Experimental and mathematical determination of the image plane in a spark source mass spectrograph

An experimental method involving precise measurements of the line displacements versus accelerating voltage was developed for checking the photoplate position in a spark source mass spectrograph. Data obtained from a set of identical exposures recorded using a damped discharge mode result in curves whose shape is related to the relative position of the collecting plate and of the image plane. These experiments are in good agreement with a geometrical calculation taking into account the fringing fields of the magnetic sector. (Auth.)