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Tech ID: 78
Project Overview
The scope of this TTP includes a variety of techniques to exploit
laser-induced fluorescence (LIF) in several environmental applications,
including aerial remote sensing and hand-held portable survey tools
for detecting uranium on surfaces and subsurface contaminants via
vegetation stress. This task has required the development of hardware,
software, and analysis methods for ground-based and airborne laser-induced
fluorescence imaging (LIFI) systems. The current LIFI configurations include
UV and visible laser source (355 nm and 532 nm wavelength),
intensified Charged-Coupled Device (CCD) cameras, and video monitors for
instantaneous viewing. Video images can also be electronically stored for
further analysis and display. This years scope of work includes 1) the
completion of customer requested upgrades and fielding of the portable
uranium survey tool at DOE sites for characterizing facility walls, floors,
equipment, and surface soils; and 2) the completion and flight testing
of the airborne LIFI system. The hand-held uranium survey tool will be fielded
in cooperation with EM-40 personnel for D&D applications at the Oak Ridge
Facility (K-25) and the Fernald Facility. It will also be deployed at EPCOT
Center's Land Pavilion to collect data on plant stress. The airborne LIFI
system was configured for the DOE Convair 580T aircraft. The system has been
reconfigured for helicopter usage, so that deployment is now possible on a
variety of platforms, including the U-60 class (Blackhawk, Seahawk, Pavehawk),
Chinooks, and SH-3s.
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Technology Description
LIF is an optical technique that exploits the detection of fluorescent compounds
irradiated with laser light or filtered conventional light sources. Fluorescence
is the prompt luminescence of a material caused by an external stimulus -
in this case, a laser. When the stimulus ceases, so does the fluorescence. Common
compounds which fluorescence include such organics as chlorophyll in plants and
hydrocarbon fuels. When uranium is excited by a UV laser, however, its peak
fluorescence is persistent (phosphorescent), lasting well longer than the laser
pulse. Operationally, the prompt fluorescence of compounds which may mask the
presence of uranium can be removed by delaying the activation of a photon detector
60 nsec after a laser pulse. This precise delay ensures the extinction of
prompt fluorescence, effectively isolating the presence of uranium. |
