Improvement of the position resolution of the CCD for X-ray use

The authors report here experimental results relating X-ray interaction location and event splitting. The X-ray interaction location can be localized at subpixel scale using the mesh technique. The authors found that the center of gravity of the split event is well-correlated with the X-ray interaction location. They analyzed the data using two models for the charge cloud shape: one is the rectangular model and the other is the Gaussian model. Although the authors could not distinguish between these models, they measured a root mean square charge cloud size of 1 to 2 /spl mu/m for X-rays of Y-L (1.9 keV), Ag-L (3.0 keV), and Ti-K (4.5 keV). When the X-rays enter near the pixel boundary, the charge splits into adjacent pixels, allowing determination of the X-ray interaction location with an accuracy of 1.5 to 2.2 /spl mu/m. The authors, therefore, expect that the X-ray CCD can function as an X-ray imager with subpixel resolution, which will be especially useful in applications involving very high spatial resolution optics.