This paper investigates the use of a suitable gamma detector array to increase the detectably of explosives in a prompt-gammas neutron activation analysis (PGNAA) system. Monte Carlo simulations (MCNP-4C) were used for analyzing the system. It was found that the system's performance is enhanced by the use of four detectors: three of the are located on the same side as the neutron source and the fourth on the opposite side. Signature-based radiation-scanning, with nine signatures for each detector, is also discussed.