Table II: Limits of detection (ppm) for detectors available on Orbis

The additional solid angle of the 50 mm² detector yields improvements in speed and sensitivity in analytical problems where the 30 mm² detector would be signal starved. When a detector is signal starved, the detector's processing electronics still have available capacity to process more signal. In these cases, having a detector with a greater solid angle allows for more X-ray signal to be passed to the processing electronics. As long as the larger SDD's spectral resolution and throughput are similar to that of the smaller SDD, which is the case here, improvements in speed and sensitivity can be achieved with the larger detector. Typical materials analysis problems which fall into this category include measurements of light element matrices such as glasses, plastics, and aluminum alloys; measurements of trace elements where heavier filters are needed for best sensitivity such as trace Pb and Cd in solders and plastics and measuring thin residues, corrosion, and coatings on light element matrices. Table II compares the limits of detection for several elements spanning the XRF spectral range.

For the data collected in Table II, the SDD detectors were operating in the signal starved regime where the X-ray tube is run at full power for maximum excitation. Improvements in sensitivity of the 50 mm² over the 30 mm² SDD are approximately consistent with the increase in solid angle of the 50 mm² over the 30 mm² SDD.

In applications where improved sensitivity is not needed, the 50 mm² SDD can be used for increased productivity. The proportionality between sensitivity as described by the limit of detection (LOD) and measuring time is shown in equation 2.

Hence, the increased sensitivity provided by the 50 mm² SDD can be traded for faster measuring time. For example, using equation 2 and the improvements in measuring sensitivity shown in Table II, the 50 mm² SDD can achieve the same measurement sensitivity obtained with the 30 mm² SDD with a nominal 40% reduction in measuring time.