Patent Number: 058964290
Section: claims

1. A method for inspecting a carbon hearth-wall liner inside a metal jacket of a furnace from outside the furnace, the carbon hearth-wall liner adapted to contain molten metal, comprising the following steps: directing photons of radiation into the hearth-wall liner;  directing neutrons into the hearth-wall liner;  measuring radiation emitted from the hearth-wall liner as a result of having directed the photons and the neutrons into the hearth-wall liner; and  analyzing the measurements to determine the remaining thickness of the hearth-wall liner and the extent to which the molten metal has infiltrated the hearth-wall liner.  directing photons of gamma radiation into the hearth-wall liner;  using at least one radiation detector to measure radiation backscattered out of the hearth-wall liner and to measure gamma radiation produced as a result of pair production by the gamma radiation directed into the hearth-wall liner; and  comparing the amount of backscattered radiation to the amount of radiation directed into the hearth-wall liner to estimate the thickness of the hearth-wall liner.  directing neutrons into the hearth-wall liner;  using a radiation detector to monitor for gamma radiation produced when the neutrons are absorbed;  measuring the time elapsed between the neutrons being directed into the hearth-wall liner and the production of the gamma radiation; and  using the measurements of elapsed time to estimate the amount of metal in the volume of the hearth-wall liner.  directing electromagnetic radiation into the wall;  directing neutrons into the wall; and  measuring and analyzing radiation emitted from the wall as a result of having directed the electromagnetic radiation and the neutrons into the wall to evaluate the remaining thickness of the wall and to determine the extent to which the wall has been infiltrated by another material.  a photon generator for generating photons of gamma radiation that are directed into the hearth-wall liner;  a neutron generator for directing neutrons into the hearth-wall liner;  at least one detector for detecting and measuring photons of radiation emitted from the hearth-wall liner as a result of having directed the radiation and the neutrons into the hearth-wall liner; and  a computer for analyzing the measurements to determine the remaining thickness of the hearth-wall liner and the extent to which the molten metal has infiltrated the hearth-wall liner. 2. The method of claim 1, wherein the photons directed into the hearth-wall liner have an energy greater than a pair production threshold of 1.02 MeV. 3. The method of claim 2, wherein the radiation is emitted in photons and the analysis of the measurements further includes evaluating the number of photons emitted with an energy of approximately 511 keV. 4. The method of claim 2, wherein the radiation is emitted in photons and the analysis of the measurements further includes evaluating the number of photons emitted with an energy in a range between about 200 keV and about 511 keV. 5. The method of claim 2, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors and the determination of the remaining thickness of the hearth-wall liner further includes comparing the amount of radiation measured in each of the detectors. 6. The method of claim 2, wherein an electron accelerator triggers the emission of neutrons directed into the hearth-wall liner. 7. The method of claim 2, wherein the analysis of the measurements includes comparing the measurements with values predicted using a simulation program. 8. The method of claim 7, wherein the photons directed into the hearth-wall liner include bremsstrahlung radiation produced by an electron accelerator. 9. The method of claim 8, wherein the bremsstrahlung radiation has an energy of 3 to 8 MeV. 10. The method of claim 1, wherein the analysis of the measurements includes evaluating, as a function of time, emission of radiation produced by neutron absorption. 11. The method of claim 1, wherein the analysis of the measurements includes comparing the measurements with values predicted using a simulation program. 12. The method of claim 1, wherein the molten metal is iron. 13. A method for inspecting a carbon hearth-wall liner of a furnace from outside the furnace, the carbon hearth-wall liner containing molten metal, comprising the following steps: 14. The method of claim 13, wherein the gamma radiation directed into the hearth-wall liner has an energy greater than the pair production threshold of 1.02 MeV. 15. The method of claim 14, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors and the determination of the remaining thickness of the hearth-wall liner further includes comparing the amount of radiation measured in each of the detectors. 16. The method of claim 14, further including the step of comparing the measurements from the radiation detector to values predicted using a simulation program. 17. The method of claim 16, wherein the photons directed into the hearth-wall liner include bremsstrahlung radiation having an energy of 3 to 8 MeV. 18. The method of claim 13, wherein the metal is iron. 19. A method for inspecting a carbon hearth-wall liner of a furnace from outside the furnace, the carbon hearth-wall liner adapted to contain molten metal, comprising the following steps: 20. The method of claim 19, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors and the determination of the remaining thickness of the hearth-wall liner further includes comparing the amount of radiation measured in each of the detectors. 21. The method of claim 19, further including the step of comparing the measurements from the radiation detector to values predicted using a simulation program. 22. The method of claim 19, wherein the metal is iron. 23. A method for inspecting a wall comprising the following steps: 24. The method of claim 23, wherein the electromagnetic radiation directed into the wall has an energy greater than a pair production threshold of 1.02 MeV. 25. The method of claim 24, wherein the radiation is emitted in gamma-ray photons and the analysis of the emitted-radiation measurements further includes evaluating the number of photons emitted having an energy of approximately 511 keV. 26. The method of claim 24, wherein the radiation is emitted in photons and the analysis of the measurements further includes evaluating the number of photons emitted with an energy in a range between about 200 keV and about 511 keV. 27. The method of claim 24, wherein the radiation emitted from the wall is detected by a plurality of detectors and the determination of the remaining thickness of the wall further includes comparing the amount of radiation measured in each of the detectors. 28. The method of claim 24, wherein an electron accelerator triggers the emission of neutrons directed into the wall. 29. The method of claim 24, wherein the analysis of the emitted-radiation measurements includes comparing the emitted-radiation measurements with values predicted using a simulation program. 30. The method of claim 29, wherein the photons directed into the wall include bremsstrahlung radiation produced by an electron accelerator. 31. The method of claim 30, wherein the bremsstrahlung radiation has an energy of 3 to 8 MeV. 32. The method of claim 23, wherein the analysis of the emitted-radiation measurements includes evaluating, as a function of time, emission of gamma rays produced by neutron absorption. 33. The method of claim 32, wherein the analysis of the emitted-radiation measurements includes comparing the emitted-radiation measurements with values predicted using a simulation program. 34. An apparatus for inspecting a carbon hearth-wall liner inside a metal jacket of a furnace from outside the furnace, the carbon hearth-wall liner adapted to contain molten metal, comprising: 35. The apparatus of claim 34, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors. 36. The apparatus of claim 34, wherein the neutron generator comprises the photon generator and a neutron-emitting target. 37. The apparatus of claim 36, wherein the neutron-emitting target includes beryllium. 38. The apparatus of claim 34, wherein the photon generator is a linear accelerator capable of producing bremsstrahlung radiation. 39. The apparatus of claim 38, wherein the bremsstrahlung radiation has an energy of about 3 to about 8 MeV.