Properties, Mechanism and Experimental Reduction of Effects of the Time Dependent Field Emission of Photomultiplier Tubes

Abstract

Recently the author advanced the hypothesis that photomultiplier fatigue is caused by the time-dependent accumulation of electric charge at the dynode surface. The corresponding equation contains two exponential terms for an observed double effect characteristic of phototube fatigue and of the Malter effect. A tentative interpretation of this double effect maintains that there are two succesive jumps as the bound electrons of the MgO-Cs dynode escape from the F2 or F2+ centers to the vacuum. Experimental measurements favor the calculations based on the proposed model, although there is no evidence for each particular level. To forestall fatigue effects preventive measures have proven to be insufficient. However, tube gain stabilization can be achieved by a new method in minutes rather than the hours needed previously. Two further methods for correction of distorted energy spectra were developed. Several simple mechanical and electrical devices have been developed for the automatic reduction of fatigue effects by compensation, to as little as 1% of the original values. This holds even in the case of strong sources. Also, methods of suppression of the fatigue phenomenon are discussed. The time dependent field emission equations play an essential role in this study.