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Adarsh DubeyIph150012012Advance experimental technique X-RAY FLUORESECENCE

CONTENTSDEFERENCE TO X-RAYSGENERATING X-RAYSGENERATING SECONDARY X-RAYSTHEORY & PRINCIPLEINSTRUMENTATIONSAMPLE PREPRATIONANALYSIS OF SAMPLEAPPLICATIONLIMITATION

DEFERENCE:

X-rays were discovered by Wilhelm RoentgenX-ray region 0.1to100 A

The penetrating power of x-rays depends on energy also, there are two types of x-rays. i) Hard x-rays: which have high frequency and have more energy. ii) soft x-rays: which have less penetrating and have low energy

GENERATION OF X-RAYS

X-rays can be generated by decelerating electrons. X-rays are generated by bombarding a target with an electron beam.Beam of electronsTargetX-raysBLOCK DIAGRAM OF XRAY PRODUCTION

Be WindowSilicone Insulation

Glass Envelope

Filament

Electron beam

Target (Ti, Ag,Rh, etc.)

Copper AnodeHV Lead

XRAY PRODUCTION INSTRUMENT

L ShellK ShellK alphaK betaM ShellL alpha

N ShellL beta

K & L Spectral LinesK - alpha lines: L shell e- transition to fill a vacancy in K shell. Most frequent transition, hence most intense peak. K - beta lines: M shell e-transitions to fill a vacancy in K shell.L - alpha lines: M shell e- transition to fill a vacancy in L shell.L - beta lines: N shell e- transition to fill a vacancy in L shell.

GENERATION OF SECONDARY X-RAYS

1) An electron in the K shell is ejected from the atom by an external primary excitation x-ray, creating a vacancy.

2) An electron from the L or M shell jumps in to fill the vacancy.In the process, it emits a characteristic x-ray unique to this element and in turn, produces a vacancy in the L or M shell.

3) When a vacancy is created in the L shell by either theprimary excitation x-ray or by the previous event, an electron from the M or N shell jumps in to occupy the vacancy. In this process, it emits a characteristic x-ray unique to this element and in turn, produces a vacancy in the M or N shell.

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THEORY & PRINCIPLEXRF works on methods involving interactions between electron beams and x-rays with samples.Made possible by the behaviour of atoms when they interact with radiation.When materials are excited with high-energy, short wavelength radiation (e.g., X-rays), they can become ionized.If the energy of the radiation is sufficient to dislodge a tightly-held inner electron, the atom becomes unstable and an outer electron replaces the missing inner electron.When this happens, energy is released due to the decreased binding energy of the inner electron orbital compared with an outer one.

XRF is a reference method, standards are required for quantitative results.

Standards are analysed

Intensities obtained

Calibration plot is generated (intensities vs. concentration).

XRF instruments compare the spectral intensities of unknown samples to those of known standards.

The emitted radiation is of lower energy than the primary incident X-rays and is termed fluorescent radiation.Because the energy of the emitted photon is characteristic of a transition between specific electron orbitals in a particular element, the resulting fluorescent X-rays can be used to detect the abundances of elements that are present in the sample.

BASIC PRINCIPLE:

INSTRUMENTATION

Basic instrumentation

TWO DIFFERENT KIND OF XRFWavelength Dispersive WDXRF SpectrometerEnergy Dispersive EDXRF Spectrometer

CollimatorsCollimators are usually circular or a slit and restrict the size or shape of the source beam for exciting small areas in either EDXRF or WDXRF instruments..

Sample

Tube

Source FiltersFilters perform one of two functionsBackground ReductionImproved Fluorescence

DetectorX-Ray SourceSource Filter

Secondary TargetsSampleX-Ray Tube

Detector

Secondary Target

The x-ray tube excites the secondary target.The secondary target fluoresces and excites the sample.The detector detects x-rays from the sample.

DetectorsSi(Li) -EDXRFPIN Diode-EDXRFSilicon Drift Detectors-EDXRFProportional Counters-WDXRFScintillation Detectors-WDXRF

PN-Detector Principles

A detector is composed of a non-conducting or semi-conducting material between two charged electrodes.

X-ray radiation ionizes the detector material causing it to become conductive, momentarily.

The newly freed electrons are accelerated toward the detector anode to produce an output pulse.

An ionized semiconductor produces electron-hole pairs, the number of pairs produced is proportional to the X-ray photon energy.

SAMPLE PREPRATIONPowders: Grinding (