X-Ray Fluorescence Detectors: Silicon Drift (SDD) v PIN-Diode (Si-PIN)

Most lines of XRF Spectrometers will typically offer a model with a proportional counter detection system (for basic coating thickness measurements) and have additional systems with higher resolution detector technology, either Silicon Drift Detection (SDD) or Si-PIN Diode Detectors (Si-PIN) for elemental analysis interests.  Both SDD and Si-PIN detector technologies offer benefits to the end users and the following offers a brief overview and comparison
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OBJECTIVE
To perform a quantitative comparison between the performance of an XRF Spectrometer with a SDD detector installed or a Si-PIN detector.  The sensitivity and performance at different energies when equipped with different detectors is expressed in the minimum detection limits (MDL) of the different elements.

SDD versus Si-PIN Diode
Desktop x-ray fluorescence analyzers for elemental analysis have traditionally been equipped with Si-PIN detectors that provided outstanding resolution and count rate capacity at the time.  However, since Silicon Drift Detectors (SDD) were introduced they have become the ‘detector of choice’ for many material analysis applications.

Si-PIN technology offers an economical detection system which, in turn, allows for a lower priced analyzer.  They also offer a larger active area and thicker depletion depth.  When resolution is critical but high detection efficiency is not as important, the Si-PIN system will be suggested.  However, SDD technology in X-Ray Fluorescence offers a much better energy resolution at short peak times; which is helpful at high count rates and can lead to lower limits of detection.

ANALYTICAL CONFIGURATION

ED-XRF Spectrometer for Material AnalysisInstrument: ED-XRF Spectrometer
Anode: Rh-Anode X-ray Tube, 50W
Detector: VARIABLE of SDD or Si-PIN
Analysis Time: 300 seconds per measurement
Goal of Analysis: Determine minimum detection limits
Sample Overview: Liquid Samples, no preparation

SAMPLES
A variety of sample solutions were used to determine the MDL; including water, diesel and oil solutions; some include:
–  Certipur Zinc Standard Solution; 1000mg/l, MERK
–  5.6% Na in water (in-house standard)
–  VHG Labs Sulfur in #2 diesel, 1000ppm

Measurement times were set for 300 seconds.  Typical conditions were air but light element information was aquired using a helium purge.  Tube filters varied according to the sample and element of interest.

MINIMUM DETECTION LIMITS
A detailed overview of the MDL determination can be reviewed in the full comparison sheet but a few example results including:
Element     MDL SDD ppm     MDL Si-PIN ppm
Na               700                        1,600
S                 1.3                           3.2
Zn               0.3                           1.0

Graph of MDL measured with SDD and Si-PIN detectors (S to Ba only)
Detection Limits of XRF Detectors

DISCUSSION
The comparison shows that the main advantage that SDD provides is the ability to acquire spectra at very high count rates without compromising on the resolution.  In this review, it is obvious that the high count rate is key to the low minimum detection limits obtained with the Silicon Drift Detector (SDD).  That being said, the Si-PIN compares favorably with elements that have higher energy and it allows for a lower analyzer cost.

Learn More: intro to the Vortex Detector by Hitachi

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to discuss the available detection systems and elemental analyzers

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