X-ray fluorescence microscopy exposure estimates using a single excitation energy

Roter, B.; Crawford, A.M.; O'Halloran, T.V.; Jacobsen, C.

doi:10.1107/S1600577526004923

Figure 1
Combined false color maps and contour plots of the expected minimum number of incident photons $[\bar{N\,}\!_{{\rm inc}}]$ per pixel (a) and skin dose D_skin in Gray imparted (b) for element detection in vacuum. These values are shown versus trace element atomic number Z and individual incident photon energies E_inc. These calculations were carried out for a limit of detection of $[\rho_{\min}^{\prime}]$ = 0.05 µg cm⁻² and for the detection of $[\bar{N\,}\!_{{\rm fluor}}]$ = 5 X-ray photons per pixel summed over all accessible K and L fluorescence emission lines. We assumed that the X-ray fluorescence detector was windowless and had a solid angle of collection of Ω = 1.35 sr. The skin dose D_skin (b) associated with $[\bar{N\,}\!_{{\rm inc}}]$ was calculated assuming a model protein composition of H_48.6C_32.9N_8.9O_8.9S_0.6 (London et al., 1989

) and a focused beam diameter of d_beam = 40 nm. These calculations included all the effects related to photoionization partial cross sections as described in Section 3.1

. As Z increased, the contributions to $[\bar{N\,}\!_{{\rm inc}}]$ and D_skin for a particular subshell abruptly changed when E_inc hit and exceeded that subshell's absorption edge (labeled `thresh.'). The white regions in each panel exist due to an individual value of E_inc not being high enough to excite the L₃ subshell, as well as due to the exclusion of XRF events stemming from shells greater than L₃ from our calculations. This calculation employed tabulated data from xraylib (Schoonjans et al., 2011

). Contour values correspond to base-10 exponents.

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ISSN: 1600-5775

Volume 33| Part 4| July 2026|

https://doi.org/10.1107/S1600577526004923

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