RESEARCH ON HIGH GAIN TRANSMISSION SECONDARY EMISSION FILMS.

To achieve a resolution of better than 20 line pairsmm with a low density KCl dynode it seems probable that electric field strengths in excess of 1000 voltscm are required at the dynode exit s in magnetic fields of about 100 gauss. It is not possible to sustain fields of this magnitude with freshly prepared samples of the dynodes currently being fabricated. However, an image tube can be operated with a dynode - grid spacing of 0.25 inches and 1000 volts on the grid to give high resolution provided the dynode be havior has been suitably modified by previous exposure to the vapors in a demountable vacuum system. For a modest fall in gain approximately 20 the dynode breakdown voltage the voltage applied to the grid that just initiates break down can be raised from 150 to 1000 volts in many cases. The exact mechanism of the matur ing process that causes this change is unknown, though in the present case oil contamination probably plays an important part. Author