1. An apparatus for detecting and determining a source azimuth for gamma radiation from a radiation source comprising a set of one or more radioisotopes, the apparatus comprising: a first scintillator detector ensemble comprising at least two scintillation detectors each producing a distinct electrical signal and each comprising a scintillator crystal having a response varying with angular disposition with respect to a source, said crystals being disposed at angular offsets with respect to a reference axis and having an output and a processing and control circuit including a digital processing system configured to analyze spectral data from each electrical signal produced for each crystal, and a processing circuit to evaluate the electrical signals to determine a signal intensity and a likely source azimuth for at least one detected radioisotope in the plane of detection wherein the processing and control circuit is further configured to monitor a finite number of spectral windows corresponding to said set of one or more radioisotopes and compare detected energy spectra to stored signatures.