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The Holistic Analysis of Gamma-Ray Spectra in Instrumental Neutron Activation Analysis 0'

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The Holistic Analysis of Gamma-Ray Spectra in Instrumental Neutron Activation Analysis 0' INIS-mf—15160 The Holistic Analysis of Gamma-ray Spectra in Instrumental Neutron Activation Analysis 0' Menno Blaauw n f '1 \9 KS001969803 I: FI *DE00835510X* DE00835510X The Holistic Analysis of Gamma-ray Spectra in Instrumental Neutron Activation Analysis Menno Blaauw i Interfacultair Reactor Instituut van de Technische Universiteit Delft 1993 )L 2 7 f|g t f CIP-DATA KONINKLIJKE BIBLIOTHEEK, DEN HAAG Blaauw, Menno The holistic analysis of gamma-ray specira in instrumental neutron activation analysis / Menno Blaauw. - Delft: Interfacultair Reactor Instituut, Delft University of Technology. -111. Thesis Technische Universiteit Delft. - With ref. - With summary in Dutch. ISBN 90-73861-16-0 NUGI 813 Subject Headings: Instrumental neutron activation analysis / gamma-ray spectrometry The Holistic Analysis of Gamma-ray Spectra in Instrumental Neutron Activation Analysis (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus, prof. ir. K.F. Wakker, in het openbaar te verdedigen ten overstaan van een commissie aangewezen door het College van Dekanen op maandag 15 november 1993 te 16.00 uur door Menno Biaauw doctorandus in de natuurkunde geboren te Utrecht in Dit proefschrift is goedgekeurd door de promotoren: prof.dr.ir. M. de Bruin en prof.dr.ir. W. Lourens IV Het in dit proefschrift beschreven onderzoek is uitgevoerd bij de groep Fysisch-mathematische Radioanalyse van de afdeling Radiochemie van het Interfacultair Reactor Instituut van de Technische Universiteit Delft, Mekelweg 15, 2629 JB Delft. VI Dirk Gently: "I believe, as you know, Mrs Sauskind, in the fundamental interconnectedness of all things. Furthermore, I have plotted and triangulated the vectors of the inter- connectedness of all things and traced them to a beach in Bermuda which it is therefore necessary for me to visit from time to time in the course of my investigations. I wish it were not the case, since, sadly, 1 am allergic to both the sun and rum punches, but then we all have our crosses to bear, do we not, Mrs Sauskind?" (Douglas Adams, Dirk Gently's holistic detective agency, Pan Books, 1987) Opgedragen aan Corbie en ter nagedachtenis aan haar vader Wim vu vin Contents Chapter 1 General Introduction 1 1.1. Introduction to Neutron Activation Analysis 1 1.2. Theoretical introduction to 1NAA 1 1.2.1. Activation 1 1.2.2. Decay 2 1.2.3. Measurement 4 1.2.4. Analysis of 1NAA gamma-ray spectra 4 1.3. Historical development of NAA 5 1.4. Developments at the lntcrfaculty Reactor Institute 6 1.5. Scope of the present study 7 1.6. Aims of the present study 8 Part I: Reduction of gamma-ray spectra 9 Part II: Standardization 9 Part III: Interpretation of gamma-ray spectra 10 1.7. References 11 Chapter 2 Introduction to Spectrum Reduction 14 2.1. Introduction to gamma-ray spcclromctry 14 2.2. Description of the problem 16 2.3. Mathematical representation of the problem 17 2.4. Methods of solving the problem 18 2.5. References 19 Chapter 3 Statistical Properties of the Peak Search Algorithm as Related to Curric's Detection Limits 20 3.1. Introduction 20 3.2. Currently applied filters 21 3.2.1. Cross correlation filters 21 3.2.2. The Savitzky-Golay filter 22 3.2.3. The Mariscotti filter 24 3.2.4. Continuum subtraction method 24 3.2.5. The Routli-Prussin filler 25 3.2.6. The Wiener filter 26 3.2.7. Comparison of filters 27 3.3. Experimental 28 3.4. Results 31 3.4.1. The values of /J 31 3.4.2. The values of o 33 3.4.3. The probability of making a type 1 error 35 3.4.4. Differential non-linearity 35 3.5. Discussion 36 3.6. Conclusions 37 3.7. References 37 Chapter 4 The Fitting of Photopcaks 39 4.1. Introduction 39 4.2. Peak shape 39 4.3. Overlapping peaks and multiplcts 41 4.4. An overview of the procedure 42 4.5. Shape calibration 43 ix 4.5.1. Estimation of peak position 44 4.5.2. Estimation of peak width 44 4.5.3. Estimation of tail parameters 44 4.5.4. Estimation of peak area 44 4.5.5. Estimation of Compton step 45 4.5.6. Estimation of continuum parameters 45 4.5.7. Determination of region of spectrum to fit 45 4.5.8. Selection of peaks to use 45 4.5.9. The filling procedure 45 4.5.10. Shape calibration curves 46 4.5.11. User interaction 47 4.6. Energy calibration 47 4.7. Reduction of an unknown spectrum 47 4.7.1. Peak search 47 4.7.2. Estimation of parameters 47 4.7.3. The fitting procedure 47 4.7.4. Total area computation 48 4.7.5. The "range" concept 48 4.7.6. Recognition of problematic fits 48 4.7.7. User interaction 49 4.8. Conversion lo energy, correction for dead time, pile-up and background 50 4.9. References 51 Chapter 5 Introduction to Standardization 54 5.1. Methods of standardization 54 5.2. Single comparator methods 56 5.3. References 58 Chapter 6 An Alternative Convenlion Describing the (n,7)-Rcaction Rale Suited for Use in the k0-Mcthod of INA59 6.1. Introduction 59 6.1.1. Theory 61 6.1.2. The adapted Hylgdahl convenlion 61 6.1.3. The alternative convenlion 63 6.1.4. Suitability of the alternative convention for use in the kj-method 65 6.2. Discussion 65 6.2.1. Mathematical simplicity and applicability 65 6.2.2. The role of Cd 66 6.3. Conclusions 67 6.4. References 67 Chapter 7 Introduction of the k,-Conccpt for the Interpretation of "Artificial" Peaks in ko-Based 1NAA 69 7.1. Introduction 69 7.2. The inability of the k0-method to deal with "artificial" peaks 69 7.3. "Artificial" peaks of the first kind: Definition of the k,-constant 70 7.4. "Artificial" peaks of the second kind: Extension of the description of detector efficiency ... 71 7.5. The k,-method in practice 72 7.5.1. Determination of the k,-constant 72 7.5.2. The use of the ^-constant 73 7.6. Discussion 73 7.7. Conclusions 76 7.8. References 76 x \ Chapter 8 Comparison of the k„- awl the k^-catalogucs 77 8.1. Introduction 77 3.2. Comparison of catalogues 77 8.2.1. Old-style IRI catalogues for coaxial detectors 77 8.2.2. Old-style IRI catalogues for well-type detectors 78 8.2.3. Conversion to k,-catalogues 79 8.2.4. Comparison of k-^- and k„-catalogucs 8U 8.3. Results 82 8.4 Conclusions 83 8.5. References 83 Chapter 9 The Use of Sources Emitting Coincident Gamma-rays for Determination of Absolute Efficiency Curves of Highly Efficient Gc Detectors 84 9.1. Introduction 84 9.2. Theory 85 9.2.1. Coincidence summing 85 9.2.2. Determination of the efficiency curves and source activity from a measured spectrum 88 9.3. Experimental 90 9.3.1. Source preparation 90 9.3.2. Measurement and spectrum analysis 90 9.3.3 TV., oroccssing 91 9.4. Re .'»•.. ru discussion 92 9.4.1. i?l''j. n (ration of the fca, i;(lity of the method 92 9.4.2. Sour>.<- .rf;»rfly sensitivity of the three detectors 93 9.5. Conclusions 97 9.6. References 98 Chapter 10 A Versatile Computer Algorithm for Linear First-order Equations Describing Comparlmcntal Models with Backward Branching 100 10.1. Introduction 100 10.2. Derivation of a general formula for linear structures 101 10.3. Implementation of the general formula 105 10.4. Decomposition of complex structures of interrelated compartments 106 10.5. Two examples 107 10.5.1. Dynamic equilibrium 107 10.5.2. Sccundary activation in Neutron Activation Analysis 107 10.6. References 108 Chapter 11 Interpretation Techniques 112 11.1. Introduction 112 11.2. References 114 Chapter 12 The Holistic Interpretation of Reduced Gamma-ray Spectra 115 12.1. Introduction 115 12.2. Computation of basic spectra 116 12.2.1. Computation of basic spectra of the elements for fluxmonitors 117 12.2.2. Computation of basic spectra of the elements for samples 117 12.3. Assignment of peaks 117 12.4. Determination of maximal amounts 118 12.5. Elimination of insignificant contributions 118 XI 12.6. Insertion of missing peaks in the measured spectra 119 12.7. Extraction of independent subsets of equations 119 12.8. Identification of undistinguishablc entities 119 12.9. Solving or fitting the subsets of equations 120 12.10. Sources of error and their propagation 121 12.10.1. The effective k,-constant 121 12.10.2. f, a, Qo\ and E, 122 12.10.3. Half lives 122 12.10.4. The P value 122 12.10.5. Neutron flux 123 12.10.6. Observed peak area 123 12.11. References 124 Chapter 13 Experimental Comparison of Two lnlcrprelation Techniques 125 13.1. Introduction 125 13.2. Experimental 125 13.2.1. Sample preparation 125 13.2.2. Irradiation and measurement 125 13.2.3. Spectrum analysis 126 13.3. Results 127 13.3.1. Citrus Leaves (NBS-1572) 127 13.3.2. Buffalo River Sediment (NBS-2704) 127 13.3.3. Pig Kidney (BCR-186) 127 13.3.4. Coal Fly Ash (NBS-1633a) 128 13.4. Discussion 129 13.5. Conclusions 130 13.6. References 131 Chapter 14 Multiple! Dcconvolution as a Cause of Unstable Results in Gamma-ray Spcctromelry for INAA .
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