Photomultiplier Transit-Time Measurements

Electron transit time has been measured as a function of over-all voltage, and of the position illuminated on the photocathode, for the following photomultipliers: 931-A, 5819, 6342, 6199, 6292. In addition, a few preliminary measurements have been made for the new RCA 6810 and a new Westinghouse transmission-type tube. Light pulses from a spark gap simultaneously illuminated a 935 phototube and, through attenuators, small areas on the various multiplier photocathodes. The two output pulses were displayed on the same cathode-ray tube sweep, recorded photographically, and their time difference measured by reference to a superposed 700-mc sine wave. As a function of voltage, the 5819, 6342, and 6199 transit times range between 21 and 38 mysec, and fall on a single curve as expected from their similar geometries. The 931-A shows values between 11 and 18m¿sec, the 6292, 56-73 musec, and the Westinghouse transmission type of the order of 3 m¿sec. As a small illuminated spot is moved across the photocathode, transit-time variations range from 3m¿sec for the 5819 to 8m¿sec for the 6292.