A stack of twelve NaI (Tl) discs, 2 cm think each, has been exposed to sea level muons, and to beams of relativistic carbon, neon, argon, and manganese at the Berkeley Bevalac. For ^(55)Mn with γ = 2.75, the position-measuring accuracy of individual discs is better than ±2 mm, individual layer responses are close to the Landau distribution, and residual error for measuring total kinetic energy of the stopping ions is less than 0.25%
