Development of a high quantum efficiency photo multiplier tube

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Demands for a photo multiplier tube (PM tube) with a high quantum efficiency (Q.E.) are recently increasing in many fields such as the radiation measurement with scintillation counters, the fluorometric analysis, the photon counting measurement, and so on. One of the ways to improve of the Q.E.of a PM tube is to utilize the light which penetrates the photo cathode (P.C.) without producing photo electrons. We have a new idea of using the secondary P.C.and the reflector to make use of the penetrating light. In order to check the efficiencies of this idea, we measured the penetrability, the reflectance, the absorption ratio and the quantum efficiency of the P.C.in the range of the wave length between 250nm and 700nm. The data obtained at 400nm are as follows ;From this result, an improvement of the Q.E.with a factor of 15%-30% is expected with the use of the secondary P.C.and the reflector. It indicates that the secondary P.C.and the reflector are effective for the improvement of the Q.E.. It was also found that the Q.E.depends on the thickness of the P.C., and it should be studied further in order to optimize the effect of the secondary P.C.and the reflector.