WO2009066023A2

WO2009066023A2 - Collimator for a non-destructive testing device using gamma radiography

Info

Publication number: WO2009066023A2
Application number: PCT/FR2008/001246
Authority: WO
Inventors: Daniel Roger Chauveau
Original assignee: Institut De Soudure; Blettner, Alexis
Priority date: 2007-09-05
Filing date: 2008-09-05
Publication date: 2009-05-28
Also published as: FR2920587B1; WO2009066023A3; FR2920587A1

Abstract

The invention relates to a collimator (1) comprising a housing (2) of substantially tubular shape designed to accommodate a source (S) emitting ionizing radiation and an exit window (3) communicating with the radiation source (S) for focusing the emitted radiation onto a target. The invention is such that the wall of the collimator (1) around the substantially tubular housing (2) has a variable thickness defining a thickness of said collimator (1) to be penetrated by all the rays emitted from the radiation source (S) placed in said housing (2), this thickness being sufficient but optimized, depending on the source and the constituent material(s) of the collimator, so as to ensure that sufficient and substantially constant attenuation of said rays irrespective of their radiation direction, with the exception of those focused by the window (3) of the collimator (1). Application to non-destructive testing devices using gamma radiography.

Description

Collimator for non-destructive gammagraphy monitoring device.

The present invention relates to the field of non-destructive testing devices by weld radiography, integrated radiation protection and in particular it relates to a collimator for such devices.

Ionizing radiation control such as using X-rays or gamma rays is very widely used in the industrial sector because it allows non-destructive testing of materials in order, in particular, to assess defects in the homogeneity of the metal, especially in welding seams, but it also allows the identification of defects in materials and the evaluation of corrosion. Indeed, the X or gamma rays are electromagnetic waves of high energy generated by vacuum tubes or highly radioactive elements such as rTterbium, Iridium 192, Selenium, etc. When they cross the material, the radiation undergoes absorption depending on the thickness and the density of the medium through which it passes. The radiation emerging from the object to be inspected then impresses a radiographic film which, after chemical development, gives a negative image of the examined part. A defect will be all the better detected that it has a significant dimension in the direction of radiation.

One of the main advantages of this type of control is that the radiographic film thus created constitutes an archival control document that can be taken back, studied and discussed after the taking. Such ionizing radiation control is therefore of vital interest in the inspection of weld beads.

Gamma radiography due to the use of very high energy ionizing radiation makes it possible to control materials of great thickness but subjects the operators to a risk of external exposure that is not negligible. Also, an ionizing radiation control device such as a gamma radiation control device using radioactive sources requires a significant implementation of protection means, because of the danger associated with the exposure of workers and the public. radiation. It is therefore imperative that the proposed tools guarantee the control of the risks of this activity. Indeed, the regulatory requirements concerning the use of ionizing radiation to perform non-destructive inspections on site are increasingly severe in terms of radiation protection. The on-site control devices generally consist of a gamma or gamma projector whose function is to store a radioactive source in a protection and to attenuate the radiation emitted by the latter when the device is not in operation. An ejection device consisting of a sheath provided with an irradiation tip or possibly a collimator is connected to the gamma ray while a remote control device will be used to control the ejection of the source towards the tip of irradiation or collimator during a shot. It is thus possible to define a safety perimeter around the test area, the operator being at the remote control and able to command the sending of said source to the test location without the risk of being subjected to radiation during the test. shooting at the level of the irradiation tip. The collimator serves to reduce the risk of irradiation of the operator.

In order to be able to take a radiogram of the whole of the weld, it is necessary that the film to be impressed is correctly positioned and that the radiation source is also well positioned. Therefore, it is necessary to fix the irradiation tip or the collimator at the level of the test weld in the most appropriate manner and as quickly as possible to limit the risks for the operator.

The use of collimators available in France is made difficult and more and more restrictive because of the nature of the attenuating material used constituted by depleted uranium. This substance is weakly radioactive and has a high toxicity, both radiological and chemical, as long as it is inhaled or ingested.

In addition, the collimation angle well above 90 ° does not allow easy management of radiation protection. The radiation beam often far exceeds the area to be examined.

In addition, the collimators are not all designed to adapt to the irradiation tip, but are intended to directly receive the active radio source. The collimators are generally made of materials protecting ionizing radiation called attenuating materials such as tungsten, depleted uranium or lead. These collimators are generally made in the form of a solid piece monomaterial having a very high weight which does not always facilitate its use or its establishment for shooting and also entails a high cost.

Thus, document FR 2 331 127 discloses an irradiation device using, as a radiation source, radioactive elements arranged on a mobile source support placed inside a protective shield, said support being able to successively occupy a position irradiation and a position of non-irradiation, means for placing said source in one and the other positions. These means comprise a spring rotation system allowing said source to occupy both positions and locking means for immobilizing said source support in the irradiation position for a predetermined time.

Thus, the protective shield is of material capable of absorbing radioactive radiation, and comprises in its center a recess opening on a channel opening outwardly. This recess contains a disc provided with a cell in which is housed the radioactive element. The disk is rotatable mountable to allow positioning of the radioactive element opposite or not the channel to the outside.

This shield has a substantially oblong shape but this elongation of the shape extends around the channel provided for the passage of the beam of radiation and not around the circular housing in which the source is housed, the thickness of the shield around this housing being substantially constant, which leads to thicknesses traversed by the variable radiation.

Such a shield of protection remains massive and relatively expensive.

Document DE 1961933 also proposes a protective body having a protective material whose thickness is determined to guarantee the attenuation around a tabular housing in which is housed the source of irradiation. This protective body has substantially a pear shape around this tabular housing.

However, it can be seen that the variation of the thickness is not really optimized in order to define a ratio between the quality of the radiation absorption and the quantity of protective material required, the thickness traversed by two radiations according to different directions not being constant. Such a shield of protection remains heavy and massive, so expensive.

Therefore, there is a need for collimators particularly adaptable to existing irradiation tips, having high radiation protection guarantees while offering if possible a weight lower than current collimators, thus requiring less material to present an economically more cost advantageous while offering high radioprotection qualities.

For this purpose, the purpose of the present invention is to propose a collimator, in particular for a non-destructive radiography control device, comprising a substantially tabular housing for receiving a source emitting ionizing radiation, and an output window in communication with the radiation source. for focusing the radiation emitted by the radiation source towards a target, characterized in that the wall of the collimator around the substantially tabular housing has a variable thickness defining a thickness of said collimator to be crossed for all the radiation emitted from the radiation source placed in said housing, sufficient but optimized, depending on the source and the material (s) constituting the collimator, to ensure a sufficient and substantially constant attenuation of said radiation whatever their direction of radiation, with the exception of those focused by the collimator window.

Thus, very advantageously, by varying the thickness of the collimator around the radiation source while maintaining a through thickness sufficient to attenuate all the radiation, it ensures the effective and almost constant attenuation of said radiation while limiting the amount of radiation. material to be used, with respect to shapes approximating the cylindrical bar shape or like those of prior art documents mentioned above in which material is superfluously present.

The collimator of the invention, due to the variation of the thickness around the tabular housing makes it possible to optimize the attenuation efficiency and the weight of the material used. Preferably, the variation of the thickness of the collimator to be crossed for the radiations is determined so that the attenuation across the material or materials constituting the collimator is constant.

According to a first variant embodiment, the collimator is arranged to fit on an irradiation tip enclosing the radiation emitting source.

According to a second variant, the collimator is arranged to fit the end of the sheath to directly receive the irradiation source.

According to a particularly preferred embodiment of the invention, said collimator has an optimized profile defining a collimator of substantially pear-shaped shape (substantially pomegranate or pear-shaped) around the tabular housing, thus defining a constant thickness of the attenuation material. to cross for all the rays emitted by the radiation source placed in said housing, with the exception of those focused by the collimator window.

This optimized profile is a theoretical profile that results from a calculation and has a variable thickness generating when applied to the 3 dimensions of the collimator, a pomegranate or pear shape that is called pear-shaped.

The invention advantageously makes it possible to limit the costs associated with the (x) material (s) used while offering a sufficient and constant attenuation of the radiation, that is to say an effective protection.

Very advantageously, the collimator according to the invention further comprises means for positioning the source opposite the exit window, in said collimator. When the source is enclosed in an irradiation tip, the positioning means are used to adjust the position of the tip in said collimator so as to position the source facing the collimator window.

According to an alternative embodiment, the collimator according to the invention can be made in one piece in a homogeneous heavy material, in particular by molding, machining or sintering.

According to a preferred embodiment of the collimator according to the invention, the housing in which is housed a radiation-emitting source is formed in a primary tube on which is reported a ring or sleeve whose inner wall is adapted to be positioned on the tube primary and whose thickness varies, tube thickness and the thickness of the ring together defining a collimator thickness, preferably variable such that the radiation emitted by the source all through a sufficient thickness of material (x) attenuating (s) and preferably optimized with respect to their attenuation, regardless of their direction of propagation of radiation.

This crossed thickness is identical for all the radiation when the collimator consists of a single attenuation material.

Thus the outer wall of the ring is substantially of convex shape so as to confer on the collimator around the position in which the radiation source will be placed, a piriform shape so that the radiation all through a thickness of identical attenuating material are thus attenuated steadily regardless of the direction of propagation of the radiation.

This embodiment may be made of a single material, in particular by sintering, machining or overmolding.

It is also possible to use different materials to make the two pieces of said collimator. Thus advantageously, the collimator can be adapted to activities of different sources or types of radioelements such as TYrterbium, Iridium,

Selenium ... In particular, by using several attenuating materials, one makes possible a better attenuation of the radiation due to the complementary attenuation of the energy lines of the radioelement used.

When the collimator is made of materials having different attenuations, the profile of the collimator is defined as a function of the penetration thickness of said materials and of their attenuation characteristics to obtain a sufficient attenuation and substantially constant whatever the direction of the radiation.

Furthermore, according to a particularly advantageous variant, the collimator according to the invention may comprise closure means remote from the window, said means being constituted by means for driving in rotation or in translation of the ring relative to the primary tube. .

Depending on the shooting to be performed: ellipse, shot on plane / plane tube, shot on large plane / plane wall, the window such as cylindrical, rectangular, can be cut directly into the collimator or constituted by a diaphragm attenuating material implanted in a hole in the collimator. This diaphragm can be either fixed or removable. In the latter case, the change of diaphragm makes it possible to adapt the collimator to different shots during the same campaign.

The present invention also relates to a device for non-destructive testing by gamma radiation of the type comprising in particular an irradiation source enclosed in a shielded housing, a source guide sheath comprising a collimator according to the invention is mounted directly on the sheath of guide is mounted on an irradiation tip.

The invention will now be described in more detail with reference to the drawing in which:

FIG. 1 represents a view in longitudinal section of a collimator according to a first example of the invention;

FIGS. 1a and 1b respectively represent the view of FIG. 1 and an example of the result of an optimized profile calculation; Figure 2 shows a longitudinal sectional view of a variant of the collimator of Figure 1;

FIG. 3 represents a view in longitudinal section of a collimator according to a second example of the invention;

FIG. 4 represents a view in longitudinal section of a collimator according to another example of the invention;

FIG. 5 represents a schematic view of FIG.

Figure 6 shows a sectional view of a collimator mounted on two parts to be controlled.

A collimator 1, 1, 10 or 100 according to the invention comprises a housing 2 of tubular shape sized and arranged to receive a commercial irradiation tip containing a source S emitting ionizing radiation and a side exit window 3 facing the source of radiation to focus the emitted radiation to a target to be photographed.

In the form of collimator 1 shown in Figure 1, the housing 2 is formed in a primary tube 4 of attenuating material. This attenuating material may be tungsten, tin, lead, a polymer loaded with attenuating material, bismuth or any other suitable material, to allow effective attenuation of the radiation. This material is therefore chosen as a function of the radioelement constituting the source S, which may be Iridium, Selenium, rtterbium or other.

On this primary tube 4 is attached a ring 5 of material also attenuating. This attenuating material may be identical to that of the primary tube 4 or be different, which allows to thwart the effectiveness of the attenuation of the different materials used. This ring 5 associated with the primary tube 4 defines a collimator 1 whose thickness traversed by the radiation is sufficient to obtain the desired attenuation, this attenuation is constant for all directions of the radiation. Thus, the wall of the collimator 1 formed of the primary tube 4 and the ring 5 around the tabular housing has a variable thickness, which limits the amount of material used to form the ring 5, but this variable thickness of the ring 5 is also defined so as to allow a thickness constant through said collimator for all the radiation emitted from the radiation source placed in said housing. This thickness traversed by each radiation ensures their sufficient and constant attenuation, obviously with the exception of those focused by the window 3 of the collimator 1.

As can be seen in this figure 1, the collimator 1 has a pear-shaped shape that optimizes its weight while ensuring its effectiveness. The sectional view of this FIG. 1 shows a "cosine profile" for the collimator 1.

This optimized profile is a theoretical profile that results from a calculation (see Figure la) so that the attenuation of ionizing radiation in the angular sector - α1 to α2 is constant. That is to say that the thickness traversed by all the radiation is sufficient to guarantee the attenuation of these radiations, attenuation sufficient and substantially constant.

The extreme value of αl is - 90 °. The value of this angle is generally limited in order to benefit from a plane base.

The extreme value of α 2 corresponds to + 90 ° but this value is generally limited to the connection angle with the tabular part

The profile resulting from this calculation, has a variable thickness generating when it is applied to the three dimensions of the collimator, a shape in pomegranate or pear which is called pear-shaped. In small collimators, the attenuation in the air (OAl) is neglected, since this has little impact on the variation of the external profile. In case the concept is applied to large collimators, it may be wise to take this into account.

The following definitions apply to small collimators

a) where the primary tube 4 and the ring 5 are made of identical materials.

The traversed thickness of Al A3 attenuating material is identical regardless of the angle α that is generally limited for manufacturing considerations between the aforementioned terminals.

In this case, as an example, the profile is calculated as follows: let r be the radius of the tabular recess: r = OA is e ₀ the thickness traversed for alpha = 0: AB = eo

The coordinates of the point B 'describing the profile is expressed by: x = r + βQ cos α y = r tang α + eo sin α

b) case where the primary tube 4 and the ring 5 are made of materials with different attenuations

R = ratio between the values (depending on the fineness of the optimization sought, these values can be the half-transmission, the deci-transmission or result of the application of the law of Béer) characteristics of the attenuation of the materials of tube 4 and ring 5, K = constant

The distance traversed by the Al A2 / R + A2A3 + K radiation is identical regardless of the angle α between the above-mentioned terminals. c) where two or more materials are considered AiAjTRi + Aj Ak / Rj + AmAn + K

Ri, Rj ... = ratio between the characteristic values of the attenuation of the material of the layer and the least attenuating material of the collimator.

In the primary tube 4 and the ring 5 is provided an outlet port 6, for example of slightly conical cylindrical shape in which is placed a diaphragm 7 made of attenuating material and which defines the exit window 3 of the beam of radiation.

This diaphragm 7 can be fixed or be made removable, fixed with screws and a centering pin 8, on the collimator 1 so that it is possible to change the diaphragm 7 to obtain exit windows 3 different dimensions depending on the desired shots.

A variant of the collimator 1 in two parts of Figure 1 may further be closed remotely, that is to say that one can provide means for driving in rotation or in translation of the ring 5 relative to the primary tube 4 so that the light of the primary tube 4 and the light of the ring 5 are facing each other in the open position of the window 3 for a shot and the drive in rotation or in translation of the ring 5 relative to the primary tube 4 shift the two lights which close the window 3.

FIG. 2 shows two variants of the collimator of FIG. 1. In the left-hand part of FIG. 2, the variation of the thickness of the collimator is obtained by a primary tube 4 on which place a ring 5a whose machining allows said ring 5a substantially has a profile A shaped double cone.

In the right part of FIG. 2, the variation of the collimator collector is obtained by placing on the primary tube 4 cylinders 9 of different lengths or by winding sheets so as to determine the profile B, or at least to get as close as possible to this theoretical profile to ensure sufficient attenuation and substantially constant, the material used and the thickness of said cylinders 9 of different lengths constituting a ring 5b or sheets being adapted to the source S used and the material constituting the primary tube 4. Thus, it is possible to propose a primary tube 4 tungsten and 9 lead cylinders.

FIG. 3 shows a variant of the collimator according to the invention in which the window 30 is located in the axis of the collimator 10. Such an axial output collimator 10 can be used, for example, for applications where it can be more tolerant with the geometric blur and thus uses the large dimension of the source S to shoot in the axis of the collimator 10. In the light 6 'formed in the axis of the collimator 10, it is possible to set up a diaphragm 7 for adapt to the area to be irradiated.

The collimator 100 of FIG. 4 is in a form represented schematically tabular. As can be seen, it comprises means for positioning said collimator 100 on an irradiation tip E so as to adjust the true position of the source S and the collimator 100. These means preferably consist of a ring 11 arranged on the collimator 100 and through which is engageable the irradiation tip E to be housed in the collimator 100.

This collimator 100 and this ring 11 are preferably dimensioned so as to accommodate the different types of irradiation end-pieces E, a clamping screw 1 protruding into the ring 11 enabling the end-piece E to be fixed in said ring 11 and in particular the adjustment of the position of the collimator 100 to the true position of the source S.

On the irradiation tip E, there is indeed also provided a ring 1 Ib, for example fixed by means of a screw clamp, a screw strapping system. This ring 1 Ib engageable in the ring 11, has a latching groove 1 Ic and cooperates with the screw l ia to fix the irradiation tip E in the collimator 100. This ring 11b allows in particular to adjust the actual position of the source of radiation S by positioning the irradiation tip E accurately along its longitudinal axis in the collimator 100. In fact, given the manufacturing tolerances of the irradiation tips and their wear, the actual position of the source at a exposure is specific to each irradiation end E. This adjustment is performed once.

This ring 1 Ib then allows to maintain the correct positioning once and for all of the source S with respect to the output window 3 of the collimator 100, at each reset of the irradiation tip E in the collimator 100 snap-fastening with screw ia. This connection is fast and easy to dismount. Such a device does not therefore affect the integrity of the irradiation tip E. These positioning means are conceivable on all the collimators described above.

In order to correctly position a control device on a test piece provided with a collimator according to the invention, it is possible to provide positioning aid means consisting of light sources, of laser, which are put in place on the ring 11. in the collimator 100, help to define the correct positioning of said device on the part, for example by means of a mounting device. Thus, it is possible to insert in the collimator a laser source carrying a ring enabling it to be fixed on said ring 1 with the aid of the locking screw 11a.

The collimator 1 can also be positioned precisely mechanically on a part to be controlled such as a tubular conduit C1 by means of mounting means of said collimator 1 on the part, said mounting means possibly being constituted by pads removably mounted. relative to the collimator 1 and allowing its adaptation to the test piece C1. Thus, the mounting means may consist of a base or frame 21 made integral with the collimator 1, and on which are releasably fixable pads 20a allowing the positioning on a tubular conduit C1. These pads 20a can be removed and replaced by pads 20b which allow positioning and mounting of the collimator 1 on a tubular conduit C2 with a diameter other than Cl as can be seen in FIG.

The invention is of course not limited to the embodiment described but also encompasses the variants defined in the claims.

Claims

1. Collimator (1, 1 ', 10, 100), in particular for non-destructive gammagraphy monitoring device, comprising a housing (2) of substantially tubular shape arranged to receive a source (S) emitting ionizing radiation and a window of output (3, 30) in communication with the source (S) of radiation for focusing the emitted radiation towards a target, characterized in that the wall of the collimator (1, 1 ', 10, 100) around the housing (2) substantially tubular having a variable thickness defining a thickness of said collimator (1, 1 ', 10, 100) to be crossed for all the radiation emitted from the source (S) of radiation placed in said housing (2), sufficient but optimized, depending on the source and the material (s) constituting the collimator, to ensure a sufficient and substantially constant attenuation of said radiation whatever their direction of radiation, with the exception of those focused by the collimation window (3, 30). (1, V, 10, 100).

2. Collimator according to claim 1, characterized in that the collimator further comprises means for positioning the source facing the exit window in said collimator.

3. Collimator according to one of claims 1 and 2, characterized in that the collimator (1, 1 ', 10) is arranged to fit on an irradiation tip containing the source (S) radiation emitter.

4. Collimator according to claims 2 and 3, characterized in that, when the source (S) is enclosed in an irradiation tip (E), said positioning means for adjusting the position of the tip in said collimator so as to position the source facing the collimator window, are preferably constituted by a ring (11) formed on the collimator (100) and through which is engageable the irradiation tip (E) to come housed in the collimator (1, l ', 10, 100), a clamping screw (l ia) projecting into the ring (11) for fixing the end piece (E) in said ring (11) and in particular adjustment the position of the collimator (1,1 ', 10, 100) at the true position of the source (S), by cooperation with a ring (1 Ib), provided on the tip (E).

5. Collimator (1, l ', 10, 100) according to one of claims 1 to 4, characterized in that the collimator (1, l', 10, 100) is arranged to adapt to the end of a sheath for directly receiving the source (S) emitting radiation.

6. Collimator according to one of claims 1 to 5, characterized in that the collimator is made in one piece in a homogeneous heavy material.

7. Collimator (1, 1 ', 10, 100) according to one of claims 1 to 6, characterized in that the housing (2) in which is a source (S) radiating radiation is formed in a primary tube (4) on which is reported a ring (5, 5a, 5b) whose inner wall is adapted to be positioned on the primary tube

(4,) and whose thickness varies, the thickness of the tube (4) and the thickness of the ring (5, 5a,

5b) defining together a collimator thickness (1, 1 ', 10, 100) variable such that the radiation emitted by the source (S) all pass through a sufficient thickness of material (x) attenuating) and optimized vis-à-vis their attenuation.

8. Collimator (1, 1 ', 10, 100) according to claim 7, characterized in that the outer wall of the ring (4) is substantially convex so as to confer the collimator (1) around the position in which will be placed the radiation source (S), a piriform shape such that the thickness of the tube (4) and the thickness of the ring (5) together define a variable collimator thickness such that the radiation emitted by the source ( S) all pass through a thickness of attenuating material sufficient for their attenuation whatever the direction of propagation of the radiation.

Collimator (1 ') according to claim 8, characterized in that the variation of the thickness of the collimator (1 ') is obtained by a primary tube (4) on which is set up a ring (5a) which has substantially a profile in the form of double cone.

10. Collimator (1 ') according to claim 8, characterized in that the housing (2) in which is housed an irradiation tip containing a radiation emitting source is formed in a primary tube on which is reported a plurality of cylinders (9) of different lengths constituting a ring (5b).

11. A collimator according to claim 8, characterized in that the housing (2) in which is a source (S) radiating radiation is formed in a primary tube (4) around which are wound sheets forming a ring.

12. Collimator (1, I ') according to claim 1 to 11, characterized in that, when the window (3) is lateral outlet, the collimator (1, I') comprises closing means remote from the window (3), said means being constituted by means for driving in rotation or translation of the ring (5) with respect to the primary tube (4).

13. Collimator (10) according to one of claims 1 to 11, characterized in that the window (30) is axial output.

14. Collimator (1, 1 ', 10, 100) according to one of claims 12 and 13, characterized in that the window (3) is constituted by a diaphragm (7) of attenuating material implanted in a light (6) arranged in the collimator (1, 1 ').

15. Collimator (1, l ', 10, 100) according to claim 14, characterized in that the diaphragm (7) is removable.

16. The collimator (1, 1 ', 10, 100) according to one of claims 1 to 15, characterized in that it comprises means for mounting said collimator (1, 1 ', 10, 100) on a part to be controlled, said mounting means being able to consist in particular of pads (20a, 20b) removably mounted by relative to the collimator and allowing its adaptation on the part to be controlled.

17. A non-destructive radiography control device comprising, in particular, an irradiation source enclosed in a shielded casing, a source guide sheath, characterized in that it further comprises a collimator according to one of claims 1 to 16.