Gas Ionization Chamber for Particle Identification at RIBLL

A longitudinal field twin-fold ionization chamber (607mm×490mm×144mm) with an active area 410mm×100mm for particle identification at the Radioactive Ion Beam Line in Lanzhou (RIBLL) was described. It has a configuration of one common cathode and double position sensitive anodes with grounding Frish grids. The entrance and exit windows as well as cathode and anodes were all made of 4μm thick mylar foils. The cathode was coated with 1.5μm silver on both sides and the anodes were deposited with 13 and 3 silver strips (31.5mm width and 0.5mm interstrip gap) in vertical and horizontal directions respectively. The plateau curves of the pulse height dependence on the cathode and anode voltages and the energy resolution Δ E/E for a working gas P10(10%CH 4+90%Ar) were measured with an α source. In the case of gas pressure 250 mbar, cathode voltage-1600V and anode voltage 220V, an energy resolution of 4.7% was achieved.