A study of electron impact ionization, x-ray photoionization, and x-ray photoemission currents in silicon diode array camera tubes

When the target of a camera tube is biased sufficiently negative with respect to the cathode that the primary-electron beam is prevented from striking the target, the current collected by the target has three major components: one due to electron impact ionization of the residual gas, one due to soft x-ray photoionization of the residual gas, and one due to photoelectron emission from the target by soft x-rays. The effects of tube pressure and electrostatic potentials on the various components of target current were investigated. The soft x-rays generated by the electron beam striking the mesh are shown to be a significant factor in determining the target current. The study has resulted in a technique for determining the residual gas pressure in a completed camera tube.