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

我们研究了提高X射线CCD探测器作为光谱仪的空间分辨率的方法。X射线CCD的空间分辨率主要取决于(1)像元尺寸、(2)测量脉冲高度的噪声和(3)数据处理算法。其中，我们主要集中在第(2)项和第(3)项，因为小像素CCD的开发超出了当前的研究范围，时钟信号和模拟电子设备都是降低脉冲高度噪声的关键。我们调整了时钟信号的相位和采样时序，以最大限度地减少时钟噪声对输出的干扰。为了提高模拟电路的信噪比，我们设计了一个低噪声前置放大器和一个有源低通滤波器。通过这些改进，可以显著降低测量噪声。我们还研究了从测量的电荷分布确定X射线光子入射位置的最佳算法。我们发现，只需一个简单的模型与二维高斯函数进行拟合就能得到很好的结果，我们可以确定X射线光子的入射位置，精度约为像素点大小的20%。我们估计，随着S/N比的进一步提高，位置误差可以减小到10%。像素尺寸小于10μm的ccd现在可用于X射线检测。有了这些ccd，就有可能获得低于1μm的空间分辨率。这是我们研究的目标。

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.