A long-range method and a system for reliably detecting and identifying special nuclear materials is provided that relies on the emission of delayed neutrons present in the decay of fission products (delayed neutron precursors) as a unique signature for the special nuclear materials, such as highly enriched uranium (.sup.235/238U). The method relies on a time-of-flight measurement in the first 1 .mu.s after the inducing radiation pulse, and pulse height data analysis for both neutrons and gamma rays that can be done at a much higher data rate than in traditional pulse processing systems. The thermal neutron fission within the time regime of 100-500 .mu.s provides a unique signature of special nuclear materials such as the highly enriched uranium.
STATEMENT OF GOVERNMENT LICENSE RIGHTS
 The present invention was made with Government support under contract number DE-AC02-98CH10886, awarded by the U.S. Department of Energy, and contract number IACRO 09-46641 by the U.S. Department of Defense. The government has certain rights in the invention.