A method for discriminating a radioactive anomaly from naturally occurring radioactive materials includes detecting a first number of gamma photons having energies in a first range of energy values within a predetermined period of time and detecting a second number of gamma photons having energies in a second range of energy values within the predetermined period of time. The method further includes determining, in a controller, a ratio of the first number of gamma photons having energies in the first range and the second number of gamma photons having energies in the second range, and determining that a radioactive anomaly is present when the ratio exceeds a threshold value.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
At least a portion of this invention was made with Government support under Cooperative Agreement No. DE-FC52-09NA29293 with the Department of Energy and the National Nuclear Security Administration. The Government may have certain rights in this application.