STOPPING POWERS OF GASES FOR HEAVY-IONS (O, AR, KR, XE) AT INTERMEDIATE ENERGY (20-100 MEV/U) - VANISHING OF THE GAS SOLID EFFECT

The stopping powers of eleven gaseous media have been measured for 20-85 MeV/u O, 25-60 MeV/u Ar, 20-40 MeV/u Kr and 25-30 MeV/u Xe ions. The experimental method consists of measuring the energy loss of ions traversing a given thickness of gas contained in a gas cell. The energy measurements are performed using a magnetic spectrometer (LISE). The pressure and temperature of the gases are directly measured by appropriate probes. The stopping powers are thus determined with an accuracy of +/- 2% to +/- 4%. From the comparison of these data with the stopping powers of solids previously measured, the magnitude of the gas-solid effect is estimated. This effect is still observed for 25 MeV/u Xe and vanishes for lighter projectiles at higher energy, when they tend to be fully stripped.