Apparatus and method for accurately measuring the density of materials with rough surfaces by radiation backscatter
First Claim
1. A method of measuring the density of a material having a rough upper surface by means of radiation backscatter, said method comprisingpositioning on the rough upper surface of the material a block of known density and thickness,directing gamma radiation from a source into the block and into the underlying material,obtaining from at least two geometrically differing source-to-detector relationships separate and distinct measurements of radiation scattered from the block and from the underlying material,calculating from said separate and distinct radiation measurements the density of an upper zone of predetermined thickness greater than the thickness of the block and which includes the thickness of the block as well as that portion of the underlying material which forms said rough upper surface,also calculating from at least one of said radiation measurements the composite density of the block and the underlying material, andcalculating from said composite density and from said upper zone density the density of the material as it exists below said rough upper surface thereof whereby the density value which is obtained is unaffected by the roughness of the surface of the material.
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Abstract
The present invention provides a nuclear radiation backscatter gauge and method by which an accurate determination of the density of a test material can be made, even though the test material may have surface irregularities or voids which would otherwise contribute significant error to the density measurement. The invention is based upon the use of a nuclear density gauge which is specially designed for measuring thin layers, and which is characterized by having a source and at least two separate detector systems mounted in geometrically differing relationships with respect to the source. Through the use of this type of gauge, in combination with a pad or block of known thickness and density, a measurement is made of the density of a top zone of a predetermined thickness which is greater than the thickness of the block and which thus encompasses not only the block but also an upper portion of the underlying material where the surface voids and irregularities exists. A density measurement is also made of the composite material, i.e. the block and the underlying material. The density of the composite material and the density of the top zone are then used to accurately determine the density of the material as it exists below the level of surface irregularities and voids.
46 Citations
9 Claims
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1. A method of measuring the density of a material having a rough upper surface by means of radiation backscatter, said method comprising
positioning on the rough upper surface of the material a block of known density and thickness, directing gamma radiation from a source into the block and into the underlying material, obtaining from at least two geometrically differing source-to-detector relationships separate and distinct measurements of radiation scattered from the block and from the underlying material, calculating from said separate and distinct radiation measurements the density of an upper zone of predetermined thickness greater than the thickness of the block and which includes the thickness of the block as well as that portion of the underlying material which forms said rough upper surface, also calculating from at least one of said radiation measurements the composite density of the block and the underlying material, and calculating from said composite density and from said upper zone density the density of the material as it exists below said rough upper surface thereof whereby the density value which is obtained is unaffected by the roughness of the surface of the material.
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2. A method of measuring the density of a material having a rough upper surface by means of radiation backscatter, said method comprising
positioning on the rough upper surface of the material a block of known density and thickness, directing gamma radiation from a source into the block and into the underlying base material, detecting at two detector locations that are in predetermined geometrical relationship with respect to the source two separate and distinct readings of radiation scattered from the block and from the underlying material and obtaining therefrom respective composite density measurements DG1 and DG2 of the block and the underlying material, calculating from said composite density measurements DG1 and DG2 the density DT of an upper zone of predetermined thickness greater than the thickness of the block and which includes the thickness of the block as well as that portion of the underlying material which forms said rough upper surface, calculating the difference between the measured density DT of said upper zone of predetermined thickness and the known density of the top block DTB to obtain a correction factor which represents the influence of the surface voids and irregularities present at the upper surface of the base material, correcting at least one of the composite density measurements DG1 or DG2 by adding said correction factor to obtain a corrected gauge density D1 or D2, and calculating from said corrected composite density Dj, where j is 1 or 2, and said known density of the top block DTB the density DB of the base material as it exists below said rough upper surface thereof whereby the density value which is obtained is unaffected by the roughness of the surface of the material.
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5. An apparatus for measuring the density of a material having a rough upper surface by means of radiation backscatter, said apparatus comprising
a block of material of known density and thickness adapted to be positioned on the rough surface of the test material, means for emitting nuclear radiation from a source into said block and into the underlying test material and for detecting radiation which is scattered therefrom at two geometrically differing source-to-detector relationships, first calculating means for responding to the detected radiation at said two source-to-detector relationships and for obtaining therefrom respective composite density measurements of the block and the underlying materials, second calculating means for calculating from said respective composite density measurements the density of an upper zone of predetermined thickness greater than the thickness of said block and which includes the thickness of the block as well as that portion of the underlying material which forms said rough upper surface, and third calculating means for calculating from said composite density and said upper zone density the density of the material as it exists below said rough upper surface thereof whereby the density value which is obtained is unaffected by the roughness of the surface of the material.
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6. An apparatus for measuring the density of a material having a rough upper surface by means of radiation backscatter, said apparatus comprising
a block of material of known density and thickness adapted to be positioned on the rough surface of the test material, source means for emitting gamma radiation into said block and into the underlying test material, detector means including at least two radiation detectors located in predetermined spaced relation to said source for obtaining respective radiation measurements which are distinctive from the radiation measured by any other detector, first calculating means operatively associated with said detector means for obtaining respective composite density measurements of the block and the underlying materials, second calculating means for calculating from said respective composite density measurements the density of an upper zone of predetermined thickness greater than the thickness of said block and which includes the thickness of the block as well as that portion of the underlying material which forms said rough upper surface, and third calculating means for calculating from said composite density and said upper zone density the density of the material as it exists below said rough upper surface thereof whereby the density value which is obtained is unaffected by the roughness of the surface of the material.
Specification