Patent ID: 8779370

Claim:
A method for determining the presence or absence of anomalous radioactive materials in a target in a detection zone, said method comprising: (i) obtaining a target gamma ray spectrum from the target; (ii) preparing, from the target gamma ray spectrum, a target data set comprising a plurality of intensity values, each intensity value being associated with an energy bin representing a gamma ray energy or range of gamma ray energies in the target gamma ray spectrum; (iii) pre-processing the target data set; (iv) performing Principal Component Analysis (PCA) on a correlation matrix of a pre-processed data library so as to generate principal components for a principal component space, wherein the pre-processed data library is obtained by a process comprising obtaining a data library comprising reference gamma ray spectra from Naturally Occurring Radioactive Materials and optionally other anomalous sources; (v) projecting the pre-processed target data set and the pre-processed data library into the principal component space; (vi) determining a distance between the projected pre-processed target data set and one or more clusters of the projected pre-processed data library in the principal component space; and (vii) comparing the distance with a predetermined threshold distance so as to determine if an anomalous radioactive material is present in the target, whereby either: if the distance is greater than or equal to the threshold distance, a signal is generated in response to the presence of the anomalous radioactive material in the target; or if the distance is less than the threshold distance, a signal is generated in response to the absence of the anomalous radioactive material in the target.