M4 TORNADO, 2D µ-XRF, Ultimate Speed and Accuracy

Analytical Performance

The analytical performance of Micro-XRF instruments depends on the measurement conditions. Parameters have to be selected carefully according to the required task:

 

Spatial resolution

The spatial resolution of a position-sensitive measurement is influenced by different factors like spot size, step size, and measured intensity.

Spot size
The spot size is one of the main factors that influence the spatial resolution of images. It is usually measured with the knife edge method. This technique measures the beam intensity as a function of the position will performing a line scan across the shap edge of a material.

Step size
Other factors influencing the spatial resolution of elemental distribution images are the pixel size and the contrast between pixels. In Micro-XRF the pixel size is determined not only by the spot size but also by the step size. The spatial resolution can be improved if the step size is smaller than the spot size. On the other hand, a minimum level of intensity is required for good contrast between neighboring pixels. The pixel intensity can be changed by varying the acquisition time per pixel. According to these facts, the step size and the pixel intensity have to be optimized for a given spot size.

 

Limits of detection

The sensitivity of Micro-XRF is comparable to that of conventional energy dispersive XRF (ED-XRF). It is determined by the excitation probability of the analyte and the peak-to-background-ratio. When performing Micro-XRF, the transmission function of the X-ray optics must also be taken into account, apart from the tube spectrum. This influences the limits of detection (LOD) for elements with low and high excitation energies. The LOD are low when compared to conventional ED-XRF.

 

Light element detection

Light elements have low fluorescence energy, for which absorption is high, even in air. Therefore the measurement of these elements should be performed in vacuum.

M4_Si_peak.jpg
Comparing the height of a Si peak under vacuum (blue) and in air (red)

Download the full lab report XRF 442 (PDF)