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PubMed2001

Extraction of full absorption peaks in airborne gamma-spectrometry by filtering techniques coupled with a study of the derivatives. Comparison with the window method.

In this paper, an adaptation of a spectral profile analysis method, currently used in high-resolution spectrometry, to airborne gamma measurements is presented. A new algorithm has been developed for extraction of full absorption peaks by studying the variations in the spectral profile of data recorded with large-volume NaI detectors (16 l) with a short sampling time (2 s). The use of digital filters, taking into consideration the characteristics of the absorption peaks, significantly reduced the counting fluctuations, making detection possible based on study of the first and second derivatives. The absorption peaks are then obtained by modelling, followed by subtraction of the Compton continuum in the detection window. Compared to the conventional stripping ratio method, spectral profile analysis offers similar performance for the natural radioelements. The 137Cs 1SD detection limit is approximately 1200 Bq/m2 in a natural background of 200 Bq/kg 40K, 33 Bq/kg 238U and 33 Bq/kg 232Th. At low energy the very high continuum leads to detection limits similar to those obtained by the windows method, but the results obtained are more reliable. In the presence of peak overlaps, however, analysis of the spectral profile alone is not sufficient to separate the peaks, and further processing is necessary. Within the framework of environmental monitoring studies, spectral profile analysis is of great interest because it does not require any assumptions about the nature of the nuclides. The calculation of the concentrations from the results obtained is simple and reliable, since only the full absorption contributions are taken into consideration. A quantitative estimate of radioactive anomalies can thus be obtained rapidly.

Air Pollution, Radioactive↗
PubMed1996

Six methods to assess potential radioactive air emissions from a stack.

In accordance with U.S. Title 40, Code of Federal Regulations, Part 61, "National Emission Standards for Hazardous Air Pollutants," Subpart H, U.S. Department of Energy stack emissions which have the potential to cause an exposure > or = 1 muSv y-1 to the offsite maximally exposed individual must meet the continuous monitoring requirements dictated therein. Since February 1993, all 125 stacks operated by the Westinghouse Hanford Company on the U.S. Department of Energy's Hanford Site have been assessed for their potential unabated radionuclide emissions using one of six methods approved for use by the U.S. Environmental Protection Agency, Region 10. These potential emissions combined with the CAP88 code were used to produce dose estimates to the maximally exposed individual. Results show there are 106 stacks in compliance and below the potential to emit greater than the EPA threshold. The 19 remaining stacks will be brought into full compliance under a Federal Facilities Compliance Agreement which was established in February, 1994. While each method maintains the safety and protection of the occupational worker, the public, and the environment, significant cost benefits may be derived by applying the best available technology. The CAP88 code and the methods for estimating potential emissions are presented, as well as the associated results.

Air Pollutants, Radioactive↗