DIN 51003-2004 Total reflection x-ray fluorescence - Principles and definitions《全反射X-射线荧光 总则和定义》.pdf

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1、May 2004DEUTSCHE NORM Translation by DIN-Sprachendienst.In case of doubt, the German-language original should be consulted as the authoritative text.English price group 16No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth V

2、erlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 71.040.50!,y4v“9861783www.din.deDDIN 51003Total reflection X-ray fluorescence analysis (TXRF) Terminology and general principlesTotalreflexions-Rntgenfluoreszenz-Analyse (TXRF) Allgemeine Grundlag

3、en und Begriffewww.beuth.deDocument comprises 46 pagesDIN 51003:2004-05 2 Contents Page Foreword. 3 1 Scope . 4 2 Normative references. 4 3 General definitions . 4 4 Physical principles . 8 5 X-ray sources 12 6 Primary radiation modulation 14 7 Beam guidance . 15 8 Measurement of X-ray fluorescence

4、radiation in energy-dispersive spectrometers 15 9 Sample . 17 10 Recording and evaluation of the signal . 20 11 Traceability in TXRF . 24 12 Fields of application of TXRF 26 Annex A (normative) Additional information relating to 10.4.3 (absolute method) 37 Bibliography. 42 Alphabetical index . 43 DI

5、N 51003:2004-05 3 Foreword This standard has been prepared by Technical Committee Grundlagen der analytischen Atomspektroskopie of the Normenausschuss Materialprfung (Materials Testing Standards Committee). In recent years total reflection X-ray fluorescence analysis (TXRF) has become established as

6、 an independent technique for microanalysis, trace element analysis and surface analysis. The technique differs in many of its characteristics from classical X-ray fluorescence analysis (XRF or RFA) spectrometry. In its operation it has a number of features in common with other atomic spectroscopic

7、methods such as atomic absorption spectrometry (AAS) or inductively coupled plasma spectrometry techniques (ICP-OES and ICP-MS) in the field of trace element analysis, or with Auger electron spectroscopy (AES), Rutherford backscattering spectroscopy (RBS) or secondary ion mass spectrometry (SIMS) in

8、 the area of surface analysis. The major differences between XRF and TXRF are related to the form of the sample and its preparation and the nature of the calibration and quantification procedures. The instrumental detection limits currently achievable with TXRF lie below 10-12g or 1010atom/cm2, i.e.

9、 orders of magnitude lower than for XRF. These differences lead to a variety of fields of application for TXRF in the areas of microanalysis and trace analysis as well as surface analysis. Although the abbreviation TXRF is used consistently in this document because of its international character, th

10、e abbreviation TRFA is equally valid in the German-speaking domain as it has the same meaning as the English term and is, moreover, already used in DIN 51418-1. DIN 51003:2004-05 1 Scope This standard specifies definitions for analytical methods with which elements are identified and their concentra

11、tions determined via measurements of X-ray emission or fluorescence. The purpose of this standard is to establish definitions for TXRF and to match these with definitions relating to the various areas of optical atomic spectral analysis: optical emission spectrometry (OES), atomic absorption spectro

12、metry (AAS) and atomic fluorescence spectrometry (AFS). 2 Normative references This standard incorporates, by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the titles of the publications are listed belo

13、w. For dated references, subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated in it by amendment or revision. For undated references, the latest edition of the publication referred to applies (including any amendments). DIN 5031-8, Physics

14、of radiation in the field of optics and illuminating engineering Definitions and constants of radiation physics DIN 32633, Standard addition methods used in chemical analysis DIN 51009, Optical atomic spectral analysis Principles and definitions DIN 51418-1, X-ray spectrometry X-ray emission- and X-

15、ray fluorescence analysis (XRF) Part 1: Definitions and basic principles 3 General definitions 3.1 X-radiation electromagnetic radiation having an energy of 124 keV e U 0,124 keV, corresponding to wavelengths of 0,01 nm 10 nm according to the equation: chvhUe = where e is the elementary electronic c

16、harge, in C; h is Plancks constant, in keVs; c is the velocity of light, in ms-1; U is the voltage, in kV; is the wavelength of the radiation, in nm; is the frequency of the radiation, in s-1. 4 DIN 51003:2004-05 5 3.1.1 characteristic X-ray emission X-radiation* which is emitted as a result of elec

17、tron transitions between the inner energy levels of the atoms; see Figure 1 3.1.2 Bremsstrahlung X-radiation* that is produced via deceleration of charged particles, in particular electrons, during their passage through material 3.2 X-ray spectrum spectrum over the energy range of the X-radiation* N

18、OTE For the term spectrum, see DIN 5031-8. 3.2.1 X-ray line spectrum (characteristic spectrum) spectrum of the characteristic X-radiation* 3.2.2 Bremsstrahlung spectrum spectrum* of the Bremsstrahlung. The Bremsstrahlung spectrum is continuous and has an upper limit Emax(in keV or kg m2 s2) which is

19、 determined by the energy of the charged particles (electrons). NOTE The Bremsstrahlung spectrum has a maximum in the spectral beam density L (intensity in keV or kg m2 s-2) at an energy in the range 0,5 Emax L 0,7 Emax. 3.2.3 X-ray level the electronic state of an atom following removal of one or m

20、ore electrons from fully occupied shells 3.2.4 X-ray spectral line spectral lines (see DIN 5031-8) in the energy range of X-radiation* 3.2.4.1 satellite lines weak lines in the X-ray spectrum* that do not represent X-ray spectral lines* but are caused by secondary effects in the detector system 3.2.

21、5 designation of an X-ray spectral line labelling of an X-ray spectral line* with the element symbol of the atoms producing the X-radiation together with the symbol indicating the energetic transition according to Siegbahn (see Annex A) 3.2.5.1 designation of the energetic transition according to Si

22、egbahn the Siegbahn symbol (e.g. K1or L3) of an energetic transition (see Figure 1) consists of: the series symbol (i.e. K or L) which indicates the electron shell in which the electron jump takes place. a lower case, Greek or Latin letter, not systematic, but normally associated with the intensity

23、of the X-ray spectral line* within a series, usually with a digital index (i.e. as in 1or 3) that is also associated with the intensity of the X-ray spectral line* within the group of lines defined by the appropriate letter. DIN 51003:2004-05 6 3.2.6 Compton lines broad intensity peaks appearing in

24、the X-ray line spectrum* generated by the incoherent scattering (Compton effect) of the radiation of a neighbouring higher energy X-ray spectral line* by weakly bound electrons The designation is made according to the X-ray spectral line* with an additional index c after the brackets enclosing the s

25、ymbol representing the energetic transition, e.g. Sn(K1)c. 3.2.7 analyte line X-ray spectral line* from the atoms or ions of the analyte* NOTE In TXRF, all analytes are chemical elements. 3.2.8 element profile a complete set of X-ray spectral lines* from one X-ray series of a particular element, e.g

26、. K profile or or L profile from barium 3.2.9 line overlap simultaneous occurrence of X-ray spectral lines* from different analytes with very similar line energies so that the lines appear unresolved in the X-ray spectrum* 3.3 X-ray emission emission of X-radiation*; X-radiation consists of characte

27、ristic radiation produced as a result of ionizing collisions between charged particles or photons and materials; continuous X-radiation* either as Bremsstrahlung* (free-bound electron transitions) or as synchrotron radiation* (free-free electron transitions). 3.3.1 X-ray fluorescence radiation emiss

28、ion* of characteristic X-radiation*, also known as secondary radiation, caused by photons or charged particles 3.3.2 primary X-radiation X-radiation* employed to induce X-ray fluorescence radiation* in a sample* 3.3.3 sample radiation X-radiation* emitted from the sample consisting of X-ray fluoresc

29、ence radiation* and scattered primary X-radiation* 3.3.3.1 fluorescence yield ratio of the number of fluorescence photons to the number of electron transitions NOTE The energy released during an electron transition leads to either the emission of a photon or to the expulsion of an Auger electron. Th

30、e fluorescence yield increases with atomic number. DIN 51003:2004-05 3.3.3.2 signal intensity intensity of an analyte line*, normally given as count rate (impulses per second) 3.3.3.3 signal to background ratio ratio of the signal intensity* to the intensity of the background* within an energy windo

31、w corresponding to the analyte line* under consideration 3.4 background (in TXRF) the sum of all detector artefacts and of all radiation contributions arising from scattering of the primary radiation* or sample radiation from the sample and the sample carrier or in the detector system (spectral back

32、ground) NOTE In the context of X-ray spectrometry, background in the sense of radiation from external sources not associated with the measurement process itself (e.g. cosmic radiation, radioactive materials) is normally negligibly small. 3.5 absorption of X-radiation the absorption of a parallel bea

33、m on transmission through an isotropic and homogeneous medium with parallel sides follows the Bouger-Lambert-Beers law: )exp(01l= where 1is the spectral radiation power behind the absorber*, in W; 0 is the spectral radiation power in front of the absorber*, in W; is the mass absorption coefficient,

34、in cm2 g-1(see Figure 2); is the density of the absorber*, in cm2 g-1; l is the thickness of the absorber*, in cm. NOTE In the context of TXRF, the absorption of X-radiation is only of relevance with regard to two points: the use of a primary beam filter*; the analysis of light elements (Z 20), beca

35、use self-absorption* in the sample can take place. 3.5.1 absorption edges sharp changes in the mass absorption coefficient* at a specific energy that is dependent on the atomic number of the absorber material. An absorption edge occurs if the energy of the incident radiation exceeds the binding ener

36、gy of the electrons in a particular shell in the absorber material, see also Figure 2. 3.6 X-ray spectrometer analytical instrument for the detection and quantitative determination of chemical elements (analytes) on the basis of their characteristic (element-specific) X-ray fluorescence radiation (s

37、ee also DIN 51814-1), consisting of: a primary X-ray source; 7 DIN 51003:2004-05 an X-ray optical system (including monochromator); a sample stage; a detector system; a signal processing unit. 3.6.1 TXRF spectrometer an X-ray spectrometer in which the total reflection* effect is utilized to achieve

38、a large signal to background ratio for applications in microanalysis, trace element and surface analysis 4 Physical principles 4.1 total reflection (in TXRF) the practically complete reflection of electromagnetic radiation propagating from an optically more dense medium into an optically less dense

39、medium at small incidence angles NOTE In the wavelength range of X-radiation*, the refractive index n of all media is n 1 (for vacuum, n = 1) so that total reflection of X-rays can always take place during propagation from the optically less dense medium into the optically more dense medium. In the

40、ideal case, the reflectivity* R increases sharply from about 0 % to 100 % at the critical angle*; in real cases this increase is spread over a certain angular range, see Figure 3. 4.1.1 reflectivity the reflectivity is defined by the Fresnel equation as: 221210R+=IIR where IRis the intensity of the

41、reflected radiation, in Wm2; I0 is the intensity of the original radiation, in Wm2; 1 is the grazing angle of the incident radiation, in ; 2 is the complex refractive angle in the medium, in . The complex angle 2is derived from the definition of the complex refractive index , in which represents the

42、 dispersion term and the absorption term, as: in = 1 i22122= For further details see 1. 4.1.2 critical angle the upper limit on the angle for total reflection (see Figure 3) is given by: 8 DIN 51003:2004-05 mmcrit65,1AZE= where critis the critical angle, in ; E is the photon energy of the radiation,

43、 in keV; Zmis the mean1)atomic number of the medium, i.e. Zm= (XE ZE); Amis the mean1)relative atomic weight of the medium, i.e. Am= (XE AE), in gmol1; is the density of the medium, in gcm3. NOTE Both the critical angle and the grazing incidence angle are often quoted in units of mrad. Conversion fa

44、ctor: 1 = 17,5 mrad. 4.2 sample excitation (in TXRF) generation of X-ray fluorescence radiation* in the sample by irradiating with primary radiation* usually of a selected energy 4.2.1 measurement angle; grazing incidence angle incidence angle of the primary radiation* on the sample carrier* under t

45、he measurement conditions. The measurement angle is normally smaller than the critical angle* because only then can total reflection take place (see Note in 4.1.2). 4.2.2 standing waves electromagnetic field with stationary, time-independent minima and maxima caused by interference between the refle

46、cted and incident waves in a spatially defined region above the reflecting medium (see Figure 4). The intensities can be described by: 02min)1( IRI = 02max)1( IRI += where Imin is the intensity of the radiation in the minima, in Wm2; Imax is the intensity of the radiation in the maxima, in Wm2; I0 i

47、s the original intensity of the radiation, in Wm2; R is the reflectivity. For ideal total reflection the intensity in the minima is zero and the intensity in the maxima is four times greater than the original intensity. 1) Arithmetically weighted mean of the fractional amounts of substances present

48、9 DIN 51003:2004-05 4.2.2.1 period (of the standing waves) the constant spacing between neighbouring minima perpendicular to the surface of the medium, given by: sin2=d where is the wavelength, in nm; is the angle of grazing incidence*. EXAMPLE With typical measurement parameters, i.e. Mo-Kradiation

49、 (17,4 keV, = 0,071 nm) and = 0,057 (1 mrad) the resulting period is 35 nm. 4.2.3 penetration depth the distance from the surface within the reflecting medium at which the intensity of the propagating wave is reduced by absorption* to 1/e of its original value. The decrease in a direction perpendicular to the surface is exponential. NOTE At the critical angle* the penetration depth decreases sharply by orders of magnitude, see Figure 5. 4.3 f