Space Charge Sheaths in Positive Ray Analysis

Abstract

It is shown that in the usual ionizing chambers used in the positive ray analysis of secondary ion products a positive ion sheath is formed, which concentrates the field applied across the chamber into the portion of the chamber next to the slit, leaving the rest of the space field-free. A modification of the usual apparatus was used to check this fact. The sheath thickness varies with the voltage applied across the chamber, the electron current, and the pressure, and, inasmuch as some ions are formed best in a field-free space, and some best in a field, by varying any of the three variables, we change the relative proportions of the various secondary and net primary ions reaching the analyser collector. Curves are given for the sheath thickness, and for the various ionic currents through the slit for several conditions in the chamber, and these curves are checked with data given by several observers. This analysis shows the complexity of the phenomenon and indicates modifications in the experimental procedure which may help to clarify the interpretation of experimental results.