Development of a photon detector using capillary plates

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It was found in a resent research that the resistance of the capillary plates can be adjusted by change the degrees of deoxidization of the lead glass, and the diameter and the thickness of the capillary plates. After the adjustment of these parameters a big gas gain was obtained with the capillary plates. It was found that a quantum efficiency of the K-Cs photocathode placed in an argon+methane gas which is used in actual MWPC was very stable (about 15%) during a few days measurement. It was also true for an argon+CF4 gas.On the other hand, it was pointed out that a degradation of the photocathode may happen due to an ion feedback during a gas amplification process. In order to overcome this problem we have introduced a capillary plates with a bias angle. Choosing an appropriate bias angle, we can make such that only electron passes the capillary holes while the ion can not, since in the space where an electric field and a magnetic field were applied vertically each other, the Lorentz … More angles differ for the electrons and the ions. When examining the effect actually, it found that the ion feedback was excellently restrained. This result was already reported in an international conference in Vienna.In the recent work it was found that a stable high gain operation is possible in a gas chamber combined with capillary plates and Micromegas detector. We actually manufactured this type gas chamber and coupled with a transparent type K-Cs photocathode. We tried to observe visible light by using this gas chamber, however, we could not see any signals. We can explain this failure in such a way that the alkali metals used for the photocathode have reacted with the lead glass in the capillary and it changes the resistance of capillary plates. Therefore we removed the capillary plates from the chamber and tried with only Micromegas. Then we succeeded in observing a clear signal of gamma rays from a 137Cs source using NaI scintillator for the first time in the world. We reported this result, too, in the international conference.We are continuing this study by changes the material of capillary plates into the soda glass from the lead glass and plan to do a test. Less