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by: Humberto Bosco DVM


Marketplace > Texas A&M University > Geology > GEOL 689 > SPTP RADIOGENIC ISOTOPE GEOCH
Humberto Bosco DVM
Texas A&M
GPA 3.99

Renald Guillemette

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About this Document

Renald Guillemette
Class Notes
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This 12 page Class Notes was uploaded by Humberto Bosco DVM on Wednesday October 21, 2015. The Class Notes belongs to GEOL 689 at Texas A&M University taught by Renald Guillemette in Fall. Since its upload, it has received 10 views. For similar materials see /class/225973/geol-689-texas-a-m-university in Geology at Texas A&M University.




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Date Created: 10/21/15
Quantitative Analysis W D S Basic relationship between concentration and Xny counts CA IA 2 kA cA cone of element A I A intensity of Xitay from element A k A proportionality factor not followed exactly except in simplest circumstances with very thin films Sources of error in quantitative analysis A operator errors B sampling and sample preparation errors C instrumenml errors D statistical errors see Williams app B pp 354359 E intetelement matrix errors a Incident b electron beam Monte Carlo Model of IOOe39 paths Emflml la39Imns e lltl Auger 402 Secondary SE 500A Backseattcred ESE EUNHEMID L Characterls 10 Continuous Fluorescent QIILchmducIs t t Cathodolumnesccnce Approving Shula lIml Absorbed Electrons L0 14m pz gt J p2 v y lt y gt Figure 99 The forms of the depth and lateral generated intensity functions Qz and y The vertical dimension in this gure is that of depth beneath the sample surface expressed as mass thickness 92 and the horizontal dimension is lateral distance from the electron beam axis expressed in arbitrary units y These functions indicate that most Xrays are generated at relatively shallow depths within the excitation volume and relatively close to the beam axis this is the region in which electron energies have not been greatly attenuated by ionization or electron scattering 3900 LCu K Figure 6 13 Comparison of Xray production regions from specimens with densities of 3 gcm3 left and 10 gcm3 right at a beam energy of 20 keV The xray spatial resolution Lx is found by projecting the maximum diameter of the xray distribution to the surface of the specimen Figure 93 Simpli ed schematic representation of electron energy loss and sample attenuation of generated X ray intensities in electron microprobe analysis In nite depth corresponding to L in Fig 972 is the depth at which electron energy is reduced to Em the critical excitation potential of the analytical radiationt However electrons may still have suf cient energy below this depth to excite continuous and lowerenergy characteristic radiation Approaches to matrix correction a Simply recognize and tolerate errors 7 only good for relative applications and not very good even then b Simplify theory to yield less complicated correction procedures appropriate to applications in which the simpli cations are justified c Experimental observations can be used to derive empirical correction coef cients that can be used Within speci c systems with theoretically limited but practically useful compositional ranges Simplified Theory Approach 1 Electrons lose energy by a series ofmultiple collisions generating characteristic X7 rays as long as a electron remains Within the sample b E ofelectron gt critical excitation energy ofthe X7rays used in the analysis 2 X7rays then interact with matter in the sample along the exit path Some processes attenuate X rays others enhance 3 Major processes a electron paths and the question ofelectron energy transfer to X7ray generation absorption ofX7rays Within the sample c uorescent enhancement within the sample a is strongly dependent on atomic number and is therefore usually called quotZquot correction although quotgeneration factorquot might be more appropriate 7 quotZquot correction is usually broken down into 2 components 7 generation of back7scattered electrons 7 stopping power tomzationpenetration 7 Deals with ef ciency ofX7ray production depends on 1 ionization cross7section ofsatnple for K L etc electrons 2 ofatonls encountered density 3 way in which energy is lost during deceleration 4 potential ionization energy loss due to BSE s 7 Penetration and BSE effects tend to partially compensate for each other meaning that the Z correction is usually not the most signi cant of the 3 quotAquot correction deals with absorption ofX rays Within sample depends on depth distribution ofX rays estimate oftotal composition of sample values ofthe mass absorption coef cients 7 Major problem in ZAF corrections 7 Inass absorption corrections are not vety well known especially for long wavelength Xrays 7Considering the problem oerray absorption actually stroneg depends 011 ottr ability to understand depth dependence of eray generation ABLE 73 Mun absorption u llit it39llls milg ujicr Heinritli Emitter wavelength in A Absorber A1 Si Ti V Cr Mn Fe Co Ni Cu 8337 7126 2748 2504 2291 2103 1937 1790 1659 1542 13 Al 3257 34932 2470 1908 1490 1174 934 750 607 496 14 Si 5034 3279 3043 2352 1838 1450 1155 928 752 614 22 Ti 22880 14906 110 6 2558 5970 4725 3775 3044 2473 2026 23 V 26214 17078 1267 983 771 5311 4243 3421 2780 2277 24 CI 30005 19548 145 U 112 5 88 2 w 9 4713 3823 3107 2544 25 Mn 34156 22253 1651 1281 1005 795 635 4225 3436 2816 26 Fe 38406 25021 1856 1440 1130 894 714 576 3796 3111 27 Co 43308 28216 2093 162 1 1274 100 1 806 649 528 3412 28 Ni 48375 31516 2338 1811 1423 1126 90 0 725 589 483 29 Cu 5 3768 35030 2598 2016 1581 1252 1001 806 655 537 The table gives data for the absorption 01K radiation from some 541th elements The complete table covers the range NaMo K radiation Ga U L radiation and Yb U M rudialion quotFquot correction deals with 2 types of uorescence 7 generated by characteristic X7i39ays generated by continuous quotwhitequot Xra s 7 former is generally much more important Fluorescence depends on 1 operating voltage 2 concentration ofelement 3 absorption 4 excited X7rays both inside and outside oftlie primary excitation volume 5 take7olfang e 6 atomic number 7 Secondary vs tertiary 7 K7K vs K7L and L7 fluorescence 7 Phase boundary effects not corrected by most software In general analyte concentration CA is given by cA RAZAF rr2 Equation 112 may be expanded as follows CA 1A A Sx flit 391 10351 Mt quotx 5A 111 l E Ii1 loomla 3 where the three bracketed terms are the atomic number absorption and uorescence corrections respectively and are expanded below n the atomic number correction r is the electronbackseatter coef cient and is the ratio of ionization produced to that which would be produced in the absence of backseatter and s is the electron stopping power 3 ilog ll7 ll4 where Z and A are atomic number and weight respectively V and V are electron acceleration potential and excitation potential respectively and V is the mean ionization potential In the absorption correction 1 f of chiquot is the fraction of the generated analyteline photons that are actually emitted l h w I acUml hll 10 where x is the attenuation ofthe emergent analyteline x rays his an electron penetration term and a is the effective Lenard electron absorption coef cient as modi ed by Heinrich 1 5 It 049 CSC W I 16 hi l2AZ 1 L7 7 45x l05VH7 Vil quot 118 where 019quotA is the massabsorption coef cient ofelement ifor the analyte line AA w is the xray emergence angle and A Z V and V are de ned above In the uorescence correction the enhancement of the analyte line A by spectral lines of matrix elements j is given by the ratio of analyteline intensities excited by elements j I and directly by the electron beam In summed for all matrix lines that can signi cantly enhance AA Ii n 1 AA UV 1 7 rte 05P Ci J l 2 1A A 1 A w A UA 1 fl9hr x g v 0 j A 9 in which zA VVA and U VVj 1110 u Qt9 A csc w111ex1 llll v aFQXA 1 1J2 Simplified Theot39vApp139oach l Electrons lose energy by a series of multiple collisions generating characteristic XA rays as long as a electron remains Within the sample b E ofelectron gt critical excitation energy of the Xirays used in the analysis 2 Xerays then interact with matter in the sample along the exit path Some processes attenuate X rays others enhance 3 Major processes a electron paths and the question of electron energy transfer to Xiray generation b absorption ofX7rays Within the sample c uorescent enhancement Within the sample a is strongly dependent on atomic number and is therefore usually called quotZquot correction although quotgeneratlon facto1quot391n1ght be more appropnate HICROPROBE ANALYSIS 1 SAN CARLOS AS 1111K 1 HT 1 HEIGHT ATOHIC INTENSITIES BACKSROUNDS ELEMENT OXIDE PERCENT PERCENT KRAHO UNKN STD ONKN 6 FE KA 77312 60096 22361 101369 5781 5702 157 240 S 1111 410169 191731 141859 099702 13768 13809 24 240 HO KA 507702 306200 261721 100193 75702 75556 240 240 O I 441972 574059 TOTAL 995182 6 ITERATIONS t DETERMINED BY D1FFERENEE CORRECTIONS ELENENT BKSCATR IONPEN ABSORP FLUORES TOTAL FE KA 09319 12512 09981 10000 11637 51 1111 09819 10378 14193 09999 14461 116 KA 09962 10197 14204 09973 14390 Intro to Image Analysis Image Processing for Microprobe Analyses of Geological and Metallurgical Samples Introduction Scannin Electron Microscope amp Electron Microprobe Similarities and Differences Sources of Video Signals condary Electrons SE Backscattered Electrons BSE XRay Detectors nergy Dispersive Spectrometry EDS Wavelength Dispersive Spectrometry WDS Digital vs Analog Images Basic Terminology Resolution and y 2 bit depth Gra scale vs Color Acquiring Digital Images on the Electron Microprobe Most useful sources for digital image analysis E and XRay ma s Advantages of WDS over EDS maps Better Peak to Background ratio Better Spectral Resolution Disadvantages Higher Beam Current Required Lower total count rates Simultaneous element acquisition limited to of spectrometers Combining two or more signal sources into a single composite image 2 pproaches 1 Combining 3 channels of grayscale information into a single 24 bit image or recalculated 8 bit ima e 2 Combining up to 7 thresholded binary 1 bit images into a single grayscale or falsecolored 8 bit image Advantages of approac Quick and easy minimal processing and decisionmaking required Shows relatively subtle variations in composition Disadvantages of approach 1 May be 39 ficult to subsequently quantify resulting image additive results not numerically obvious Advantages of approach 2 Up to 7 vs 3 combined images Thresholded images are usually easier to subsequently quantify Disadvantages of approac More work and DecisionMaking Number of possible additive permutations can become daunting Use of Image Analysis software to quantify composite images Modal Analysis Shape and Size Analysis Preferred Orientation Analysis 224 gt 24 bit gt 16777215 colors 215 gt16 bit 32768 colors 28 gt8 bit 256 colors 27 gt 7 bit gt 128 colors 26 gt 6 bit 5bit gt 64 colors 25 32 colors 24 4 bit 23 I 3 blt gt 8 colors 4 colors 16 colors Ij 1blt 2 colors Exam Ie Conversion ofS bit XRa Intensit Ma s to Uni ue value binar ma 5 Grayscale 8 bit Binaiy 1 bit Si pixels 16 39 39 I r Al pixels 32 Fe pixels 128 Grayscale 8 bit Binary 1 bit Si Quartz Gray Si Al Plag Feldspar Blue Si A1 K KFeldspar Green Fe Fe FeTi oxide Yellow Fe Si Al Fe Silicates Red


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