A method, logic and system are provided for generating data representing all possible materials that may be present when monitoring a region or space for a radioisotope of interest. All possible materials with which a radioisotope material may interact are grouped or categorized into one of a plurality of material groups. Each material group is further subdivided into a plurality of subgroups based on atomic number of a material. First data is stored for each of the subgroups of each of the plurality of material groups, where the first data represents an interaction between a representative material for a corresponding subgroup and radiation at a plurality of energy levels. Second data is stored representing spectral characteristics of each radioisotope of interest at the plurality of energy levels. For a radioisotope of interest, a computation is made to produce spectrum data resulting from an interaction between of the radioisotope of interest using the second data with the first data for each of the plurality of subgroups in each material group. The spectrum data is then stored in a library for later use in the field with the output from a detector. Spectrum data is stored for the particular detector to be used in the field, and to this end, such detector-specific spectrum library data may be adjusted to account for a detector's quantum efficiency and resolution characteristics.