A method and apparatus for the remote, non-invasive detection or characterization of materials manifests a controlled temperature perturbation to the sample material location concurrently with sample interrogation by ionizing radiation and with detection of the response emission energy spectra. This configuration induces and detects Doppler effects manifested at the sample location, allowing material inventory and composition measurements, and allowing a comparative reduction of the exposure duration compared to other isothermal proportional count, coincidence count or spectral analysis techniques. The method and apparatus apply primarily to the detection of elements and isotopes in baggage handling, cargo inspection, chemical characterization, process control and geologic operations, though the method and apparatus are not restricted to these applications. Though the magnitudes of the measured effects are substance specific, the contributing physical processes are not strictly material dependent, allowing method and apparatus applications to almost any high-energy photon-emitting material in multiple applications.