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Figure 4
Total spectra from the sample and emission spectra for different elements. The element spectra are from the middle of the sample only. The total signal includes absorption effects from the sample as the signal goes through. Simulations were done with 1019 W cm−2. The samples are (a) lysozyme (Lys+B1), (b) NaCl buffer (B1), (c) photosystem I (PS I+B2) and (d) photosystem I where the methionine S atoms have been exchanged with selenium. Above 1 keV, the heavier elements have emission lines beyond the black body background (the temperature is the same for all ions). The selenium substitution shows the possibility of biochemically adding new spectral features, with selenium (in blue) different from sulfur (in yellow). Note that the scale is in emitted photons per energy unit, to emphasize that the emitted number of photons at high energy could be considerable.

IUCrJ
Volume 4| Part 6| November 2017| Pages 778-784
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517014154