TECHNICAL REPORTS SERIES No. 115 Radioisotope X-Ray Fluorescence Spectrometry INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA,1970 RADIOISOTOPE X-RAY FLUORESCENCE SPECTROMETRY The following States jre Members of the International Atomic Energy Agency: AFGHANISTAN GREECE NORWAY ALBANIA GUATEMALA PAKISTAN ALGERIA HAITI PANAMA ARGENTINA HOLY SEE PARAGUAY AUSTRALIA HUNGARY PERU AUSTRIA ICELAND PHILIPPINES BELGIUM INDIA POLAND BOLIVIA INDONESIA PORTUGAL BRAZIL IRAN ROMANIA BULGARIA IRAQ SAUDI ARABIA BURMA IRELAND SENEGAL BYELORUSSIAN SOVIET ISRAEL SIERRA LEONE SOCIALIST REPUBLIC ITALY SINGAPORE CAMBODIA IVORY COAST SOUTH AFRICA CAMEROON JAMAICA SPAIN CANADA JAPAN SUDAN CEYLON JORDAN SWEDEN CHILE KENYA SWITZERLAND CHINA KOREA, REPUBLIC OF SYRIAN ARAB REPUBLIC COLOMBIA KUWAIT THAILAND CONGO, DEMOCRATIC LEBANON TUNISIA REPUBLIC OF LIBERIA TURKEY COSTA RICA LIBYAN ARAB REPUBUC UGANDA CUBA LIECHTENSTEIN UKRAINIAN SOVIET SOCIALIST CYPRUS LUXEMBOURG REPUBLIC CZECHOSLOVAK SOCIALIST MADAGASCAR UNION OF SOVIET SOCIALIST REPUBLIC MALAYSIA REPUBLICS DENMARK MALI UNITED ARAB REPUBLIC DOMINICAN REPUBLIC MEXICO UNITED KINGDOM OF GREAT ECUADOR MONACO BRITAIN AND NORTHERN EL SALVADOR MOROCCO IRELAND ETHIOPIA NETHERLANDS UNITED STATES OF AMERICA FINLAND NEW ZEALAND URUGUAY FRANCE NICARAGUA VENEZUELA GABON NIGER VIET-NAM GERMANY, FEDERAL REPUBLIC OF NIGERIA YUGOSLAVIA GHANA ZAMBIA The Agency's Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of the Agency are situated in Vienna. Its principal objective is "to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world". © IAEA, 1970 Permission to reproduce or translate the information contained in this publication may be obtained by writing to the International Atomic Energy Agency, Kamtner Ring 11, P.O. Box 590, A-1011 Vienna, Austria. Printed by the IAEA in Austria June 1970 TECHNICAL REPORTS SERIES No. 115 RADIOISOTOPE X-RAY FLUORESCENCE SPECTROMETRY REPORT OF A PANEL HELD IN VIENNA, 13 - 17 MAY 1968 INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1970 RADIOISOTOPE X-RAY FLUORESCENCE-SPECTROMETRY IAEA, VIENNA, 1970 STI/DOC/10/115 FOREWORD Radioisotope X-ray fluorescence is one of the more recent techniques developed as a result of the general availability of sealed radioisotope sources. It is mainly used for non-destructive elemental analysis and for the measure- ment of coating thickness. In both these applications it has become comple- mentary to, and competitive with, several older-established methods. A great variety of portable equipment for the analysis of alloys, both in industrial plant laboratories and in the field, now uses radioisotope X-ray fluorescence techniques as a basic element in its design. This equipment is in wide use in geophysical prospecting and in mine development and control. Also important in mining is the development of borehole probes for use in percussion-drilled holes; this is an attractive alternative to the analysis of drill cores. On-line equipment incorporating these techniques has been developed for use in mineral processing plants, especially for analysis of lead, zinc, tin, copper, iron, calcium and silicon. Although industry was slow to intro- duce this on-line application, several commercial installations are now reported to be in operation. For on-line measurement in particular, the combination of radioisotope X-ray fluorescence with neutron activation analysis (using radioisotope neutron sources) is now being developed. This will be especially useful where several elements have to be analysed simultaneously. Commercial equipment, designed for use in computer-control systems, is now available for regulating the thickness of coatings in the tinning and galvanizing processes. An important development is the work on low-Z analysis by alpha excitation. This method of analysis can now be seriously considered for industrial application, especially since an intrinsically safe alpha source, 242Cm, has recently become available commercially. Also important in ex- tending the range of applications is the development of solid-state detectors, particularly the Si(Li) type, with which inter-element effects can be reduced and limits of detection can be lowered; a main reason for the improvement here is that balanced X-ray filters are not required. The two problems limiting higher accuracy are those of inter-element effects — already largely solved — and of particle-size effects. Many experts are confident that present work aimed at overcoming particle-size effects will be successful. Although development work is proceeding in many directions, there is a wide range of possible uses that have as yet been barely explored. The Panel whose findings are reported here met in Vienna on 13—17 May 1968. Its task was to review current techniques and applications, to comment on the factors that limit performance, and to consider promising lines of development and extensions of present usage. The report is based on Panel discussions and on written contributions from each Panel Member, as well as on a paper by B. Dziunikowski, Institute of Radioisotope Techniques, Academy of Mining and Metallurgy, Cracow, Poland. The International Atomic Energy Agency is greatly indebted to C. G. Clayton, Chairman of the Panel, for compiling and editing the final text of the report and ensuring that the information is up to date. CONTENTS A. GENERAL CONSIDERATIONS . 1 A.l. Comparison between radioisotope X-ray fluorescence and other analytical techniques 1 A.1.1. General comparisons 1 A. 2. Comparison between radioisotope and conventional X-ray fluorescence analysis 4 A. 2.1. Relative performance 4 A.3. Comparison between primary and secondary alpha, beta, gamma and X-ray excitation 6 A.3.1. Principal characteristics of the different methods of excitation 6 A.3.2. Choice of source 9 A. 3.3. Comparison of the available excitation sources 15 A.3.4. A comment on proton excitation 16 A.4. Present status of the theory of radioisotope X-ray fluorescence 16 B. INSTRUMENTATION AND TECHNIQUES 19 B.l. Components of radioisotope X-ray fluorescent analysers 19 B.l.l. Radioactive sources 19 B.l.2. Detectors , 25 B.1.3. Electronic instrumentation 28 B.l.4. Windows 28 B.1.5. X-ray filters for energy selection 29 B.l.6. Cooling systems 30 B.l.7. Multi-element computers 31 B.2. Analytical Instruments and systems 32 B.2.1. Commercially available systems 32 B.2.2. Other systems in use or under development 40 B.3. Techniques for minimizing interference 41 B.3.1. Matrix effects 41 В. 3.2. Heterogeneity effects 42 B.4. Calibration 44 С. APPLICATIONS 45 C.l. Metalliferous mineral exploration and development 45 C.l.l. Unprepared rock surfaces 45 C.l.2. Drill cores 46 C.1.3. Boreholes 47 C.l.4. Particulate samples 47 C.2. On-stream process control 50 C.2.1. Introduction 50 C.2.2. Analysis of slurries 51 C.2.3. Analysis of crushed materials 63 C.2.4. Analysis of solutions 70 C.3. Alloy analysis 70 C.4. Coating thickness measurement 71 C.4.1. Introduction 71 C.4.2. X-ray fluorescence methods of measuring coating thickness 71 C.4.3. Applications 71 C.4.4. Tin coating gauges 71 C.4.5. Zinc coating gauges 77 C.5. Miscellaneous applications 78 C.5.1. Medical 78 C.5.2. Other applications 79 C.6. Health and safety considerations 79 C.6.1. External hazards 79 C.6.2. Internal hazards 80 D. PROSPECTS AND REQUIREMENTS 81 E. RECOMMENDATIONS TO THE AGENCY 83 REFERENCES 85 APPENDIX I — Manufacturers' specification forms 89 APPENDIX II — Classification of preferred terms and definitions relating to radioisotope X-ray fluorescence analysis 99 LIST OF PARTICIPANTS AND SECRETARIAT 101 A. GENERAL CONSIDERATIONS A. 1. COMPARISON BETWEEN RADIOISOTOPE X-RAY FLUORESCENCE AND OTHER ANALYTICAL TECHNIQUES Radioisotope X-ray fluorescence analysis is one of a number of tech- niques now available to determine the concentration of elements in different materials. Its suitability for any application depends on a variety of factors, such as the environment in which the analysis is to be carried out and the limits of detection required. In the present comparison, radioisotope X-ray fluorescence is first examined in a general manner and then compared specifically with conven- tional X-ray fluorescence analysis. A. 1.1. General comparisons (a) Analyses in the laboratory , A general comparison is difficult to make because of the many factors which have to be taken into account, but an attempt has been made to summarize the present situation in Table I. The different analytical techniques have been assigned a figure of merit, i.e. 1, 2, 3, 4 or 5 (1 indicating highest performance and 5 lowest performance) for the particular characteristics defined below. (i) Selectivity This is the ability of the technique to ensure that the signal being measured originates from the element being determined. (ii) Limit of detection This applies to the sample being examined but does not .take into account concentration or dilution factors. (iii) Accuracy This refers to the degree of correctness with which a method of measurement yields the true value of the quantity being measured. (iv) Equipment cost . This is the cost of all the equipment required to complete an analysis. 1 TABLE I. COMPARISON BETWEEN THE LABORATORY APPLICATION OF RADIOISOTOPE X-RAY FLUORESCENCE AND THAT OF OTHER ANALYTICAL TECHNIQUES Limit of Equipment Laboratory Technique Selectivity Accuracy detection cost cost Atomic absorption 1 1 3 2 2 Atomic fluorescence 1 1 3 2 2 Polarography 4 2 3 2 2 Colorimetric 4 2 3 1 1 Fast neutron 3 4 2 4 4 Radioisotope X.R.F. 3 4 2 2 1 Tube X.R.F. 2 3 1 4 3 Direct reader 2 2 1 3 3 Analytical time Operator time and grade Technique Massive Massive Powders Liquids solids solids Powders Liquids Atomic absorption 4 3 1 3 3 1 Atomic fluorescence 4 3 1 3 3 1 Polarography 5 4 3 4 4 3 Colorimetric 5 4 3 4 4 3 Fast neutron 2 1 2 2 1 2 Radioisotope X.R.F.