Final Report: Fiber Optic Sensors With Hydrophilic, Radionuclide-Selective Cladding for the Detection of Radionuclides in Water SuppliesEPA Contract Number: EPD07024
Title: Fiber Optic Sensors With Hydrophilic, Radionuclide-Selective Cladding for the Detection of Radionuclides in Water Supplies
Investigators: Hoyt-Haight, Andrea E
Small Business: Adherent Technologies Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2007 through August 31, 2007
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2007) RFA Text | Recipients Lists
Research Category: SBIR - Homeland Security , Small Business Innovation Research (SBIR)
In this Phase I program, Adherent Technologies, Inc., developed a fiber optic scintillator system with a radionuclide-selective cladding for use in the detection of radionuclide contamination in water supplies or wastewater streams. The current terrorist threat requires that vigilance be maintained on all avenues of attack to the United States, including the potential for attack on the country’s food or water supplies. The major advantage of this technology compared to current off-site laboratory methods of detecting radionuclides in water systems is the “instant” on-site detection, which would allow for an appropriate and timely emergency response.
During this Phase I program, Adherent Technologies, Inc., successfully coated plastic scintillating optical fibers with a hydrogel cladding formulated specifically for chelating radionuclides such as Cesium-137 (137Cs). The hydrogel coatings were highly uniform in thickness and self-equilibrated to a thickness of approximately 70 μm as determined with digital microscopy.
Exposure of these chelating optical fibers to a 137Cs standard solution in conjunction with conventional liquid scintillation counting of the standard solutions before and after exposure showed that the cladding did indeed chelate the radionuclide. A similar non-chelating cladding also was evaluated and did not show any significant pick-up of radionuclide.
These coated fibers were incorporated into a fiber optic sensor configuration by attaching a standard SMA connector to one end of the fiber before the cladding synthesis reactions were conducted.
The Phase I program also involved the construction of a small, lightweight detection system for direct readout of fiber optic sensors. This system consisted of a small photomultiplier tube (PMT) detector equipped with an RS232 data connection, which was placed into a light tight housing that incorporated a shutter and a bulkhead connector for the SMA-connectorized fiber optic sensor. Instrument control and data acquisition were accomplished using a laptop computer and a simple software system supplied by the PMT manufacturer. A small laboratory power supply rounded out the instrumentation system. The complete portable instrument system is shown in Figure 1.
Direct detection of radionuclides in a relatively concentrated standard solution (1 μCi/mL 137Cs) with the aforementioned portable detection system was demonstrated during the Phase I program, although the response level was very low. Several factors probably are involved in this low response, including:
- the thin (~70 μm) chelating coatings; and
- a small exposed area—only about 1 inch of the sensor actually was exposed to the radionuclide solution because of experimental constraints (vessel size and available standard solution).
There are several ways to address these issues including the production of thicker claddings, the use of fiber optic bundles, and adjusting the experimental configuration to allow for immersion of longer lengths of clad optical fibers. The detection system also could be modified to allow multiple connections of sensors to the detector, as the PMT window is very large compared to the actual optical fiber diameters used in these experiments.
Overall, this program was successful in using a portable detection system with a fiber optic sensor to detect one radionuclide that might be incorporated into a radiological “dirty bomb.” Expansion to other radionuclides should be fairly straightforward.
Monitoring of radiological threats to water supplies is similar to the problem of monitoring groundwater contamination at the U.S. Department of Energy (DO E) facilities around the country. Significant challenges include developing a robust detection system that can be used in a continuous monitoring mode and is sensitive to extremely low levels of contamination.
The selective scintillating fiber optic devices that will be developed during this work are expected to be capable of real-time or on-demand analysis and also are amenable to long-term and/or remote monitoring scenarios. When a large volume of scintillator is employed (either as a single fiber sensor or in sensor bundles), these systems also should be capable of providing detection levels corresponding to drinking water standards. In addition, the use of chemically selective preconcentrating layers is expected to further improve the sensitivity and detection limits of the proposed sensor platform. Desirable attributes of these fiber-optic devices include small size, light weight, low cost, low power consumption, and easy integration into a wide variety of application environments. These devices would represent a significant improvement over the current baseline methods that are based on costly laboratory analysis procedures performed at centralized laboratories.
The fiber optic radionuclide detection system that will be developed during this program and its Phase II follow-on can be used to monitor virtually any water source. Perhaps the greatest potential application for this technology is within the 160,000 public water systems around the country, several of which are considered major terrorist targets and are in need of an affordable real-time monitoring system for radionuclide detection. Other sources that may require monitoring include the many streams and lakes that are at risk from mining and industrial concerns, including the massive ongoing waste remediation efforts at DOE facilities around the nation. Additional applications in the medical arena also may be possible.