  We demonstrate enhancement of X-ray excited optical luminescence in a
100-micron-thick diamond plate by introduction of defect states via electron
beam irradiation and subsequent high-temperature annealing. The resulting X-ray
transmission-mode scintillator features a linear response to incident photon
flux in the range of 7.6$\times$10$^8$ to 1.26$\times10^{12}$ photons/s/mm$^2$
for hard X-rays (15.9 keV) using exposure times from 0.01 to 5 s. These
characteristics enable a real-time transmission-mode imaging of X-ray photon
flux density without disruption of X-ray instrument operation.
