Apparatus and method for directly measuring the density of a thin layer

• US 4,641,030 A
• Filed: 12/13/1984
• Issued: 02/03/1987
• Est. Priority Date: 12/13/1984
• Status: Expired due to Term

• Current Assignee: Troxler Electronic Laboratories, Inc.
• Original Assignee: Troxler Electronic Laboratories, Inc.
• Inventors: Regimand, Ali
• Primary Examiner(s): Howell, Janice A.
• Application Number:
  US06/681,302
• Time in Patent Office: 782 Days
• Field of Search: 250/308, 250/358.1, 378/89
• US Class Current: 850/63
• CPC Class Codes: G01N 23/203 Measuring back scattering

Abstract

The present invention provides a nuclear radiation backscatter gauge which is capable of directly measuring the density of a thin top layer of material from a composite material comprised of the relatively thin top layer of material applied over an underlying base material. The gauge includes a nuclear radiation source and two radiation detector means so positioned with respect to the source as to form two geometrically differing source-to-detector relationships. A signal processing circuit responds to detected radiation from the two detector means to generate respective signals D_G1 and D_G2 representative of the components densities of the top and base layers as measured by the detector means. The density D_T of the thin top layer is then determined by a signal processing means from the relationship ##EQU1## wherein k₁ and k₂ are empirically derived instrument constants.

Claims

1. A nuclear radiation backscatter gauge for directly measuring from a composite material comprised of a relatively thin top layer of material applied over an underlying base material, the density D_T of the top layer, comprising

means for emitting nuclear radiation from a source into the relatively thin top layer of material and the underlying base material and for detecting radiation which is scattered therefrom at two geometrically differing source-to-detector relationships;

signal processing circuit means for responding to the detected scattered radiation at said two source-to-detector relationships and generating respective signals D_G1 and D_G2 representative of the composite densities of the top layer and base layer as measured at the respective source-to-detector relationships, and

signal calculating circuit means connected with said signal processing circuit means and operable for determining the density D_T of the top layer from the relationship ##EQU7## where k₂ and k₁ are empirically derived instrument constants.

2. A nuclear radiation backscatter gauge for directly measuring from a composite material comprised of a relatively thin top layer of material applied over an underlying base material, the density D_T of the top layer, comprising

nuclear radiation source means for directing radiation into the thin layer and the underlying base material;

two nuclear radiation detector means so positioned with respect to said source as to form two geometrically differing source-to-detector relationships;

signal processing circuit means operatively connected with each of said detector means for responding to detected radiation and generating respective signals D_G1 and D_G2 representative of the composite densities of the top layer and base layer as measured by the respective detector means; and

signal calculating circuit means connected with said signal processing circuit means and operable for determining the density D_T of the top layer from the relationship ##EQU8## where k₁ and k₂ are empirically derived instrument constants.

3. A nuclear radiation gauge according to claim 2 wherein the constants k₁ and k₂ are functionally related to the thickness X of the top layer, and said gauge includes input means for accepting operator input of the approximate thickness X of the top layer and means for providing to said signal calculating circuit means values for the constants k₁ and k₂ as a function of thickness X received by said input means.

4. A nuclear radiation gauge according to claim 2 including display means for displaying the value for D_T obtained by said signal calculating circuit means.

5. A nuclear radiation density measurement method for directly measuring from a composite material comprised of a relatively thin top layer applied over an underlying base material, the density D_T of the top layer, comprising the steps of:

directing nuclear radiation from a source into the thin material and the underlying base material;

detecting radiation which is scattered therefrom at two geometrically differing source-to-detector relationships and determining therefrom the composite densities D_G1 and D_G2 of the composite material as measured at the respective source-to-detector relationships; and

determining the density D_T of the top layer from the relationship ##EQU9## where k₁ and k₂ are empirically derived instrument constants.

6. A nuclear radiation density measurement method for directly measuring from a composite material comprised of a relatively thin top layer applied over an underlying base material, the density D_T of the top layer, comprising the steps of:

positioning at the surface of the top layer a nuclear backscatter density gauge having a nuclear radiation source and two nuclear radiation detector means so positioned with respect to the source as to form two geometrically differing source-to-detector relationships;

detecting backscattered radiation at the two detector means and determining therefrom the composite densities D_G1 and D_G2 of the composite material as measured by the two detector means; and

determining the density D_T of the top layer from the relationship ##EQU10## where k₁ and k₂ are empirically derived instrument constants.

7. A nuclear radiation density measurement method for directly measuring from a composite material comprised of a relatively thin top layer applied over an underlying base material, the density D_T of the top layer, comprising the steps of:

positioning at the surface of the top layer a nuclear backscatter density gauge having a nuclear radiation source and two nuclear radiation detector means so positioned with respect to the source as to form two geometrically differing source-to-detector relationships;

detecting backscattered radiation at the two detector means and determining therefrom the composite densities D_G1 and D_G2 of the top layer and base layer as measured by the two detector means; and

providing to the gauge the approximate thickness X of the top layer and calculating therefrom values for instrument constants k₁ and k₂, said constants being empirically derived instrument constants which are functionally related to the thickness X, and

determining the density D_T of the top layer from the relationship ##EQU11##