THE k 0 -STANDARDIZATION METHOD AND ITS MULTIFACETNESS: AN EMINENT TOOL TO MASTER PGAA/NAA

Transcription

1 THE k 0 -STANDARDIZATION METHOD AND ITS MULTIFACETNESS: AN EMINENT TOOL TO MASTER PGAA/NAA ================================================ Frans DE CORTE ================================================ (ex) University of Gent-Belgium and Scientific Research Foundation-Flanders fransmans@skynet.be

2 k 0 -NAA (mid-1970s) ready-to-use suitable NAA/PGAAstandardization technique development implementation application need to study and understand its many inherently associated facets

3 BASIC EQUATION a analyte m - monitor Ultimate comparator 197 Au(n,γ) 198 Au kev

4 x nuclear data library recommended k 0 s

5 HØGDAHL CONVENTION, only for 1/v cross sections in the thermal neutron energy region reaction rate = subcadmium (up to E cd ) + epicadmium (from E cd ) [E Cd = 0.55 ev] f = ø s / ø e, where ø s contains an integration up to E Cd Q 0 = I 0 /σ 0, where I 0 contains an integration from E cd Important parameter R Cd = total/epicadmium reaction rate OTHER CONVENTIONS, including non-1/v cases - Westcott convention - Stoughton-Halperin convention - Extended/modified Høgdahl approximation More complex Requiring the knowledge of g(t n ) T n maxwellian neutron temperature

6 CORRECTING FOR THE CONTRIBUTION OF EPITHERMAL ACTIVATION The parameter α corrects the resonance integral (in Q 0 = I 0 /σ 0 ) for a non-1/e epithermal neutron flux distribution, represented by 1/E 1+α. This correction involves the knowledge of the parameter E r, the effective resonance energy f and α have to be experimentally determined (various methods possible) Q 0 and E r are nuclear constants (measurement/calculation nuclear data library)

7 G th - CORRECTION FACTOR FOR THERMAL NEUTRON SELF-SHIELDING G e - CORRECTION FACTOR FOR EPITHERMAL NEUTRON SELF-SHIELDING to be calculated from sample shape, volume, density, composition, cross sections

8 F Cd,m F Cd,a In case of ENAA ( f = 0 ) - Q 0, α and E r more critical - introduction of F Cd Cd transmission factor for epithermal neutrons also in all cases where use is made of a Cd-cover, e.g. k 0 determination via Cd subtraction method; Q 0 and α determination via R Cd and Cd-covered methods

9 N p measured peak area, to be correctd for: TRUE-COINCIDENCE EFFECTS (CASCADING γ-γ, γ X) the calculation of the coincidence correction factor COI requires the knowledge of the (simplified) decay scheme and its relevant parameters, of the full-energy peak detection effeciency ε p (coincidence summing) and/or the total detection efficiency (coincidence loss) ε t = ε p P T P/T IS THE PEAK-TO-TOTAL RATIO experimentally measurable, depending on photon energy, source-detector separation, ---

10 N P MEASURED PEAK AREA, to be corrected for: BURN-UP - of target/directly formed/daughter/granddaughther nuclide - significant for high cross sections, long t irr, high ø s - e.g. 197 Au*(n,γ) 198 Au**; F burn * = 0.98, F burn ** = 0.52 for t irr =14d and ø s = cm-2 s-1 PRIMARY REACTION INTERFERENCES - e.g. 116 Sn(n,γ) 117m Sn interfered by 117 Sn(n,n ) 117m Sn knowledge of fission neutron cross sections required 235 U FISSION INTERFERENCES - e.g. 139 La(n,γ) 140 La interfered by 235 U(n,f) 140 Ba 140 La introduction of experimental k 0,Au (fiss) factors

11 SDC S saturation factor = 1 e λt irr D decay factor = e λt d C counting factor = e λt m λt m MOFICATION REQUIRED in case of complex activation and/or decay t m g d gd, measured sometimes k 0 (m), k 0 (m), Q 0 (m), k 0 (g), etc required

12 SDC S saturation factor = 1 e λt irr D decay factor = e λt d C counting factor = e λt m λt m MOFICATION OF S REQUIRED In case of neutron flux variability during irradiation, including intermittent irradiation: * knowledge of flux variation required (reactor operation logbook ---) THIS IS ULTIMATE CONDITION OF APPLICABILITY OF k 0 -STANDARDIZATION!!!

13 FULL ENERGY PEAK DETECTION EFFICIENCY (including gamma attenuation) e.g. via SOLID ANGLE concept ε p,geo= ε p,ref Ω geo Ω ref where ref (reference) experimental for point sources at large source-detector distance geo (actual source-detector configuration) Ω = source detector F eff F att dω

14 FULL ENERGY PEAK DETECTION EFFICIENCY (including gamma attenuation) To be extended to low energies for measuring with an LEPD To be extended to high energies in PGAA

15 TRACEABILITY: Certified Al 0.1 % Au alloy (IRMM-530, IRMM-530R, ERM-EB530) UNCERTAINTY: taking into account all parameters and covariances QC/QA OF IMPLEMENTATION: SMELS

16 DEVELOPMENT AND USE OF DEDICATED SOFTWARE KAYZERO(-SOLCOI) : DSM, K0-WARE K0-IAEA PROGRAM HOME-TAILORED

17 CONCLUSION The items mentioned above amply demonstrate the multifacetness of the k 0 -method Hence its suitability for going to the bottom of (to master) NAA/PGAA

18 REFERENCE IS MADE TO THE PROCEEDINGS OF THE SIX FORMER INTERNATIONAL k 0 USERS WORKSHOPS GENT 1992 LJUBLJANA 1996 BRUGES 2001 FUNCHAL 2005 BELO HORIZONTE 2009 BUDAPEST YEARS AND TO THE PRESENTATIONS MADE IN THE PRESENT SEVENTH WORKSHOP MONTREAL 2017

19 * I AM GRATEFUL TO ALL MY STUDENTS, CO-WORKERS AND COLLEAGUES - ALLOVER THE WORLD FOR THEIR SIGNIFICANT CONTRIBUTIONS TO THE DEVELOPMENT OF k 0 -NAA/PGAA AND FOR KEEPING THE METHOD ALIVE AND KICKING * MY SPECIAL THOUGHTS GO TO ANDRÁS SIMONITS, MY BROTHER IN CRIME FROM THE FIRST HOUR