Sealed X-ray framing tube with CsI photocathode to achieve high detection efficiency and stability
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摘要: 为解决采用Au光电阴极、开放式结构的分幅变像管探测效率低、稳定性差的问题，研制了一种采用CsI光电阴极的密封式分幅变像管。为了对比不同光电阴极对X射线的响应强度，密封式分幅变像管制作有一条Au微带阴极和一条CsI微带阴极。完成了密封式分幅变像管的结构设计、工艺制作和实验测试。研究结果表明：当加载半高宽度200 ps、幅值−2.7 kV的选通脉冲时测得其时间分辨为65 ps；在非单色高能X射线源照射下，CsI阴极的静态响应强度是Au阴极的3.4倍；大气环境中存储1000 h后密封式分幅变像管的静态响应强度仅降低到完成制作时的83%。上述结果表明采用CsI阴极的密封式分幅变像管具有更高的探测效率和稳定性，可有效提升X射线分幅成像质量和可靠性。Abstract: A hermetically sealed X-ray framing tube with CsI photocathode is proposed to solve the problems of poor stability and low detection quantum efficiency brought by the open structure framing tube with Au photocathodes. Two microstrip photocathodes of 100 nm Au and 100 nm CsI are fabricated to compare their sensitivities under the same environmental conditions. The structure and the fabrication process of the sealed framing tube are described inthispaper. After fabrication, the sealed framing tube is tested to verify its performance. The measurement shows that exposure time of the proposed framing tube is 65 ps when gated by an ultrafast pulse with 200 ps width and −2.7 kV amplitude. At static mode, the image intensity of the CsI photocathode is 3.4 times that of the Au photocathode under the irradiation of non-monochromatic high energy X-ray source. Its static response intensity is reduced to 83% compared with the initial value after being stored in the laboratory air for 1000 h. These results indicate that the sealed framing tube with CsI photocathode can achieve higher detection efficiency and stability, and can effectively improve the quality and reliability of X-ray framing imaging.
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Key words:
- framing camera /
- X-ray detector /
- ultra-fast diagnostics /
- fusion diagnosis /
- CsI photocathode
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图 1 不同厚度的铍窗对X射线透过率与X射线光子能量的关系曲线
Figure 1. Transmittance of Be window with different thickness as a function of X-ray photon energy
图 2 反射式CsI阴极归一化量子效率随阴极厚度的变化关系
Figure 2. Normalized yield of reflection mode CsI photocathode as a function of cathode thickness
图 5 完成研制的密封式分幅变像管（a）和皮秒分幅相机电控系统（b）
Figure 5. Sealed X-ray framing tube (a) and electric control system (b)
图 7 分幅变像管时间分辨测试结果，其曝光时间为65 ps
Figure 7. Measured temporal resolution of X-ray framing tube, the measured exposure time is 65 ps
图 10 （a）CsI阴极密封式分幅变像管静态响应强度随存储时间的变化关系和（b）Au阴极开放式分幅变像管静态响应强度随累计大气暴露时间的变化关系
Figure 10. (a) Normalized intensity of sealed X-ray framing tube with CsI photocathode as a function of storage time and (b) normalized intensity of open-structured X-ray framing tube with Au photocathode as a function of accumulated air exposure time
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