The response of an isobutane filled ion chamber to heavy ions

A gridded ion chamber with its anode split to record both total energy and rate of energy loss has been used with isobutane gas to detect ions of seventeen elements (17 <= Z1 <= 92) in the velocity range 2 < (137upsilon/c) < 6. The rate of energy loss and the ionisation collection efficiency were found to be independent of pressure over the range 15-50 Torr. The effective charge of the ion moving in the gas is observed to oscillate with Z1. This variation and its effect on the resolution of the rate of energy loss signal are discussed. The effective charge of the moving ion in the ion chamber window (solid polypropylene) does not oscillate with Z1 but probably depends on the ion charge before entering the window. (orig.)