Patent Number: 
Section: claims

1. A system, comprising:a generator-detector configured to be attached to a conduit, the generator-detector configured to measure the concentration of mercury in the conduit in a non-destructive manner down to a lower detection limit of 10 ppm±50%. 2. The system as recited in claim 1, wherein the conduit communicates a fluid. 3. The system as recited in claim 2, wherein the conduit is a portion of a pipeline for transporting oil or gas. 4. The system as recited in claim 1, wherein the generator-detector includes a spectroscopic beam generator-detector. 5. The system as recited in claim 4, wherein the generator-detector is configured to measure the concentration of mercury at two locations within the conduit, and wherein the generator-detector is configured to average the two measurements. 6. The system as recited in claim 5, wherein the two locations are about 180 degrees apart from one another. 7. The system as recited in claim 1, wherein the generator-detector uses neutron activation analysis. 8. The system as recited in claim 7, wherein the generator-detector includes a thermal neutron source and a gamma detector. 9. The system as recited in claim 1, further comprising at least one magnet configured to mechanically couple an exterior housing containing the generator-detector to the conduit. 10. The system as recited in claim 9, wherein the generator-detector is configured to project energy to an interior location of the conduit and the at least one magnet are spaced apart from a path of the energy projection. 11. The system as recited in claim 1, wherein the generator-detector is configured to measure mercury in the conduit to a lower detection limit down to 1 ppm±50%. 12. 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). 13. A method, comprising:mechanically coupling a device to an exterior of a conduit;directing at least two neutron beams to at least two target interior locations of the conduit; andmeasuring the concentration of mercury in the conduit using the device in a non-destructive manner by measuring the concentration of mercury at the at least two target interior locations and averaging the at least two measurements. 14. The method as recited in claim 13, wherein the conduit is a subsea pipe, and wherein the device is initially positioned on the subsea pipe by a diver. 15. The method as recited in claim 13, 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. 16. The method as recited in claim 15, wherein the generator-detector is configured to measure mercury in the conduit to a lower detection limit down to at least 10 ppm±50%. 17. The method as recited in claim 16, wherein the generator-detector is configured to measure mercury in the conduit to a lower detection limit down to 1 ppm±50%. 18. The method as recited in claim 13, further including communicating a fluid through the conduit during the coupling, directing, and measuring steps.