Self-absorption effects on alpha-induced atmospheric nitrogen fluorescence yield

Nitrogen fluorescence induced by radiation can be used to detect the presence of radioactive contamination in the environment. Contamination quantification from the fluorescence signal requires: the source’s effective alpha spectrum; the specific radiation quantum fluorescence efficiency; optical attenuation length in air of the fluorescence signal; the absolute throughput and quantum efficiency of the optical instrumentation; calibration of the instrumentation; and radiation transport modeling of the “effective” array exposure rate given the alpha particle spectrum. Field testing conducted on optical instrumentation measured the nitrogen fluorescence yield generated by ²⁴¹Am alpha emissions. Laboratory studies of ²⁴¹Am via alpha spectrometry determined whether the presence of solids on source surfaces produced sufficient self-absorption to decrease fluorescence. Results from the laboratory studies provided correction to the effective alpha-source activity values in a model of the earlier optical-sensor field measurements, and determined the air fluorescence efficiency of alpha particles generated by the ²⁴¹Am sources used in the field experiments.