Radiation Damage on X-Ray CCDs and Restoration Technique for Space Astronomy
Radiation Damage on X-Ray CCDs and Restoration Technique for Space Astronomy
复制标题
X射线CCD辐射损伤及空间天文修复技术
DOI：
10.1093/pasj/49.3.405
复制
发表时间：
1997
影响因子：
2.3
通讯作者：
Koei Yamamoto
中科院分区：
文献类型：
--
作者：
H. Tomida;H. Matsumoto;M. Ozaki;Y. Tazawa;H. Awaki;T. Tsuru;K. Koyama;H. Tsunemi;Koei Yamamoto
我们研究了X射线CCD的质子损伤效应，并寻找可能的在轨修复技术。我们测量的X射线CCD性能照射后，在2和9.5 MeV的能量，并确认了一个明确的退化的电荷转移效率（CTE）和能量分辨率。为了恢复退化的CTE和能量分辨率，我们尝试了电荷注入技术，并且发现CTI（= 1 - CTE）和能量分辨率的改善分别为1/4和1/3。我们还估计了深阱的能级，这导致了辐射损伤像素的暗电流的量化。陷阱能级约为0.57eV，接近禁带中心。主要工作：仪器：探测器-X射线：一般-X射线：光谱1. 1993年2月20日发射的第四颗日本X射线天文卫星ASCA（宇宙学和天体物理学高级卫星）上的固态成像光谱仪（SIS）是第一台用于X射线天文学的CCD相机（Tanaka等人，1994年）。在6 keV的~ 2%的高能量分辨率，~ 27 fim的位置分辨率和0.5 - 10 keV的宽能带肯定开辟了一个新的窗口的X射线天文学，特别是关于方面的X射线成像和光谱学。因此，我们相信X射线CCD应该进一步改进，作为未来X射线天文学的标准探测器。考虑到这一点，我们目前正在与空间和宇航科学研究所（IS AS）的合作者开发X射线天文卫星上的X射线CCD相机。经过几年的ASCA在轨运行，我们发现CCD的性能显着下降，这主要是由于粒子（质子）的照射，而在轨道上。最严重的问题是暗电流的增加和电荷转移效率（CTE）的降低。C T E的任何不均匀性都会影响能量分辨率。1 CCD模式的能量分辨率从发射后的约130 eV下降到在轨2.5年后的250 eV（Dotani等人，1995年）。这些问题最终决定了X射线CCD仪器的科学寿命。因此，研究质子在X射线CCD中引起损伤的物理过程，寻找一种使质子损伤效应最小化的工作条件是十分重要的。同时，也迫切需要建立一种实用的在轨方法来恢复质子损伤的性能。我们一直在努力研究上述问题（特别是恢复方法）。本文给出了我们的实验结果和总结。这些结果将纳入定于2000年2月发射的下一颗卫星ASTRO-E的X射线CCD照相机XIS（X射线成像光谱仪）的设计中。这项研究的范围正在扩大到下一代X射线成像和光谱仪器在21世纪。2.对于实验，我们使用由Hamamatsu Photonics K.K.（HPK）。CCD规格总结见表1。CCD由日本天文学会（Astronomical Society of Japan）提供，由NASA天体物理数据系统406 H提供。Tomida等人[第49卷，表1. HPK CCD规格。像素尺寸像素格式耗尽层垂直时钟相位水平时钟相位CCD配置12 jLim x 12 fim 512 x 512 6 fim 2 phase 2 phase full frame transfer
We studied the proton damage effects of the X-ray CCD, and searched for a possible restoration technique in orbit. We measured the X-ray CCD performances after irradiation at energies of 2 and 9.5 MeV, and confirmed a clear degradation of the charge transfer efficiency (CTE) and the energy resolution. To restore the degraded C T E and energy resolution, we tried a charge injection technique, and found the improvement in the CTI ( = 1 — CTE) and energy resolution to be 1/4 and 1/3, respectively. We also estimated the energy level of the deep t rap , which causes a quantization of the dark current from the radiation-damaged pixels. The t rap energy level was about 0.57 eV, or near to the center of forbidden band. K e y w o r d s : Instruments: detectors — X-rays: general — X-rays: spectra 1. I n t r o d u c t i o n The solid state imaging spectrometer (SIS) on-board the 4th Japanese X-ray Astronomical Satellite ASCA (Advanced Satellite for Cosmology and Astrophysics), launched on 1993 February 20, is the first CCD camera for X-ray astronomy (Tanaka et al. 1994). A highenergy resolution of ~ 2% at 6 keV, a position resolution of ~ 27 fim and a wide energy band of 0 .5 10 keV certainly opened up a new window of X-ray astronomy, particularly concerning the aspects of X-ray imaging and spectroscopy. We therefore became confident tha t X-ray CCDs should be further improved as a s tandard detector in future X-ray astronomy. Wi th this in mind, we are currently developing X-ray CCD cameras on-board an X-ray astronomical satellite, with collaborators at the Insti tute of Space and Astronautical Science (IS AS). After a few years of the ASCA in orbit operation, we found a significant degradation of the CCD performance, which was mainly caused by particle (proton) irradiation while in orbit. The most serious problems are an increase in the dark current and a decrease in the charge transfer efficiency (CTE). Any non-uniformity of C T E worsens the energy resolution. The energy resolution in the 1 CCD mode was degraded from ~ 130 eV just after the launch to 250 eV after 2.5 years in orbit (Dotani et al. 1995). These problems eventually determined the scientific lifetime of the X-ray CCD instruments. Thus, it is essentially important to study the physical process of proton-induced damage in the X-ray CCD and to search for an operation condition which minimizes the proton damage effects. Also, it is highly required to establish a practical in-orbit method to restore the proton-damaged performance. We have been trying to investigate the abovementioned issues (especially recovering method) . This paper gives the results and a summary of our experiments. These results will be incorporated in the design of the X-ray CCD camera XIS (X-ray Imaging Spectrometer) for the next satellite, ASTRO-E, to be launched in 2000 February. The scope of this study is being extended to a next-generation X-ray imaging and spectroscopy instruments in the 21st century. 2. E x p e r i m e n t s For the experiments, we used an X-ray CCD produced by Hamamatsu Photonics K.K. (HPK). The CCD specifications are summarized in table 1. The CCDs were © Astronomical Society of Japan • Provided by the NASA Astrophysics Data System 406 H. Tomida et al. [Vol. 49, Table 1. HPK CCD specification. Pixel size Pixel format Depletion layer Vertical clock phase Horizontal clock phase CCD configuration 12 jLim x 12 fim 512 x 512 6 fim 2 phases 2 phases full frame transfer