Development of an X-ray Poralimeter Using Direct X-ray Imaging CCD with Position, Energy and Time Resolution

本研究项目的目的不仅是为了提高X射线CCD的基本性能，而且是为了提高其作为X射线偏振器的性能。研究小组由滨松光子学(HPK)的S成员和大阪大学的成员组成。根据所有成员确定的规格，在HPK制作了CCD芯片，由大学方对这些芯片进行操作和检查，并使用不同的材料和制作方法制作了几种不同种类的CCD芯片。采用像素尺寸为12微米、像素数为512×512的CCD芯片，最终获得了对5.9keV X射线的140 eV能量分辨率。虽然第一年年底的分辨率为160 eV，但暗电流降低1/50会导致更好的分辨率。利用高灵敏度材料，得到了耗尽层厚度为20 mm的CCD芯片。大学方面的活动包括：1)测量0.4-2.2keV X射线的CCD探测效率的光谱仪系统；2)抑制杂散电荷噪声的CCD驱动时钟；3)基于DSP的高速读出系统；4)CCD内部X射线吸收和电荷收集过程的模拟程序。此外，我们还发明了一种通过在芯片前设置网格来测量亚像素结构探测效率的新方法。我们还测量了实验室X射线发生器产生的X射线束的偏振度。已开始制作像素尺寸为6微米的可用于X射线偏振测量的CCD芯片。这些小像素尺寸的电荷耦合器件的偏振能力将在1997年内进行测试。

The purpose of this research project is to improve not only the fundamental properties of X-ray CCD but also as an X-ray polarimeter. The research group consists of the member s in Hamamatsu photnonics (HPK) and the members in Osaka university. According to the specification determined by all the members, the CCD chips were fabricated at HPK,and the university side operated and examined those chips.Several kinds of CCD chips using different material and production methods have been made. We got eventually energy resolution of 140 eV for 5.9 keV X-rays with a CCD chip of which pixel size is 12 mum and pixel number is 512x512. Although the resolution was 160 eV at the end of the first year in the research term, reduction of the dark current by 1/50 lead to the better resolution. Using high registivity material, we got a CCD chip of which depletion layr is as thick as 20 mum.University side activities include the development of CCD operation and evaluation ; 1) spectrometer system for measuing the CCD detection efficiency for 0.4-2.2keV X-rays, 2) CCD drive clock to suppress spurious charge noise, 3) high speed read-out system using DSP,4) simulation code for X-ray absorption and charge collection process within CCD.Adding these, we invented a novel method for measuring detection efficiency for sub-pixel size structure by employing a mesh in front of the CCD chip. We also measured polarization degree of the X-ray beam from a laboratory X-ray generator. CCD chips with pixel size of 6 mum, which should be effective for X-ray polarimetry, were started to fabricate. The polarimeter-capability of those small pixel size CCD will be measured within the year of 1997.