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Technology Factsheet

Portable X-Ray, K-Edge Heavy Metal Detector

Category: Characterization > Monitors > Asbestos Monitoring
Reference # : OST No 134, DOE/EM-0519 Model No : K-Edge

The X-Ray, K-Edge Heavy Metal Detection System consists of three major subsystems: an inspection head, a control rack, and a high voltage & cooling support cart. The X-ray tube and detector module are mounted on a support frame that can be adjusted to accommodate the configuration of the inspected object. The support frame and its attached components is called the inspection head. The control rack includes the computer-controlled data acquisition system and a PC monitor. The high voltage/cooling cart provides power to the X-ray tube and the HPGe (high purity germanium) detector and cooling to the X-ray tube. Inspection Head: The inspection head has been customized for 321-M ventilation duct use. The COMET MXR 160 kV, 3kW, X-ray tube is mounted on one side of the C-frame. A high voltage line and cooling hoses are attached to the X-ray tube. To reduce the radiation output of the X-ray tube, a tungsten collimator and copper filter are permanently mounted on the beam's output for this demonstration. Additional collimators and filters are installed as necessary to further reduce the X-ray tube's radiation output. Opposite the X-ray tube and mounted on the other side of the C-frame is the imaging unit and the HPGe detector. These components can be laterally shifted to bring them in line with the X-ray tube. The imaging unit is a phosphor screen, in a light-tight box, viewed by an intensified CCD camera, interfaced to the control rack computer through a frame-grabber board.The HPGe detector is an EG&G ORTEC model GLP-16HCR-S detector. Power, signal, and control cables link this side of the C-frame to the control rack and the high voltage (HV) cart. The HPGe detector cryostat is filled with liquid nitrogen to cool the germanium crystal to its operating temperature. The weight of the inspection head is 120 pounds (lbs). In the inspection head's "closed" configuration, the opening for a container is 24 inches: In the inspection head's "expanded" mode, the opening is 36 inches. For the demonstration, the inspection head was attached to a vertical stand. The vertical stand, mounted on a dolly, was used to position the inspection head around the exhaust ducts. The vertical stand was moved over scaffolding platforms to get the inspection head close enough to the exhaust ducts to perform holdup measurements. A wood mock-up of the inspection head was used to facilitate interference identification and determine scaffolding needs. Control Rack: The control rack is where the operator sat during the duration of the demonstration. A personal computer (PC) monitor on the control rack provided a real-time graph of photon counts versus X-ray energy. This display showed the K-edge drop, which could be correlated to a heavy metal concentration. The control rack could be up to 80 feet away from the inspection head (limited by signal and control cables). High Voltage / Cooling Cart: The high voltage unit and the cooling system rest on a moveable platform. The high voltage unit requires a 230 volt power supply. It transformed 230 volts into 160 kilovolts and supplied this high voltage/low current power to the X-ray tube. The cooling system used a Haskris water-to-air cooler. The cooling system provided constant cooling to the X-ray tube. The length of the cooling hose and the length of the high voltage power supply line required the HV/cooling cart to be within 60 feet of the inspection head. A safety interlock system was set up to assure that personnel were not inadvertently exposed to excess radiation. Dimensions of Tech Model (LxWxH): Weight of Tech Model (lb):

Benefits

-Provides a precise assay measurement -Provides a quantifiable profile of the heavy metal holdup within a container -Provides a real-time record of each image and narrow beam spectroscopic measurement -Provides a non-destructive evaluation of containers with different geometries and with varying wall thicknesses. -Assay system capable of measuring amount of hazardous and nonradioactive elements inside a sealed structure. -Improves worker safety during dismantlement by quantifying heavy metals and radionuclides inside sealed process equipment.

Limitations

The size and weight of the inspection head was the most limiting feature of the X-ray, K-edge technology. Lighter and smaller detector technologies are currently being investigated. It was not feasible to make spectroscopic measurements at every point where the X-ray image indicated the presence of uranium. To obtain the total amount of uranium holdup in a region, a calibration was performed to relate the image density (in gray scale units ranging from 0 to 255) to uranium density (in mg/cm 2 ). Then it was possible to sum up, pixel by pixel, the total amount of uranium in a region. Each image covered a 12cm by 12cm region of the duct (approximately a 5-inch square). Refinements to a recently developed computer program will make the gray scale to uranium density correlation more accurate.

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