Charge-state distribution measurements using gas charge stripper toward 238U and 136Xe acceleration at RIKEN RIBF

The charge-state distributions of 238U and 136Xe ions at 11 MeV/nucleon were measured using a gas charge stripper to test whether the charge states in gaseous media were acceptable for acceleration at the RIKEN RI-Beam Factory (RIBF). A differential pumping system facilitated the increase of the N2 gas thickness to 1.3 mg/cm2; this is sufficient for the most probable charge state to attain equilibrium. The charge states of 238U attain equilibrium at 56.0, 56.6, and 55.7 in N2, Ar, and CO2 media with thicknesses of 125, 79, and 126μg/cm2, respectively, whereas those of 136Xe attain equilibrium at 40.5, 40.1, and 40.3 in N2, Ar, CO2 media with thicknesses of 163, 95, and 139μg/cm2, respectively. The equilibrium charge states of 136Xe are acceptable for acceleration by the subsequent cyclotron, whereas those of 238U are not acceptable for acceleration without a major remodeling of the accelerator.