Incremental Gains in Transuranic Activity Analysis in Air Samples for Radiological Emergency Response

The alpha activity discrimination problem between radon progeny and transuranic (TRU) isotopes is evaluated at the times relevant for radiological emergency response using temporal decay properties. This study evaluates various effects from naturally occurring radon progeny creating alpha spectral overlap with the TRU region of interest. The methodology helps to address the potential masking of a radiological threat at worst or, at best, inhibiting response efforts due to delays caused by high levels of radon progeny. This work seeks to provide a rapid, conservative TRU estimation method in as little as 30 min. Surrogate TRU activity is introduced to the assays via check sources as a validation test for discrimination against varied levels of radon progeny collected on environmental air samples. A 2-h activity decay profile counting window was sectioned into multiple combinations of 30-min increments to investigate optimal counting segments and to simulate potential field-collection scenarios with limited resource availability. The experiment sought to discriminate low levels of introduced TRU activity comparable to the natural background on each sampled filter. Using this approach, the study confirmed the utility of the estimation methodology in as little as 30 min. Additional measurement time taken in the decay profile demonstrated marked improvements in both accuracy and precision of the TRU activity estimate as expected. Studies on the potential functional dependence of fitting parameters that influence the TRU estimate and associated uncertainty may improve further model development. The methodology is flexible to accommodate any gross alpha/beta scalar counter and is designed to be implemented within a graded approach based on time and resource availability present in the response. The estimation framework enables rapid air assay with a proper technical basis in times not currently realized in radiological emergency response.