SBIR-STTR Award

Contamination from mercury and other heavy metals in the environment can present a health risk to both humans and wildlife. Sources of these contaminants can be difficult to locate, especially if lost beneath the surface of old building materials and legacy equipment. This work will develop a portable imaging spectrometer for non-intrusive detection and localization of mercury hotspots. Depending on the material type, a penetrating neutron or photon source of radiation will be used to stimulate nuclear and atomic transitions within the contaminant, causing it to emit identifiable photon signatures that are detected by the sensor. With enough collected data, the direction of the contaminant can also be resolved. Phase I of this project will investigate the sensitivity of these pixelated, cadmium-zinc-telluride-based sensors to mercury contamination. A series of simulations and experiments will be conducted to quantify the time needed to detect a significant quantity of mercury. The results will determine whether the sensitivity of these instruments is useful for mercury remediation, and furthermore, if the device has commercial potential. Following a successful first project phase, the instruments will be optimized to enhance sensitivity. There are hundreds of superfund sites around the country with lead or mercury listed as primary contaminants, presenting a vast opportunity for cleanup guided by this sensor. Due to its penetrating signal and potential for sampling wider areas, this device is capable of reaching locations that are, so far, uncharacterized. This could lead to the discovery of hidden contaminants to initiate their removal, to the benefit of local wildlife and surrounding communities. Characterization of other contaminants and materials using this device will also be explored after the first phase. The two complementary methods for signal production and analysis that are paired with this sensor, called K-x-ray fluorescence and prompt gamma neutron activation analysis, have been used by environmental scientists, archaeologists, geochemists, and other researchers for decades. By providing signal directionality in a portable package, these sensors have the potential to change the way these scientists take their measurements.

Contamination from mercury and other heavy metals can present a health risk to humans and wildlife. Sources of these contaminants can be difficult to locate, especially if lost beneath the surface of building materials and equipment where mercury was used. This work will develop a portable imaging spectrometer for non-intrusive detection and localization of mercury globules trapped beneath the surface of materials. A penetrating neutron radiation source will be used to stimulate nuclear and atomic transitions within the mercury, causing it to emit identifiable and penetrating photon signatures that are detected by a pixelated CdZnTe sensor. With enough collected data, the direction of the contaminant can also be resolved via Compton imaging. Phase I investigated the feasibility of using prompt gamma activation analysis for mercury detection in building materials using Monte Carlo simulation validated by measurement. A CdZnTe detector was chosen for the study because of its portability, good energy resolution, and imaging capabilities. A measurement of mercury within a 2-in steel pipe was recorded, and the data was used to calculate detection limits for various sizes of mercury globules. For the spectrometer used in this work, which contained 19 cm3 CdZnTe, a globule the size of a quarter dollar could be detected within about 30 minutes. This result is in rough agreement with Monte Carlo simulation. Imaging of the neutron-capture gamma from mercury was also experimentally demonstrated, but an improved background subtraction algorithm is needed for imaging outside the lab. The results from Phase I show that mercury detection is feasible for steel objects containing globules of mercury, and work continues for other building materials, equipment, and other pipe sizes.The goal of this Phase-II effort is to develop, build, and test a prototype imaging spectrometer for active interrogation of mercury and other materials. The unit will be hand portable and contain about six times the volume of CdZnTe compared to the detector used during Phase-I, which could improve detection limits by more than a factor of five. A 9-MeV-dynamic-range analog readout chip will be used in the system, allowing for measurement of the entire spectrum of neutron-activation gammas from mercury and other materials. Research and development of new algorithms for neutron activation analysis including isotope identification, multi-MeV gamma imaging, and three-dimensional imaging will also be developed. The final prototype will be tested using a neutron source and activated materials to verify performance. The project will deliver a handheld prototype system for detection and imaging of neutron-activated mercury and other materials.The high-efficiency and high-dynamic range imaging spectrometer proposed for development will also be sensitive to chemicals, explosives, and other contraband of interest for national security and military applications. Other applications of the instrument include range verification for proton beam therapy, detection of chlorine intrusion in roadways and bridges to improve US transportation infrastructure, and vehicle-mounted sensors for large-area mapping of gamma rays. The detection and imaging algorithms developed under this program will advance the state of the art in portable gamma spectrometers by improving spectroscopic and imaging performance of CdZnTe detectors for gammas >3 MeV.