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. AVIRlS 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.
GammaTracker is a handheld radioisotope identification device in development at Pacific Northwest National
Laboratory that uses eighteen pixelated Cadmium-Zinc Telluride (CZT) crystals to provide energy resolution
approaching that of high-purity germanium without the need for cryogenic cooling. Additionally, these crystals can be
used to provide directional and imaging capabilities that cannot be found in other handheld detectors. A significant
number of CZT crystals have been procured during the development of the GammaTracker system; the majority of these
were procured with the same set of specifications. Each of these detectors has been characterized in terms of key
parameters, including current-voltage response and pixel-by-pixel energy resolution. The results of this testing indicate
that the overall quality of CZT crystals is improving over time.
We present measured data on the neutron detection response of the GammaTracker handheld radioisotope identifier.
Two neutron detection modes are discussed: measuring absorption gamma rays from the cadmium present in the
Te spectrometers, and measuring the absorption gamma rays from moderator material present in the environment. In
both cases, the capture gamma rays can be imaged to help locate a shielded neutron source. In this work, we discuss the
total neutron detection efficiency of the GammaTracker instrument, and we present measured images of shielded neutron
sources. Prospects for gamma-ray rejection are discussed.
We report the results of Differential Aperture X-ray Microscopy (DAXM) measurements near Te precipitates in CdZnTe
grown via low-pressure Bridgman. White-beam Laue patterns were acquired with 3-D spatial resolution (with 0.25 μm
resolution in the scanning directions and 1 μm resolution in depth) at depths of up to 35 μm deep normal to the surface.
We find very little crystal strain (< 10-3) or rotation (<0.05 degrees) near Te precipitates. We also examine local
deformations in the vicinity of a microhardness indent, and find that although significant rotations exist, the spatial
extent is limited to a few tens of microns. Furthermore, observed crystal strains are limited to 5 x 10-3 or less in regions
near the microhardness indent.
Conference Committee Involvement (4)
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIV
13 August 2012 | San Diego, California, United States
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XIII
22 August 2011 | San Diego, California, United States
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XII
2 August 2010 | San Diego, California, United States
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XI
3 August 2009 | San Diego, California, United States