Arthur J. Dempster: North America's First Mass Spectroscopist

摘要

Dempster first ventured into 'positive ray analysis' during his doctoral research in which he studied the properties of slow canal rays' (positive ions) using a positive ray analyzer patterned exactly after that described by Thomson. The most popular method of ionization was by gas discharge which produced energetic ions with a wide range of high velocities. Dempster chose instead to ionize gases by electrons emitted from a Wehnelt cathode, and wsa thus able to produce ions whose velocity he could control. Further, he was able to vary the pressure of the gases under investigation while still maintaining ionization of the gas.