Improvements in SDD Effi ciency
high counts rates, rates that were previously impossible. The ultimate throughput of X-ray counts in a system is dependent on the time to process an X-ray pulse ( Figure 6 )—the shorter the amp processing time, the higher the throughput. Each processing time will have a maximum throughput (the top of each curve in the figure). These high-throughput count rates now permit high-speed X-ray mapping with input count rates over 750 kcps. This means the acquisition of a spectrum image that traditionally took hours can now be acquired in minutes. Instrumentation . T e benefi ts and the improved perfor- mance of the new SDD systems can clearly be seen when the advances are applied to typical analytical examples. T e data presented here were collected using a JEOL 7000F SEM with an EDAX Octane Elite Super detector with a silicon nitride window
and a CUBE amplifi er. To illustrate high-speed mapping, we used an epoxy-embedded, cross-sectioned and polished, cast-steel L profi le with compositional variations at the bend of the L. To show quantifi cation reproducibility and light-element sensitivity at high count rates, we present data from a Ti-6Al-4V alloy and a tool steel with a low C concentration.
Results
High-speed X-ray mapping . In the past handling high count rates typically meant sacrifi cing spectral resolution and light-element performance, resulting in data of limited use. However, with modern detectors capable of very high count rates, acceptable qualitative and quantitative data can be acquired in extremely short times. Figure 7 shows a group of X-ray maps acquired with average ICPS of 844 kcps going up
Figure 7 : A selection of X-ray element maps acquired from a steel L profi le with an average input count rate of 884 kcps at 0.12 µs amplifi er processing time. (a) Phase map showing steel (yellow) and a Ni-rich inclusion (blue). Inside the Ni-rich inclusion, a Mo-rich phase is shown in bright purple and yellow phase, and a Si-rich phase is shown in cyan. The epoxy embedding material (green) is carbon-rich. (b) Fe map. (c) Mo map. (d) C map. Image width = 800 µm.
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www.microscopy-today.com • 2017 March
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