Transfer Efficiency and Storage Capacity of Electronographic Image Tubes.
James B. Breckinridge, Gerald E. Kron, Irakly I. Papiashvili · The Astronomical Journal · 1964
When the highly efficient Ilford nuclear track emulsions are used in electronographic image tubes, as many as five or six submicroscopic grains will be formed per incident electron at 30 kV accelerating potential. A microscopic examination of a plate indicates, however, that the groups of grains formed by each electron fuse into single picture units. These picture units vary widely in size, but the ones that contribute appreciably to the picture are of the order of 1 P in size, and can be seen easily with the aid of an optical microscope. Counts made of these picture units indicate that even for the most efficient of the emulsions, Ilford G5, the conversion efficiency is only 50% for 30 kV electrons; i.e., two electrons are required to form only one appreciable picture unit. We believe that statistically the efficiency of an image tube depends upon this number and not upon the number of grains per electron, and that therefore an image tube, even with G5 emulsion at 30 kV, operates at a loss. The storage capacity of a picture emulsion depends upon the number of picture units that can be stored per unit area before serious saturation sets in. We have made measurements of the storage capacity of Ilford nuclear track emulsions when used in the Lick-Stromlo image tube. We find that because of the small grain size of these emulsions, and because of the high densities that can be used without serious saturation effects, these emulsions have storage capacities of from five to ten times that of Eastman I Ia-O emulsion exposed to light. An image tube used with nuclear track emulsions should therefore be very good for direct "photography," and should make possible the recording of stars and surfaces fainter than heretofore.