Performance Characteristics of WDS and EDS Detectors Part 2 EDS

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Performance CharacteristicsofWDS and EDS
DetectorsPart 2 - EDS

• Mike MatthewsAWE

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Outline

• Energy Dispersive Spectrometers
• basic principles
• characteristics
• practical performance
• Summary

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Energy Dispersive Spectrometers

• Principles of operation

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Energy Dispersive Spectrometers

• Principles of operation

GFPC 27.2eV
64 ion pairs
SiK? 1.74KeV
Si(Li) 3.8eV
470 ion pairs
Ge 2.9eV
600 ion pairs
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Energy Dispersive Spectrometers

• Si(Li)
• Intrinsic impurities in pure Si
• Counteraction by Li
• Li drifting
• Advantages
• mechanically simpler
• no de-focussing
• parallel X-ray collection
• simple to apply

Li
Si
Si(Li)
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Energy Dispersive Spectrometers

• Factors Affecting Resolution
• Noise
• Statistical
• Thermal
• Electrical

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Energy Dispersive Spectrometers

• Factors Affecting Resolution
• Incomplete charge collection
• Dead layer
• Trapping

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Energy Dispersive Spectrometers

• Escape Peaks
• Absorption by SiK shell
• Emission of SiK? X-ray
• Poor re-absorption

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Energy Dispersive Spectrometers

• Internal Fluorescence
• Excitation of SiK? in the dead layer
• Lose auger electron
• Absorb SiK? X-ray
• Direct excitation of SiK?
• Background radiation
• Stray electrons
• SiK? peak in spectrum

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Energy Dispersive Spectrometers

• Dead Time
• Pulse process time
• Time Constant
• Count rate
• Resolution

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Energy Dispersive Spectrometers

• Dead Time

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Energy Dispersive Spectrometers

• Dead Time

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Energy Dispersive Spectrometers

• Dead Time
• Time variant pulse processing
• Low noise FETs
• High speed ADC
• Intelligent base-lining

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Energy Dispersive Spectrometers

• Pulse Pile-Up
• Sum peaks
• Reduced parent peak

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Energy Dispersive Spectrometers

• Counter Window

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Energy Dispersive Spectrometers

• Counter Window

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Energy Dispersive Spectrometers

• Counter Window

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Energy Dispersive Spectrometers

• Counter Window

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Energy Dispersive Spectrometers

• Efficiency

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Energy Dispersive Spectrometers

• Silicon Drift Detectors

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Energy Dispersive Spectrometers

• Silicon Drift Detectors

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Energy Dispersive Spectrometers

• Silicon Drift Detectors

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Energy Dispersive Spectrometers

• Silicon Drift Detectors
• Very low capacitance
• Higher energy resolution
• Shorter shaping times
• High count rates
• Very low leakage current
• Only moderate cooling
• Self re-setting anode
• Simple DC voltage to operate
• No detector clock re-set overhead
• Simple robust package

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Energy Dispersive Spectrometers

• Silicon Drift Detectors
• Thin
• gt90 efficiency _at_ 10KeV
• gt50 efficiency _at_ 20KeV
• FET burn
• Pulse pile-up
• ICC
• Low energy performance
• Ballistic deficit

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Energy Dispersive Spectrometers

• Summary
• Simple to apply
• Parallel acquisition
• Virtually no pre-configuration
• No De-focussing
• Poor resolution
• Overlaps
• Detection limits
• Poorer accuracy and precision
• Spectrum artefacts
• Escape peaks
• SiK? peak
• Sum peaks

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End of Part 2Thank you for your attention