Patent Number: 
Section: claims

1. A system, comprising:a generator-detector including an exterior housing configured to be attached to a pipe, the generator-detector including a spectroscopic beam generator-detector provided within the exterior housing and configured to measure the concentration of mercury in the pipe in a non-destructive manner. 2. The system as recited in claim 1, wherein the pipe is a portion of a pipeline for transporting oil or gas. 3. The system as recited in claim 2, wherein the pipe is a portion of a subsea pipeline. 4. The system as recited in claim 1, further comprising at least one magnet in direct contact with the exterior housing and the pipe such that the at least one magnet is configured to mechanically couple the exterior housing to the pipe. 5. The system as recited in claim 1, wherein the generator-detector is configured to measure mercury in the pipe down to a lower detection limit of 10 mg/kg±30%. 6. The system as recited in claim 1, wherein the generator-detector is configured to measure mercury in the pipe to a lower detection limit down to at least 10 ppm±50%. 7. The system as recited in claim 6, wherein the generator-detector is configured to measure mercury in the pipe to a lower detection limit down to 1 ppm±50%. 8. The system as recited in claim 1, wherein the generator-detector is configured for use underwater at a depth down to at least 75 meters (about 250 feet). 9. The system as recited in claim 1, wherein:the exterior housing is connected to an underwater pipe adjacent a seafloor, andthe generator-detector is connected by a tether to a controller and a power source of a remotely operated vehicle adjacent a water line. 10. The system as recited in claim 1, wherein generator-detector is configured to measure the concentration of mercury in the pipe at a location where the mercury is circumferentially bound by a wall of the pipe. 11. A system, comprising:a generator-detector configured to be attached to a pipe, the generator-detector configured to measure the concentration of mercury in the pipe in a non-destructive manner, andwherein the generator-detector is configured to measure the concentration of mercury at two locations within the pipe, and wherein the generator-detector is configured to average the two measurements. 12. The system as recited in claim 11, wherein the two locations are about 180 degrees apart from one another. 13. The system as recited in claim 11, wherein the generator-detector uses neutron activation analysis. 14. The system as recited in claim 13, wherein the generator-detector includes a thermal neutron source and a gamma detector. 15. A method, comprising:mechanically coupling a device to a pipe; andmeasuring the concentration of mercury in the pipe using the device in a non-destructive manner to a lower detection limit of 1 ppm±50%. 16. The method as recited in claim 15, wherein the pipe is a subsea pipe, and wherein the device is initially positioned on the pipe by a diver. 17. The method as recited in claim 15, wherein the device includes a generator detector and the generator-detector includes at least one of a spectroscopic beam generator-detector, a thermal neutron source, and a gamma detector. 18. The method as recited in claim 15, wherein the step of mechanically coupling the device to the pipe includes using a magnet to mechanically couple the device to the pipe, the magnet directly contacting the pipe and an exterior housing of the device. 19. The method as recited in claim 15, wherein:the step of measuring the concentration of mercury in the pipe includes measuring the concentration of mercury at two locations within the pipe and averaging the two measurements, andthe two locations are about 180 degrees apart from one another.