Isotopic identification of energetic heavy nuclei using dE dx vs total energy in a high pressure gas ionization detector

We have developed a high pressure (3-10 atm) segmented-anode gas ionization chamber and have investigated the capabilities of this type of instrument for identifying energetic heavy nuclei. For individual nuclei which stop in the active volume of the detector, we use one or more measurements of the particle's energy loss (ΔE) and its residual energy (E′) to derive its charge and mass. Experiments using accelerator beams have yielded unambiguous charge identification over the range of elements studied (up to Z = 26), and mass resolutions from σ_M {reversed tilde equals} 0.08 amu (Z = 6) to σ_M {reversed tilde equals} 0.35 amu (Z = 26). The energy loss measurements provided by the segmented anode are supplemented by two-dimensional measurements of particle track coordinates made using a combination of drift time and charge division in a set of single-wire proportional counters. These tracking detectors provide a position resolution ≲ 0.6 mm for each coordinate, and make possible the path length corrections needed to study isotropic particle distributions such as those encountered in the cosmic radiation.