Method and apparatus for measuring ice thickness on substrates using backscattering of gamma rays
First Claim
1. A method for measuring ice buildup on an outer surface of a substrate, comprising:
- providing a gamma ray source in a source holder, the gamma ray source producing a beam of primary gamma rays having sufficient energy to penetrate through said substrate;
providing a photodetection means behind said source holder and positioning said source holder adjacent to an inner surface of said substrate so that the beam of primary gamma rays are directed through said substrate away from the photodetection means, wherein the source holder shields said photodetection means from primary gamma rays from the gamma ray source and shields said photodetection means from at least some of the gamma rays scattered in said substrate; and
measuring an intensity of backscattered gamma rays at said photodetection means and determining from said intensity of gamma rays a thickness of ice buildup on said outer surface of said substrate.
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Abstract
The present invention provides a method and apparatus for in situ measuring thicknesses of ice buildup on airfoil. The method and device uses a probe including a radioactive 241 Am gamma ray source producing 60 keV gamma ray photons which penetrate through the airfoil substrate and a photodetector mounted behind the source for detection of backscattered gamma rays. The probe is mounted on the interior of the airfoil and secondary radiation is backscattered within the ice layer and back through the airfoil substrate to the photodetector. The shape and density of the source holder in addition to the geometrical arrangement of the source and detector with respect to the airfoil substrate are used to block a substantial fraction of gamma rays backscattered in the airfoil substrate thereby favoring scattering in the ice layer over that in the airfoil material.
45 Citations
24 Claims
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1. A method for measuring ice buildup on an outer surface of a substrate, comprising:
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providing a gamma ray source in a source holder, the gamma ray source producing a beam of primary gamma rays having sufficient energy to penetrate through said substrate; providing a photodetection means behind said source holder and positioning said source holder adjacent to an inner surface of said substrate so that the beam of primary gamma rays are directed through said substrate away from the photodetection means, wherein the source holder shields said photodetection means from primary gamma rays from the gamma ray source and shields said photodetection means from at least some of the gamma rays scattered in said substrate; and measuring an intensity of backscattered gamma rays at said photodetection means and determining from said intensity of gamma rays a thickness of ice buildup on said outer surface of said substrate. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for measuring an ice layer buildup on an outer surface of an airfoil, comprising:
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a) at least one probe mounted on an interior surface of an airfoil, said at least one probe including a source holder containing a source of gamma rays having energies sufficiently high to penetrate through said airfoil, a photodetection means located behind said source holder for measuring an intensity of backscattered photons, the photodetection means being positioned with respect to said source holder so that said source holder blocks primary gamma rays from said source from impinging on said photodetection means and shields said photodetection means from at least some secondary gamma rays backscattered in said airfoil, and wherein gamma rays emerging from said source holder are directed away from said photodetection means; and b) processing means connected to said photodetection means for calculating a thickness of an ice layer from said intensity of backscattered gamma rays. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification