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光阴极由衬底(包括介质阴极的导电基底)和光电发射膜构成。采用了聚丙烯、Formvar和Paylene三种有机薄膜作阴极衬底。建立了这些薄膜的制备技术。用一台自制的软X射线单色仪在277—7469ev光子能量范围内测量了这些薄膜的透过率。 研究了CsI、CsBr、Au和MgF_2四种光电阴极的光电发射特性和光电发射与阴极厚度的关系,找出了最佳阴极厚度。用软X射线单色仪在277—7469ev光子能量范围内测量了最佳厚度阴极的绝对量子效率,四种阴极最大值分别为4.50、2.90、0.25和0.12。我们还在同一阴极衬底上分区制备了四种阴极,在变象管荧光屏上比较其亮度,结果和测量的一致。 用LAB5型表面分析仪对CsI和Au阴极的光电子初能量分布作了测量,CsI阴极光电子初能量分布半高宽远小于Au。因此CsI是适用于高速摄影变象管比较理想的软X射线光电阴极。
The photocathode is composed of a substrate (a conductive substrate including a dielectric cathode) and a photoemissive film. Using polypropylene, Formvar and Paylene three kinds of organic films for the cathode substrate. The preparation techniques of these films were established. The transmittance of these films was measured with a home-made soft X-ray monochromator at a photon energy range of 277-7469 ev. The photoelectric emission characteristics of CsI, CsBr, Au and MgF 2 photocathodes and the relationship between photoelectric emission and cathode thickness were studied, and the best cathode thickness was found out. The absolute quantum efficiency of the cathode with the best thickness was measured with a soft X-ray monochromator at a photon energy range of 277-7469 ev. The maximum values of the four cathodes were 4.50, 2.90, 0.25 and 0.12, respectively. We also prepared four cathodes on the same cathode substrate, comparing their luminosity on a vial screen, with the same results as the measurements. The initial energy distribution of photoelectrons in CsI and Au cathodes was measured by LAB5 surface analyzer. The initial energy distribution of CsI cathodes was much smaller than that of Au. So CsI is suitable for high-speed photogram tube ideal soft X-ray photocathode.