A new gamma detector for fast coincidence measurements with a good energy resolution

Abstract

This chapter provides an overview of the transmission secondary emission image intensifier tube. Electrons from a tri-alkali photocathode are accelerated and focused on to a series of dynodes where multiplication takes place by transmission secondary emission. The electrons from the final dynode are then focused on to the output phosphor. The body is formed from a number of equally spaced metal rings joined together by short glass cylinders. Some of the rings serve as supports for the multiplying dynodes, whilst, the intermediate electrodes are attached to others. Focusing is achieved by superimposed uniform electric and magnetic fields, and a field of 260 G is required with an overall potential of 34 kV. Each multiplying dynode consists of layers of aluminum and potassium chloride on a thin supporting film of aluminum oxide. From a single film an electron gain of about 6 at an accelerating potential of 4.2 kV is typical. The phosphor used at present is silver-activated zinc sulfide P.11, however there should be little difficulty in replacing this with the faster P.16 if required. Resolutions of 23 lp/mm have been obtained in experimental tubes with photocathodes and output phosphors 45 mm in diameter.