Single Hit CCD Spectrometers for X-ray conversion efficiencies

X-ray conversion efficiency is often difficult to obtain given uncertainties of the detector sensitivity. CCD cameras with known distance and attenuation, for which less than one photon is detected per pixel, can provide absolute spectra via the image histogram, but noise, fluorescence, sky-shine, and charge splitting between pixels (“charge bleed”) are challenges. We present new results and explain features that were previously unnoticed. We found that most hits suffer from charge bleed which may be reversed by summing over neighboring pixels, but this process becomes increasingly inefficient at exposures for which charge-bled events overlap, resulting in a continuous background instead of well reconstructed spectral lines. We show compromises for signal strength versus quantitative fidelity, in which conversion efficiencies can be determined despite incomplete charge-bleed reversal. To demostrate the power of the diagnostic, we present the study of conversion efficincies for a laser-driven Cu-K_a source in dependence of laser-incidence angle and detector observation angle.