High-rate axial-field ionization chamber for particle identification of radioactive beams

Abstract The design, construction and performance characteristics of a simple axial-field ionization chamber suitable for identifying ions in a radioactive beam are presented. Optimized for use with low-energy radioactive beams ( 5 MeV / A ) the detector presents only three 0.5 µm/cm 2 foils to the beam in addition to the detector gas. A fast charge sensitive amplifier (CSA) integrated into the detector design is also described. Coupling this fast CSA to the axial field ionization chamber produces an output pulse with a risetime of 60–70 ns and a fall time of 100 ns, making the detector capable of sustaining a relatively high rate and providing a time resolution of 6–8 ns. Tests with an α source establish the detector energy resolution as ∼ 8 % for an energy deposit of ∼3.5 MeV. The energy resolution with beams of 2.5 and 4.0 MeV/A 39 K ions and the dependence of the energy resolution on beam intensity is measured. At an instantaneous rate of 3×10 5  ions/s the energy resolution has degraded to 14% with a pileup of 12%. The good energy resolution of this detector at rates up to 3×10 5  ions/s makes it an effective tool in the characterization of low-energy radioactive beams.