1. A system for identification of a radiation source, the system comprising: a portable detection unit that detects ionizing radiation from the radiation source and provides a corresponding detection signal, wherein the detected ionizing radiation includes gamma, neutron and X-ray radiation; a multi-channel analyzer, including a microprocessor, that analyzes the detection signal and generates a spectrum of the ionizing radiation; and means for connecting the system to a network and for communicating the spectrum to a remote expert system; wherein, if the microprocessor is unable to unambiguously identify a radioisotope of the radiation source, the system requests information from an expert system at a higher level in a hierarchy, and wherein the hierarchy includes at least two higher levels, including a first expert system located on a local area network, and a second expert system located on a global network.