High-resolution real-time optical studies of radiological air sample filtration processes in an environmental continuous air monitor

The need for a continuous air monitor capable of quick and accurate measurements of airborne radioactivity in close proximity to the work environment during waste management, site restoration, and D&D operations led to the Los Alamos National Laboratory development of an environmental continuous air monitor (ECAM). Monitoring the hostile work environment of waste recovery, for example, presents unique challenges for detector design for detectors previously used for the clean room conditions of the typical plutonium laboratory. The environmental and atmospheric conditions (dust, high wind, etc) influence aerosol particle penetration into the ECAM sampling head as well as the build-up of deposits on the ECAM filter. Dust deposits cause complex microstructures to form, onto which incoming plutonium bearing aerosols deposit. This leads to potential degradation in alpha spectroscopy used to detect the relatively few aerosol particles that would be expected to be collected in the early temporal stages of a significant airborne plutonium release incident. From the worker protection perspective, it is the early detection performance that counts, not the ability to ultimately determine the true average concentration during a release episode. Average concentration can be measured more accurately using simple high volume air sampler for collection and retrospective laboratory analysis of the filters. For realistic studies of particulate deposit structure formation on ECAM filters and their impact on alpha spectroscopy, a modified ECAM sampling head equipped with optical microscopy system feeding data to a high resolution video data capture and logging instrument was constructed. The combination of the internally focused microscope with the high-resolution digital camera and image analysis software allows for digital recording and analysis of the filter surface in near real time as aerosol structures evolve during sampling. The mounting of the optical system in the ECAM, in the same geometry as the radiation detector, is critical for realistic aerosol particle penetration and deposition analysis. Collection of alpha spectra using a second ECAM provides data for parallel assessment of the influence of microstructural features of the filter surface deposits simultaneously with the degradation of the ability of the ECAM system to distinguish isotopes based on their alpha energy. Different types of particulate and atmospheric influences will be brought to bear on determining ECAM operational parameters and selection of filter media that will compensate for the deleterious effects of aerosol microstructure formations during monitoring under adverse conditions.