Identification of Isotopes of Energetic Particles with Dielectric Track Detectors

This paper describes a new principle of charged-particle identification by plastic track detectors. We find that the rate of chemical etching (by a suitable reagent) along the track of a heavy ion in a plastic depends only on the primary ionization rate, which, as the particle slows down, increases at a rate that depends uniquely on atomic number $Z$ and mass $A$. To identify the $Z$, $A$, and energy of a particle we can either measure the etching rate at a known residual range [by analogy with a $\left(\frac{\mathrm{dE}}{\mathrm{dx}}\right)-E$ detector] or measure the etching rate at two known points along the trajectory in a stack of plastics. We present experimental data for ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{12}$, ${\mathrm{N}}^{14}$, and ${\mathrm{O}}^{16}$ ions from the Yale accelerator, showing that masses differing by 9% can be resolved. Unique features of this method are its discrimination against intense background radiation and its combination of high resolution with large collecting area, which make it feasible to do certain cosmic-ray experiments, such as the detection of ${\mathrm{Be}}^{10}$ nuclei.