A Secondary-Emission Electron Multiplier Tube for the Detection of High Energy Particles

The requirements of high gain and low background current in an electron-multiplier tube for the direct detection of high energy particles are considered. The design and construction of an experimental electron-multiplier tube with a stable over-all gain of at least 108 and a background at room temperature corresponding to three or four electrons per minute released at the input is described. An 0.0008-inch thick nickel window is provided in the tube envelope to admit the high energy particles to the multiplier. The efficiency of this device is compared quantitatively with that of a Geiger tube as a detector of beta-particles. It is found that the over-all beta-particle counting efficiency of the tube is of the order of 1.3 percent, and that the efficiency of the oxidized silver magnesium target surface is 4.9 percent for a uranium source and 6.0 percent for a strontium source.