A method for identifying at least one nuclear threat to homeland security, wherein such each nuclear threat is either hidden inside at least one cargo container before transit, or is placed inside at least one cargo container while in transit. Each such nuclear threat while interacting with its surroundings generates a unique nuclear threat signature. The method comprises: (A) detecting at least one nuclear threat signature; (B) measuring a background nuclear threat signature distribution in a nuclear threat-free environment; (C) comparing each detected nuclear threat signature with the background nuclear threat signature distribution; (D) if deviation of the detected nuclear threat signature from the background nuclear threat signature distribution is statistically significant, selecting the detected nuclear threat signature to be a part of an array of statistically significant detected nuclear threat signatures; and (E) substantially continuously processing the array of selected statistically significant detected nuclear threat signatures in order to determine a likelihood of each such nuclear threat.