Saving the photons: mapping x-rays by position-tagged spectrometry

Since the early years of Ii-ray spectrometry in electron microscopes, mappi ng the locations of chemical elements has been important. The X-rays needed in large numbers for this are rare, owing to poor production efficiency co mpared with electron signals, and at risk of loss by many mechanisms such a s missing the limited solid angle of the detector, absorption before reachi ng the detector and pulse pile-up conventional digital mapping hardware red uces the information contained in the X-ray spectrum at each pixel to the i tegrated counts from a few regions of interest. The acquisition technique of position-tagged spectrometry eliminates the co nflict between the desire to see full frame Ii-ray images quickly versus th e analytical advantages of having complete spectra for each pixel. As the b eam is scanned rapidly relative to traditional Ii-ray mapping, photons are counted in a virtual 3-D multichannel analyser on disk, preserving both spa tial and spectral information. Along with the sophisticated post-processing allowed by storing an entire spectrum per pixel, a unique degree of dynami c interaction with the developing data is made possible by integrating many short scans instead of using a single long dwell time at each pixel.