  Conventional x-ray imaging detectors suffer from parallax error when the
radiation beam arrives at the detector surface at tilted angle. The image
blurring occurs as the radiation penetrates detector material in lateral
direction at tilted angle. However, at the photon energies used in x-ray
microscopy the attenuation length of the x-rays in the detector material is
shorter and consequently the parallax error due to the tilted angle irradiation
can be smaller. In these cases, the tilted angle irradiation can be beneficial
because it will expand the beam projection ("footprint") at the detector
surface, improve spatial resolution and help to overcome inherent resolution
limit of the detector. We have performed a simulation study to investigate the
above trade-off between the parallax error and improved spatial resolution when
tilted angle irradiation is used. Our simulation study showed that tilted angle
irradiation at 2-5keV x-ray energies can provide substantial improvements of
spatial resolution. We used in our studies the indirect-conversion x-ray
microscopy detectors based on scintillators optically coupled to CCD and CMOS
cameras, as well as direct-conversion detectors based on back illuminated (back
thinned) CCD and CMOS cameras. We have demonstrated also that the tilted angle
irradiation can prevent radiation damage of the direct conversion back
illuminated CCD and CMOS cameras due to the shallow x-ray attenuation depths
with tilted angle geometry.
