Development of an X-ray Spectrometer with Sub-Micron Spatial Resolution

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We have studied methods to improve the spatial resolution of the X-ray CCD detector as a spectrometer. The spatial resolution of X-ray CCD is determined mainly by (1) pixel size of the CCD, (2) noise of the measured pulse heights, and (3) data processing algorithm. Among these, we concentrated on items (2) and (3), because the development of CCD with small pixels is beyond the scope of current research.Both the clock signals and the analogue electronics are keys to reduce the noise of the pulse heights. We adjusted the phase of the clock signals and the sampling timing to minimize the interference of the clocking noise to the output. We developed a low-noise preamplifier and an active low-pass filter to improve the signal-to-noise ratio of the analogue circuits. With these modifications, we could reduce the measurement noise significantly. We also studied the best algorithm to determine the incident position of X-ray photons from the distribution of measured charges. We found that just a simple model fitting with a 2-dimensional Gauss function gives a good result.We could determine the incident position of X-ray photons with an accuracy of about 20% of the pixsel size. We estimate that the position error can be reduced to 10% with further improvement of S/N ratio. CCDs with pixel size smaller the 10 μm are now available for X-ray detection. With these CCDs it is possible to achieve a spatial resolution less than 1 μm. This is the goal of our research.