GB2346966A

GB2346966A - Radiodiagnostic method and apparatus

Info

Publication number: GB2346966A
Application number: GB9903836A
Authority: GB
Inventors: John Oliver Wilson Norris
Original assignee: AEA Technology PLC
Current assignee: Ricardo AEA Ltd
Priority date: 1999-02-20
Filing date: 1999-02-20
Publication date: 2000-08-23
Also published as: GB9903836D0

Abstract

For the examination of matter, such as oil, in spaces within opaque components in an apparatus, such as an engine or machinery, a source 15a of penetrating radiation is located in or on a component within the apparatus to reduce the path length over which the penetrating radiation has to traverse. The source 15a can also be located to reduce the number/thickness of components in the path which attenuate the radiation but which are to be excluded from the measurement.

Description

Radiodiaanostic Method and Annaratus The invention relates to radiodiagnosis in which penetrating radiation is employed to provide information about content of matter in a space within a component or between components which are opaque to visible light.

The use of penetrating radiation to provide information about matter which is hidden from view has been widely adopted and, for example, has found particular application in examining oil penetration into those spaces within machinery and engines where lubrication is required. Typically, the apparatus such as an engine to be examined is positioned between a source of penetrating radiation and a detector. This known arrangement is described more fully below in relation to Figure 1.

A problem with such known arrangements is that the required information has to be derived from the detected attenuation of the penetrating radiation which is caused by the material of interest, the oil in the case of the engine example described. Consequently, not only does the source of radiation have to be powerful enough to penetrate all of the engine components between the source and the detector, but also, the incremental attenuation effect by the material of interest is relatively small compared with the attenuation caused by the surrounding metal components.

This problem is ameliorated in accordance with the present invention which provides, in one of its aspects, a method of examining content of matter in a space within a component or between components which are opaque to visible light, which method comprises locating on or in the component or one of the components a source of penetrating radiation so as to direct radiation from the source across the said space, and positioning a detector to receive radiation from a region of the said space.

By penetrating radiation we mean radiation which is capable of penetrating the said matter and the said component or components whilst being attenuated thereby.

Typically, the penetrating radiation employed for the purposes of the invention will be gamma radiation, or X- radiation or neutrons.

The invention provides, in another of its aspects, apparatus comprising at least one component having a space therein for containing material obscured from visual examination, a source of penetrating radiation located on or in the component, a detector positioned to detect radiation from the source which has passed through the space and any material contained therein, and means for providing an indication of changes in the said material which affect the extent to which the radiation passing therethrough is attenuated.

In one arrangement according to the invention, the apparatus comprises machinery or an engine in which the said spaces contain oil during normal operation and the source and detector are positioned to provide diagnostic information about oil in the spaces during operation of the machinery or engine.

Preferably, the source comprises a radioactive element or compound which emits the penetrating radiation and is attached to or forms part of the component on or in which it is located.

Conveniently, the source is provided by subjecting the component or a part thereof to ion beam irradiation such as to activate at least one constituent of the component by transmutation of the constituent into a radioactive element.

Alternatively, the source comprises a pre-prepared source attached to or embedded in the component.

A specific method and apparatus embodying the invention will now be described by way of example and with reference to the drawings filed herewith, in which: Figure 1 is a diagrammatic illustration of a prior art arrangement, and Figure 2 is a corresponding diagrammatic illustration of an embodiment of the invention.

Referring to Figure 1, which shows a known technique, an apparatus 11 to be interrogated, is represented as a casing 12, a central spindle 13 and an intervening space 14 the contents of which are to be measured. The apparatus 11 is positioned between a collimated external source 15 of penetrating radiation and a detector 16.

Typically, for the radiation to penetrate the entire apparatus, a powerful source 15 is required.

The attenuation of the radiation between the source and the detector is the integrated attenuation of each component in the"line of sight"and, in the example shown in Figure 1 will be the sum of the attenuation by twice the thickness of the casing 12, twice the nradiusu of material in the intervening space 14 and twice the radius of the central spindle 13.

Attenuation of the more energetic gamma rays is approximately proportional to material density. It will be seen that the attenuation is dominated by the central spindle.

Referring to Figure 2, apparatus 11 to be interrogated is represented identically with that shown in Figure 1 and the same components are identified with the same reference numerals. However, in the embodiment of the invention as shown in Figure 2, the source 15a of penetrating radiation is located at the surface of the central spindle 13.

With this configuration, the attenuation is that effected by the"radius"of material in the space 14 added to that effected by one thickness of the casing 12.

As a consequence a source 15a of greatly reduced strength is required which simplifies the radiological problems and extends the range of applications for the technique.

In addition, the attenuation is no longer dominated by that effected by the central spindle 13 so that the precision and accuracy of the measurement are improved.

This is illustrated, by way of example, as follows: Assume the casing 12 and central spindle 13 are of steel (density = 8gm/cm) with a casing wall thickness of 3 mm, outside diameter of 40 mm, and a central spindle diameter of 10 mm. To simplify the illustration we compare the effect upon the attenuation of filling the space 14 with water (density = 1 gm/cm).

Adopting the prior art configuration of Figure 1: absorption coefficient when empty = 3 x 8 + 10 x 8 + 3 x 8 = 128 log units absorption coefficient when full = 3 x 8 + 13 + 10 x 8 + 13 + 3 x 8 = 154 log units ratio of absorption coefficients full/empty = 154/126 = 1.22 loe units.

Adopting the configuration of Figure 2: absorption coefficient when empty = 3 x 8 = 24 log units Absorption coefficient when full = 3 x 8 + 13 = 37 log units ratio of absorption coefficients full/empty = 37/24 = 1. 54 log units.

Because of the overall reduction in absorption and the reduced distance between source and detector, the strength of the source required for the Figure 2 configuration can be reduced to approximately 1/20th of that required for the Figure 1 configuration.

The location of a suitable source 15a on or in the central spindle 13, or on or in any other component forming part of the apparatus under examination can be achieved in a number of ways. For example, the whole or a portion of the component can be activated in the same manner as that adopted for thin layer activation analysis. Alternatively, an activated token can be fixed to the component for example in the form of a small piece of foil, metal, or as a grub screw, nail, pin or the like. Or again, a commercially available"ready prepared"source from a supplier such as Amersham International can be purchased and attached or embedded into the component using whatever fastening option is most convenient.

An advantage of having the source 15a in a form separable from the component on or in which it is located is that it can be removed and repositioned if desired or removed completely when measurements have been completed, thus returning the apparatus under examination to an inactive state.

Activation referred to above for creating a source 15a may be effected by bombardment with high energy particles such as protons using an accelerator. Thus, for example, in a typical reaction with iron, the incoming proton displaces a neutron in the nucleus of an iron atom to form radioactive Co. This and other suitable examples of the type of nuclear reaction that can be used are as follows: Fe (p, n) to give Co 56Fe (d, n) to give 57Co 52Cr (p, n) to give 52Mn 65Cu (p, n) to give 65Zn 206Pb (p, n) to give 206Bi.

The examples above show that a range of common metals (iron, chromium, copper and lead) can all be transformed to give sources, illustrating the wide applicability of the technique.

The newly formed nuclide emits gamma rays which are attenuated as they pass through matter. It is the measurement of the attenuation of the gamma rays that enables information to be derived as to nature, composition and/or quantity of material in the path along which they have travelled. This is particularly useful when one has some fixed components, e. g. the walls of a vessel, and a variable component, e. g. the vessel's contents, because the differences in attenuation can be ascribed solely to differences in the variable component.

The type of detector 16 appropriate to this type of measurement is a standard gamma ray detector, which includes scintillation detectors (e. g. a sodium iodide crystal combined with a photomultiplier) and semiconductor detectors (e. g. a germanium or GeLi detector). Such detectors are routinely used for giving "real time"gamma ray fluxes, which can be analysed to give"real time"information about the composition of the path along which the gamma rays have travelled.

Accumulating dosimeters, e. g. film badges, or thermoluminescent dosimeters measure the dose accumulated over a period of time. One or more such dosimeters may also be used. Data obtained from this type of detector, when appropriately analysed, would give average values for the composition of the path between the source and detector.

The invention is not restricted to the details of the foregoing examples. For instance, it is possible for the detector 16 to be mounted in or on a component of the apparatus, even internally if desired and practicable.

This makes it possible even further to reduce the path length traversed by the penetrating radiation and can be adopted to provide an interrogation/measurement system operable at any time during normal use of the apparatus.

The use of the invention in engines or machinery has been referred to, with specific relevance for measurement of the distribution of fluid around moving components or oil in the sump of a moving car. Other applications include measurement of the height of liquid (e. g.. water, oil, paint) in an opaque container.

Claims

Claims 1. A method of examining content of matter in a space within a component or between components which are opaque to visible light, which method comprises locating on or in the component or one of the components a source of penetrating radiation so as to direct radiation from the source across the said space, and positioning a detector to receive radiation from a region of the said space.
2. Apparatus comprising at least one component having a space therein for containing material obscured from visual examination, a source of penetrating radiation located on or in the component, a detector positioned to detect radiation from the source which has passed through the space and any material contained therein, and means for providing an indication of changes in the said material which affect the extent to which the radiation passing therethrough is attenuated.
3. Apparatus as claimed in claim 2, comprising machinery or an engine in which the said spaces contain oil during normal operation and the source and detector are positioned to provide diagnostic information about oil in the spaces during operation of the machinery or engine.
4. A method or apparatus as claimed in any of the previous claims, wherein the source comprises a radioactive element or compound which emits the penetrating radiation and is attached to or forms part of the component on or in which it is located.
5. A method or apparatus as claimed in claim 4, wherein the source is provided by subjecting the component or a part thereof to ion beam irradiation such as to activate at least one constituent of the component by transmutation of the constituent into a radioactive element.
6. A method or apparatus as claimed in claim 4, wherein the source comprises a pre-prepared source attached to or embedded in the component.
7. A method substantially as hereinbefore described with reference to Figure 2 of the drawings filed herewith.
8. Apparatus substantially as hereinbefore described with reference to, and illustrated in, Figure 2 of the drawings filed herewith.