Sensitivity measurement of photocathode in insulating capsule - silica tube embedded in capsule as channel for removable test probe

摘要

The photocathode is set at one end of the insulating capsule which is made of silicone rubber and preferably coated externally with silica or perspex; the HT lead serving the photocathode is embedded in a channel which runs the length of the capsule. An electrode serves as a collecting electrode during tests of the sensitivity of the photocathode; it has no function in the normal working of the image tube, but, being near the cathode, it acquires a similarly high potential. This high potential is insulated by use of a contact which connects the test probe to the collecting electrode, situated at the bottom of a second channel, which also runs the length of the capsule and which is lined with a tube of silica or plastic. Between tests the probe is withdrawn, and its channel is plugged with insulating material.