Metal detectors radio frequency detector

The District of Columbia obtained a permit from the National Park Service and the District s staff surveyed this area with a Fisher Gemini-3 Radio Frequency Transmitter-Receiver Metal Detector. They repeated the survey using a Schonstedt GA-72 Cd Magnetic Locator. Thus far, the District has located 13 anomalies that are compatible with munitions burials. Additionally, the EPA s expert in UXO recovery has confirmed the compatibility of several of the District s anomalies with deep munitions burials and has located a 14th anomaly. The anomalies are marked with tape and are plotted on the attached map (deleted for purposes of this book). In addition, the District of Columbia looked at the utility maps to eliminate the possibility that a utility line may account for the anomalies. One such map bears the strange comment, NOTE FOR NONINTERFERENCE BETWEEN NEW CHAIN BRIDGE AND U.R.DC., SEE E.D. 236905-1. ... 

Curie-point pyrolysis involves placing the sample wire into a radio frequency field that induces eddy currents in the ferromagnetic material and causes a temperature rise. When the wire reaches the Curie-point temperature, it becomes paramagnetic and stops inducting power. The temperature at which the wire stabilizes (the Curie point) is a function of the type of metal. For example, the Curie points of cobalt, iron, and nickel are 1128, 770, and 358°C, respectively. Wires made from alloys of these metals produce intermediate temperatures. For example, the commonly used nickel-iron wire has a Curie point of 510°C. Differences between filament and Curie-point pyrolyzers depend on the pyrolysates examined and may be obscured by other instrumental differences, including the design of the transmission system to the detector. 

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