Development and Prototyping of a Digital Pulse Processor for Improved Coincidence Detection, Rejection, and Pulse Recovery, for High Count-Rate Silicon Drift Detectors

The recent emergence of the Silicon Drift detector (SDD), for use in energy dispersive x-ray spectrometry (EDS), has made possible x-ray event streams with count rates as high as 1-10 Mcps. A problem with existing digital signal processing, as applied to SDDs, is the significant presence of coincidence peaks above the x-ray background. These coincidence peaks occur with amplitudes comparable to low-concentration species. In specimens with x-ray peaks arising from two or more elemental constituents, the coincidence peaks can occupy a sizeable portion of the spectrum between the high abundance peaks, leading to false identification of elements and significant errors in quantification. NIST seeks advanced digital signal processing techniques to overcome this severe limitation to SDD application. The objective of the Phase II work is to provide NIST a prototype digital pulse processor that demonstrates an order-of-magnitude reduction in coincidence counting, at an output count rate of 500,000 cps. Our Phase I work and continuing development in anticipation of a Phase II award suggest that the requirement can be met and likely exceeded, with the additional bonus that other parts of the event stream can also be recovered instead of rejected, leading to significant improvements over current state-of-the-art pulse processing.