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Figure 7
Optimum photon energy Et (left scale; blue) and per-pixel imaging time Tp (right scale; red) for imaging 20 nm Cu features in Si (a) and 20 nm protein features in a 70% ice/30% protein mixture as tissue (b). The pixel imaging time Tp was calculated according to equation (10)[link], using values of the estimated number of photons [\bar{n}_{\rm pixel}] for a variety of photon energies shown in Fig. 2[link] and the future spatially coherent flux (at 0.1% bandwidth) values shown in Fig. 6[link] for the ALS-U (below 4.9 keV) and the APS-U (at 4.9 keV and above). For each background material thickness value t, the smallest value of Tp is used along with its associated photon energy Et. This per-pixel imaging time Tp is assumed to be equal to the per-voxel imaging time Tv due to dose fractionation as discussed in Section 3.1[link]. Also shown is the energy Eest found by setting μ−1(Eest) of equation (4)[link] equal to the total thickness t of the background material. In practice, one might be able to accept 1% spectral bandwidth and thus reduce the pixel time by a factor of ten, while reflection efficiencies of beamline and nanofocusing optics might increase the pixel time by about a factor of ten. Therefore the pixel time shown here represents a reasonable estimate.

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