where η(ε) is the quantum efficiency of the detector and I 0 (ε) is the incident X-ray intensity with the unit of photons per unit area per unit electron energy (photons/(m 2 keV)). The inicident X-ray intensity is a function of X-ray energy (ε). Variations in material properties are more detectable than variations in X-ray energies, particularly when utilizing a synchrotron facility that can generate an almost mono-chromatic X-ray source. Therefore, Tomo-NeRF neglects the incident energy variation and simplifies the Beer-Lambert Law function as only an integral function of penetration thickness: