Stopping energetic heavy-ions in one-bar helium: broad incident momentum distributions

Abstract

Various tests for stopping energetic 32 P fragments in a 50 cm gas cell filled with helium were performed. The fraction of ions stopped in the gas was measured as a function of the width of the incident beam momentum distribution. The use of a shaped degrader placed in a dispersive plane before the gas cell significantly improves the stopping efficiency in gas. A stopping efficiency of 35% was obtained for fragments with the broadest momentum distribution, which was an improvement of approximately 80%. Qualitative agreement between the experimental results and stopping power calculations was obtained.