In an event of a radiological dispersion device RDD detonated by terrorists in a high population density area like Atlanta, the hospitals and other medical facilities will be over whelmed by people who may or may not have been contaminated by radioactivity. Under such chaotic circumstances, it would be desirable to separate people who have inhaled radioactive particles from others to direct them immediately for further treatment. Prompt identification of radioactive material would accelerate local authorities response time for protective action. Hence, a portable 3" by 3" NaI detector, which is cheap and widely available at local universities, was utilized to identify and calculate the activity of unknown radioisotopes. The method used was regression analysis and measured responses for radioisotopes behind lucite slabs to simulate various wall thicknesses. An algorithm was developed to identify and calculate activity of unknown isotopes regardless of wall thickness.