The PERM™ gamma detector uses a 2”x4”x16” NaI(TI) and is designed to achieve ~ 0.5% absolute energy calibration uncertainty and < 0.5% instability. When coupled with PSI’s PCS algorithm, the system provides real-time (1 Hz) isotope ID while operating at a CFAR of < 1 in 340 hrs of continuous 1 Hz sampling in urban and variable R/N environments.