Year
2010
Abstract
The purpose of this project is to establish a correlation between prevailing weather conditions and background gamma radiation levels at radiation portal monitors deployed at various ports worldwide, and to devise a mechanism by which the effects of these weather-induced background fluctuations could be mitigated. The task of detecting special nuclear material (SNM) by passive gamma spectroscopy is very much akin to finding a needle in a haystack in terms of the signal-to-noise ratio observed in an uncontrolled environment. Due to their low activities and the low energies of their characteristic gamma rays, the signals from many types of SNM can easily be obscured or drowned out entirely by background radiation. While this can be somewhat mitigated by taking regular background radiation measurements, even this cannot resolve the issue if background levels change suddenly and dramatically. Existing research suggests that the advent of precipitation is the culprit behind many such large and sudden increases in background radiation. The correlation between weather and background levels will be explored by in-situ testing on a full-scale portal monitor at Oak Ridge National Laboratory, and by comparing previously recorded background radiation and weather data from portal monitors located at ports worldwide. The first will be utilized to determine the mechanism(s) by which precipitation introduces background radiation, and the second shall be used to quantify the effects of various quantities and types of precipitation in various parts of the world. Once this analysis is complete, a method of mitigating these changes in background radiation will be developed based on the collected data.