Improvement of mass resolution for iron isotopes in CR-39 track detector

The capability of the CR-39 track detector for isotope identification was verified using ⁵⁶Fe and ⁵⁵Fe beams from the heavy ion accelerator HIMAC at NIRS. A CR-39 stack was exposed to ⁵⁶Fe and ⁵⁵Fe beams with the energies of 460MeV/nucleon. Drastic improvements in the accuracies of microscopic image analysis and detector thickness measurement enabled us to identify those iron isotopes with high mass resolution using the CR-39 track detector. As a consequence of the reduction of systematic errors, the mass resolution for iron isotopes in the CR-39 detector was obtained to be 0.22 ± 0.03 amu in rms. The mass resolution newly obtained by the CR-39 detector was compared with the former result and found to be 66% better than the former value of mass resolution as a result of reducing the systematic errors of mass dispersion. Moreover, the ultimate mass resolution of the CR-39 detector was estimated by calculation using those experimental results. As a consequence of reducing the random error, it is expected that the mass resolution for iron isotopes can ultimately approach to ∼0.10 amu in the CR-39 detector.