Ray Wavelengths and X-Ray Atomic Energy Levels J. A. Bearden The Johns Hopkins University Baltimore, Maryland Reprinted from Reviews of Modem Physics [ Vol. 31, No. 1, January 1967 ] NSRDS NSRDS-NBS 14 National Standard Reference Data Series- National Bureau of Standards 14 (Category 3—Atomic and Molecular Properties) Issued September 25, 1967 For sole by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - Price 40 cents Foreword The National Standard Reference Data System is a government-wide effort to give to the technical community of the United States optimum access to the quantitative data of physical science, critically evaluated and compiled for convenience. This program was established in 1963 by the President’s Office of Science and Technology, acting upon the recommendation of the Federal Council for Science and Technology. The National Bureau of Standards has been as- signed responsibility for administering the effort. The general objective of the System is to coordinate and integrate existing data evaluation and compilation activities into a systematic, com- prehensive program, supplementing and expanding technical coverage when necessary, establish- ing and maintaining standards for the output of the participating groups, and providing mecha- nisms for the dissemination of the output as required. The NSRDS is conducted as a decentralized operation of nation-wide scope with central co- ordination by NBS. It comprises a complex of data centers and other activities, carried on in government agencies, academic institutions, and nongovernmental laboratories. The independent operational status of existing critical data projects is maintained and encouraged. Data centers that are components of the NSRDS produce compilations of critically evaluated data, critical re- views of the state of quantitative knowledge in specialized areas, and computations of useful functions derived from standard reference data. For operational purposes, NSRDS compilation activities are organized into seven categories as listed beiow. The data publications of the NSRDS, which may consist of monographs, loose- leaf sheets, computer tapes, or any other useful product, will be classified as belonging to one or another of these categories. An additional “General” category of NSRDS publications will include reports on detailed classification schemes, lists of compilations considered to be Standard Reference Data, status reports, and similar material. Thus, NSRDS publications will appear in the following eight categories: Category T itle 1 General 2 Nuclear Properties 3 Atomic and Molecular Properties 4 Solid State Properties 5 Thermodynamic and Transport Properties 6 Chemical Kinetics 7 Colloid and Surface Properties 8 Mechanical Properties of Materials The Present compilation is in category 3 of the above list. It constitutes the 14th publication in the new NBS series known as the National Standard Reference Data Series. A. V. Astin, Director. in I r " : . Preface The publication philosophy of the National Standard Reference Data System recog- nizes that data compilations will be most useful if all available channels of publishing and disseminating the information are employed. Selection of a specific channel—Govern- ment Printing Office, a scientific journal, or a commercial publishing house—is deter- mined by the circumstances for the individual document concerned. The goal is to reach all of the appropriate audience most readily at minimum expense. The two compilations which follow were first published in “Reviews of Modern Physics.” The authors and the editors felt that journal would reach the intended readers, and the Office of Standard Reference Data agreed. However, all concerned underesti- mated the demand for reprints, and the supply was exhausted soon after publication. With the generous permission of the editors of “Reviews of Modern Physics,” and the approval of the authors, the Office of Standard Reference Data has undertaken to reprint the articles as a part of the National Standard Reference Data System—National Bureau of Standards series. V Contents Page Foreword III Preface v X-Ray Wavelengths J. A. Bearden 1 Reevaluation of X-Ray Atomic Energy Levels J. A. Bearden and A. F. Burr 49 VI X-Ray Wavelengths V J. A. BEARDEN The Johns Hopkins University, Baltimore, Maryland 4 Inconsistencies in accepted values (in x units) of x-ray reference lines have recently been demonstrated, although all are supposedly based on “good” calcite crystals. Factors supporting the selection of the W Ka\ line as the X-Ray Wave- length Standard are critically discussed. A review is given of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis. Its value is X W Kai = (0.2090100±5 ppm) A. This may be used to define a new unit, denoted by *, such that the W Kai wavelength is exactly 0.2090100 A*; hence 1 A* = lA±5 ppm. The wavelengths of the Ag Kai, Mo Ken, Cu Kai, and the Cr Ken have been established as secondary standards with probable A*error of approximately one part per million. Sixty-one additional x-ray lines have been used as reference values in a com- prehensive review and reevaluation of more than 2700 emission and absorption wavelengths. The recommended wavelength values are listed in A * units together with probable errors; corresponding energies are given in keV. A second table lists the wavelengths in numerical order, and likewise includes their energies in keV. CONTENTS lengths. The best known reviews are those of Siegbahn,3 Cauchois and Hulubei, and Sandstrom.6 Introduction 1 very serious discrepancy A Primary X-Ray Wavelength Standard 2 A exists in each of these Inadequacy of the Calcite xu Standard 2 tabulations (and all others) : The shorter and longer Considerations in the Selection of a Wavelength Standard. 2 wavelengths are not on the same relative energy scale. Wavelength Defined by Peak Intensity of Line 2 Selection of a Wavelength Region 3 In general wavelengths less than 1.0 A are consistent Width and Symmetry Effects 3 with a Mo Ka\= 707.831 xu scale, and those of longer Source Requirements 3 wavelength with a Cu Kai = 1537.400 xu scale. Recent Crystal Considerations 4 6 The W Kai Wavelength Standard 5 higher precision measurements of the Mo Aai and The W Kai Wavelength 5 Cu Kai wavelengths, with carefully selected diffraction Secondary Standards 5 crystals of various materials shows that the above Additional Reference Standards 6 X-Ray Wavelength Conversion Factor A(\ e/X,) 6 values are in disagreement by almost 20 parts per Recomputation of X-Ray Wavelengths 7 million (ppm) or approximately twenty times the Literature Data 7 previous estimates7 of the probable error. If Conventions 8 we assume Errors 8 the xu defined by the first-order grating constant Wavelength Tables V and VI 8 of calcite (di = 3029.04 xu) the new measurements are Acknowledgments 47 consistent with a Cu Kai value of 1537.400 xu. The INTRODUCTION cause of the apparent errors in the Mo Kai and other short wavelengths is still unknown. The higher energy emission and absorption x-ray In addition to the above discrepancy in the relative wavelengths provide energy reference standards for values of the wavelengths, the xu,8 which was intended nuclear /3- and 7-ray spectroscopy. Crystallographic to be 10~3 A, differs from this absolute scale by more dimensions are usually measured with the Mo Kai, than 200 ppm. Early measurements of x-ray wave- Cu Ka\, and other longer x-ray wavelengths. Accurate lengths were made with NaCl crystals whose grating relative values of the occupied atomic energy levels constant d — 2.814 A was calculated9 from the crystal have been calculated 1 by the use of all the emission geometry, molecular weight, density, and Avogadro’s x-ray wavelengths of an element, and the absolute number. The latter was evaluated from the Faraday scale can be derived from the wavelength of the and the oil-drop value of the electronic charge which absorption edge, or more accurately from x-ray emis- was in error by more than 600 ppm. Siegbahn8 noted sion wavelengths, and electron energy measurements the superiority of calcite crystals to NaCl for spectro- from photoionization experiments.2 3 Wavelength values for more than twenty-seven M.