Bragg peak spectroscopy of low-energy heavy ions

A small ionization chamber with the electric field lines parallel to the particle trajectory (Bragg ionization chamber) allowing the determination of the nuclear charge and the energy of low energetic heavy ions (EA ∼ 0.8–2.0 MeV) is presented together with an adapted shaping amplifier. Using the customary technique of pulse shaping with a long and a short time constant the energy and the Bragg peak resolutions for projectiles between 24He and 1632S were determined. With purified n-pentane an energy resolution of ΔEE = 1.0% and a nuclear charge resolving power of ZΔZ = 47 were measured for 1.5 McV/amu 28Si ions elastically scattered on 197Au. No significant pulse height defect is observable for the energy determination of particles with Z ≦ 17. The Z resolution obtained via Bragg peak measurements was found superior to the Z determination using energy loss measurements which at low energies, in particular, suffer from large uncertainties due to straggling.