A cosmic-ray counter telescope for high mass resolution

A dE/dx by E counter telescope consisting of two ¼-in.-thick plastic scintillators as the dE/dx elements and a 5-in.-deep NaI(Tl) crystal as the E element is described. The geometrical factor of the system is 6 cm2 sr and is energy independent for stopping particles. The calibration of the detector and its response to sea-level muons and the low-energy nuclei of cosmic radiation are presented. The expected mass resolution is compared to that observed, and they are found to be in excellent agreement. Protons, deuterons, 3He, 4He, and heavier nuclei are all resolved over the energy range corresponding to the crystal thickness. Information on the nonlinear behavior of the light output from the plastic scintillator NE102 as a function of ionization loss is presented.