A device is described which makes possible the determination of the energy spectrum of protons, alpha particles, or deuterons in the presence of other charged particles. Energy loss per unit path length (dE/dx) and total energy (E) are displayed in the form of voltage pulses of varying amplitudes in quadrature on an oscilloscope screen. The peaks of the pulses are intensitifed, resulting in hyperbolic loci for different types of particles. By masking the oscilloscope screen and using the moving film pulse height analysis technique developed in this laboratory, independent energy spectra may be obtained for each type of particle.