Effect of 100°/o He on H5191X/H2431 Photomultiplier Tubes

Abstract

Three photomultiplier tubes, one of fine-mesh type and the other two of conventional type, were placed inside a gas-tight sealed container with 100% helium for about 20 days. After pulses appear and can be seen on the oscilloscope
after some time. They occur at about 250 ns after the main pulse for the c~ventiohal _ tube and at 100 ns for the fine~mesh tube. It was observed tha~ the "Jean ADC distribution tube and 100 ns for the fine-mesh tube. It was observed that the mean ADC distribution of the afterpuls~s increases as the time of exposure to helium is prolonged. It was also found out that the rate of increase of the afterpulse is the same for the fine-mesh tube and the conventional tube.