Engineering topics
Stewart, Trevor N.
Publications and source records attributed to Stewart, Trevor N..
Lead Slowing Down Spectrometry Analysis of Data from Measurements on Nuclear Fuel
Improved non-destructive assay of isotopic masses in used nuclear fuel would be valuable for nuclear safeguards operations associated with the transport, storage and reprocessing of used nuclear fuel. Our collaboration is examining the feasibility of using lead slowing down spectrometry techniques to assay the isotopic fissile masses in used nuclear fuel assemblies. We present the application of our analysis algorithms on measurements conducted with a lead spectrometer. The measurements involved a single fresh fuel pin and discrete 239Pu and 235U samples. We are able to describe the isotopic fissile masses with root mean square errors over seven different configurations to 6.35% for 239Pu and 2.7% for 235U over seven different configurations. Funding Source(s):
Simulations of Material-Dependent Detector Responses for Airborne Gamma-Ray Spectroscopy
The aim of this work is to create a library of predicted detector responses used for real-time background estimation during airborne gamma-ray spectroscopy. The simulated spectra are a function of naturally occurring radioactive potassium, uranium, and thorium (KUT) and radioactive daughter products which are present in terrestrial-based materials. Self-attenuation within these materials varies, such that the gamma spectra emitted from the surfaces can differ, despite all having KUT origins. This study also compared various simulated detector responses among materials to determine if some could be accurately scaled from another across reasonable helicopter altitudes and orientations, relative to the ground. Results show that materials with comparable sample thicknesses can be scaled consistently across altitude. This work allows for efficient background estimation via aggregation of simulated detector responses in real time.
Estimating radiological background using imaging spectroscopy
Optical imaging spectroscopy is investigated as a method to estimate radiological background by spectral identification of soils, sediments, rocks, minerals and building materials derived from natural materials and assigning tabulated radiological emission values to these materials. Radiological airborne surveys are undertaken by local, state and federal agencies to identify the presence of radiological materials out of regulatory compliance. Detection performance in such surveys is determined by (among other factors) the uncertainty in the radiation background; increased knowledge of the expected radiation background will improve the ability to detect low-activity radiological materials. Radiological background due to naturally occurring radiological materials (NORM) can be estimated by reference to previous survey results, use of global 40K, 238U, and 232Th (KUT) values, reference to existing USGS radiation background maps, or by a moving average of the data as it is acquired. Each of these methods has its drawbacks: previous survey results may not include recent changes, the global average provides only a zero-order estimate, the USGS background radiation map resolutions are coarse and are accurate only to 1 km – 25 km sampling intervals depending on locale, and a moving average may essentially low pass filter the data to obscure small changes in radiation counts. Imaging spectroscopy from airborne or spaceborne platforms can offer higher resolution identification of materials and background, as well as provide imaging context information. AVIRIS hyperspectral image data is analyzed using commercial exploitation software to determine the usefulness of imaging spectroscopy to identify qualitative radiological background emissions when compared to airborne radiological survey data.