Degree of ionization in antiprotonic noble gases

The ionization of antiprotonic noble-gas atoms due to formation and Auger deexcitation was investigated. The experiment was performed at low target pressures (p\ensuremath{\le}50 hPa) in order to prevent electron refilling from neighboring atoms. For this reason, the cyclotron trap was used. This device is designed to stop as many particles as possible in a small stop volume at even low gas pressure. The degree of ionization was determined in antiprotonic neon, argon, and krypton by means of measuring yields of circular radiative transitions at relatively high principal quantum numbers. X rays were observed between 1.6 and 21.0 keV using a Si(Li) detector. Complete ionization was found in all three cases.