1. A method for identifying at least one nuclear threat to homeland security; each said nuclear threat either being hidden inside at least one cargo container before transit, or being placed inside at least one cargo container while in transit; each said nuclear threat while interacting with its surroundings generates a unique nuclear threat signature; said method comprising: (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 said detected nuclear threat signature with said background nuclear threat signature distribution; (D) if deviation of one or more of said detected nuclear threat signatures from said background nuclear threat signature distribution is statistically significant, selecting said one or more detected nuclear threat signatures to be a part of an array of statistically significant detected nuclear threat signatures; and (E) substantially continuously processing said array of selected statistically significant detected nuclear threat signatures in order to determine a likelihood of each said nuclear threat.