Binder permeated ionizing radiation shielding panels, method of construction of ionizing radiation shielding panels and an x-ray inspection system employing such panels

Abstract

An ionizing radiation shielding panel comprising a core layer, a first layer on a first side of the core layer and a second layer on a second side of the core layer, opposite to the first side. The core layer comprises radiation attenuation material which may be particles of barite. The first and second layers each comprise a permeable reinforcement structure and each of the first, second and core layers are permeated with a binder. In the construction of the panel, the binder is infected into a mould containing the other constituents of the panel. The ionizing radiation shielding panel can be used in the housing of an x-ray inspection apparatus.

Claims

1. An ionizing radiation shielding panel comprising: a core layer comprising a radiation attenuating material, a first layer on a first side of the core layer, comprising a permeable reinforcement structure; and a second layer on a second side of the core layer, opposite to the first side, comprising a permeable reinforcement structure, wherein the first layer, second layer and core layer are permeated with a binder.

2. The ionizing radiation shielding panel according to claim 1 wherein the permeable reinforcement structure of the first or second layers is a fabric and comprises glass fibre, or metal filaments, or carbon fibre, or poly-paraphenylene terephthalamide.

3. The ionizing radiation shielding panel according to claim 1 wherein the permeable reinforcement structure of the first layer or second layer, or both the first layer and the second layer comprises a woven fibre cloth, randomly orientated chopped fibre strands, or continuous filaments arranged in a mat, or an array of filaments.

4. The ionizing radiation shielding panel according to claim 1 wherein the first layer or second layer, or both the first layer and the second layer, comprises two or more sheets of the permeable reinforcement structure.

5. The ionizing radiation shielding panel according to claim 1 wherein the first layer or the second layer, or both the first layer and the second layer, comprises a binder spreader layer.

6. The ionizing radiation shielding panel according to claim 5 wherein the binder spreader layer is positioned between the permeable reinforcement structure and the core layer, and wherein the first layer or the second layer, or both the first layer and the second layer, further comprises a second permeable reinforcement structure positioned between the binder spreader layer and the core layer.

7. The ionizing radiation shielding panel according to claim 1 wherein the radiation attenuating material comprises greater than 65% of the binder permeated core layer by volume.

8. The ionizing radiation shielding panel according to claim 1 wherein the radiation attenuating material comprises an element having an atomic mass greater than 47 unified atomic mass units.

9. The ionizing radiation shielding panel according to claim 1 wherein the radiation attenuating material is barite.

10. The ionizing radiation shielding panel according to claim 1, wherein the radiation attenuating material is a particulate, and a diameter of a largest particle of the radiation attenuating material is not more than 10% of a thickness of core layer.

11. The ionizing radiation shielding panel according to claim 1 further comprising a mechanical load distribution structure.

12. The ionizing radiation shielding panel according to claim 11, wherein the mechanical load distribution structure comprises a metal sheet.

13. The ionizing radiation shielding panel according to claim 11, wherein the mechanical load distribution structure is embedded in the binder.

14. The ionizing radiation shielding panel according to claim 11, wherein the mechanical load distribution structure forms an external layer of the ionizing radiation shielding panel and is adhered to the binder.

15. An enclosure comprising a plurality of ionizing radiation shielding panels according to claim 1.

16. The enclosure according to claim 15, wherein the plurality of ionizing radiation shielding panels comprise one or more features that allow a labyrinth to be formed at a junction of at least two of the plurality of ionizing radiation shielding panels.

17. The ionizing radiation shielding panel according to claim 1, wherein at least one of the first layer and the second layer comprises a binder spreader layer, wherein the binder spreader layer is positioned between the permeable reinforcement structure of the first layer and the core layer and the permeable reinforcement structure of the second layer is positioned between the binder spreader layer and the core layer, and wherein the binder comprises a resin and permeates the binder spreader layer.

18. The ionizing radiation shielding panel according to claim 1, wherein at least one of the first layer and the second layer comprise a binder spreader layer positioned between a first mat of fibre strand and a second mat of fibre strand and the binder spreader layer comprises a resin that permeates the binder spreader layer.

19. An ionizing radiation shielding panel comprising: a core layer comprising a radiation attenuating material, a first layer on a first side of the core layer, comprising a permeable reinforcement structure; and a second layer on a second side of the core layer, opposite to the first side, comprising a permeable reinforcement structure, wherein the first layer, second layer and core layer are permeated with a binder, wherein at least one of the first layer and the second layer comprises a binder spreader layer and a second permeable reinforcement structure, wherein the binder spreader layer is positioned between the permeable reinforcement structure of the first layer and the core layer and the permeable reinforcement structure of the second layer is positioned between the binder spreader layer and the core layer, and wherein the binder comprises a resin and permeates the binder spreader layer.

20. The ionizing radiation shielding panel according to claim 19 wherein the permeable reinforcement structure of the first or second layers is a fabric and comprises glass fibre, or metal filaments, or carbon fibre, or poly-paraphenylene terephthalamide.

21. The ionizing radiation shielding panel according to claim 19 wherein the permeable reinforcement structure of the first layer or second layer, or both the first layer and the second layer comprises a woven fibre cloth, randomly orientated chopped fibre strands, or continuous filaments arranged in a mat, or an array of filaments.

22. The ionizing radiation shielding panel according to claim 19 wherein the first layer or second layer, or both the first layer and the second layer, comprises two or more sheets of the permeable reinforcement structure.

23. The ionizing radiation shielding panel according to claim 19 wherein the first layer or the second layer, or both the first layer and the second layer, comprises a binder spreader layer.

24. The ionizing radiation shielding panel according to claim 23 wherein the binder spreader layer is positioned between the permeable reinforcement structure and the core layer, and wherein the first layer or the second layer, or both the first layer and the second layer, further comprises a second permeable reinforcement structure positioned between the binder spreader layer and the core layer.

25. An ionizing radiation shielding panel comprising: a core layer comprising a radiation attenuating material, a first layer on a first side of the core layer, comprising a permeable reinforcement structure; and a second layer on a second side of the core layer, opposite to the first side, comprising a permeable reinforcement structure, wherein the first layer, second layer and core layer are permeated with a binder, and wherein at least one of the first layer and the second layer comprise a binder spreader layer positioned between a first mat of fibre strand and a second mat of fibre strand and the binder spreader layer comprises a resin that permeates the binder spreader layer.

26. The ionizing radiation shielding panel according to claim 25 wherein the permeable reinforcement structure of the first or second layers is a fabric and comprises glass fibre, or metal filaments, or carbon fibre, or poly-paraphenylene terephthalamide.

27. The ionizing radiation shielding panel according to claim 25 wherein the permeable reinforcement structure of the first layer or second layer, or both the first layer and the second layer comprises a woven fibre cloth, randomly orientated chopped fibre strands, or continuous filaments arranged in a mat, or an array of filaments.

28. The ionizing radiation shielding panel according to claim 25 wherein the first layer or second layer, or both the first layer and the second layer, comprises two or more sheets of the permeable reinforcement structure.

29. The ionizing radiation shielding panel according to claim 25 wherein the first layer or the second layer, or both the first layer and the second layer, comprises a binder spreader layer.

30. The ionizing radiation shielding panel according to claim 29 wherein the binder spreader layer is positioned between the permeable reinforcement structure and the core layer, and wherein the first layer or the second layer, or both the first layer and the second layer, further comprises a second permeable reinforcement structure positioned between the binder spreader layer and the core layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a cross-sectional view of a portion of an x-ray radiation shielding panel in accordance with the invention;

(3) FIG. 2 is a cross-sectional view of another embodiment of the x-ray radiation shielding panel comprising an additional layer;

(4) FIG. 3 is a perspective view of mechanical load distribution structure that could form an additional mechanical load distribution layer of the x-ray radiation shielding panel;

(5) FIG. 4 is a perspective view of a cutaway x-ray radiation shielding panel showing particularly the mechanical load distribution structure as an additional layer in the x-ray radiation shielding panel;

(6) FIG. 5 is a perspective view of an x-ray inspection apparatus comprising a radiation shielding cabinet formed of x-ray shielding panels in accordance with the invention;

(7) FIG. 6 is a cross-sectional view of two x-ray radiation shielding panels adjacent to one another;

(8) FIG. 7 is a cross-sectional view of two adjacent x-ray radiation shielding panels adjacent to one another in the context of the radiation shielding cabinet of FIG. 5;

(9) FIG. 8 is as perspective view of a mould used in the method of constructing an x-ray radiation shielding panel in accordance with FIG. 1;

(10) FIG. 9 is a flow chart of a method for constructing a panel of FIG. 1;

(11) FIG. 10 is a perspective exploded view of the mould of FIG. 8 with all the layers and the method of FIG. 9 placed in the mould;

(12) FIG. 11a is a cross-sectional view of a vacuum port in the mould of FIG. 8, after the mould has been filled with the components for thrilling the x-ray radiation shielding panel;

(13) FIG. 11b is a cross-sectional view of a resin input port in the mould of FIG. 8, after mould has been filled with the components for forming the x-ray radiation shielding panel; and

(14) FIG. 12 is a cross sectional view of an embodiment in which a portion of the mould forms an exterior layer of the finished panel, during the moulding process.

DETAILED DESCRIPTION

(15) FIG. 1 is a cross-sectional view of an x-ray shielding panel 100 for use in an x-ray inspection apparatus. The radiation shielding panel comprises a core layer 102, a first layer 110 and a second layer 120. The core layer 102 is sandwiched between the first layer 110 and the second layer 120. The core layer comprises an aggregate of radiation attenuating material 104 which, in this example, is an aggregate of barite.

(16) A binder 106 is present through all of the layers of the radiation shielding panel 100. The binder 106 is a resin that has been hardened during the manufacture process. In this example, the binder is a Sicomin™ 8100 epoxy resin. The hardened resin holds the layers of the radiation shielding panel 100 together. The first and second layers provide support to the core layer.

(17) The aggregate of barite 104 comprises particles of various sizes. The aggregate is chosen, or processed, to ensure that the maximum size of a barite particle is no more than 10% of the thickness of the core layer. This can be achieved by passing the radiation attenuating material through a sieve having a controlled hole size. In this example, the thickness of the core layer is 20 mm. This means that the maximum size of the barite particles is 2 mm. There is no minimum particle size. This ensures that there is a relatively even distribution of barite throughout the core layer 102 and, in particular, that there is a minimum path length of barite that radiation must pass through when traversing the panel. The resin 106 makes up only 25% of the core layer 102 by volume, with the rest of the core layer 102 being the aggregate of barite 104.

(18) The first layer 110 and the second layer 120 are both layers of Polymat™ Free Flow, available from Scott and Fyfe, Tayport Works, Lint Road, Tayport, Fife, Scotland, UK. The Polymat™ Free Flow layers comprise two glass fibre chopped strand mats 122, 123 as well as a binder spreader layer or resin spreader layer 124 formed by a polypropylene needle bonded core, positioned between the two mats of chopped glass fibre strands 122, 123. Resin 106 fills the gaps between the fibre of the mats as well as permeating the resin spreader layer 124. For each of the first and second Polymat™ layers, the outer mat of chopped glass fibre strands 122 forms an outer layer for the radiation shielding panel. The surface of the mat of chopped glass fibre strands, permeated with resin, is coated with a gel coat layer (not shown). The gel coat layer provides fire retardancy. It also ensures that the finished product is a consistent colour.

(19) The radiation shielding panel may comprise at least one other additional layer. Additional layers may be positioned between any of the layers already described above. FIG. 2 is a cross-sectional view of an embodiment of the radiation shielding panel of FIG. 1 comprising an additional layer 202. The additional layer, in this example, is positioned between the Polymat™ Free Flow layer 120 and the core layer 106.

(20) In one embodiment, the additional layer 202 is a radiation shielding layer which takes the form of an electrically conductive mesh. This radiation shielding layer is configured to reflect the low-frequency electromagnetic radiation that is often emitted by electronic machinery.

(21) In another embodiment, the additional layer 202 is a mechanical load distribution structure layer. The mechanical load distribution structure layer may be provided instead of, or in addition to, the radiation shielding layer for reflecting low-frequency electromagnetic radiation.

(22) An example mechanical load distribution structure 300 is shown separately to the panel in FIG. 3 and then as part of a panel in FIG. 4, which is a cutaway perspective view of the radiation shielding panel. The mechanical load distribution structure 300 is made from sheet steel.

(23) The mechanical load distribution structure comprises a number of holes 302. These holes allow resin to pass through the mechanical load distribution structure into adjacent layers. The mechanical load distribution structure also comprises features 304. The purpose of features 304 will be described below in relation to an x-ray cabinet as shown in FIG. 5. The aggregate of barite covers the mechanical load distribution structure such that the features oldie mechanical load distribution structure are covered. This can be seen in FIG. 4.

(24) An x-ray cabinet for holding an x-ray source can be formed from a plurality of panels of this type. This is shown in FIG. 5. The radiation shielding panels 100 form the walls, roof and floor of the cabinet. An x-ray source 502, which is part of an x-ray inspection system, is shown within the cabinet 500. The x-ray source is part of a system and apparatus for inspecting electronics, such as the Dage Quadra range available from http://www.nordson.com/en/divisions/dage/x-ray-inspection.

(25) Five of the sides of the cabinet are made of single x-ray radiation shielding panels 100. The front face of the cabinet 500 has a door arrangement which comprises two x-ray radiation shielding panels 504 and 505. The panels 504 and 505 have a different size and shape to the other five x-ray radiation shielding panels. The two panels 504 and 505 are attached to different side panels using hinges 508 attached to the respective panels. Panel 504 has a lip which interlocks with panel 505 when the doors close. A labyrinth seal is formed between the two panels when the doors are closed. The cabinet shown in FIG. 5 has external casing elements on some of the panels. For example, casing 510 is shown on top of the top panel 100. The external casing covers the wiring and other electronics required for the control of the x-ray inspection system.

(26) X-ray radiation shielding panels 100 can be manufactured to have features which aid the assembly and improve the construction of the cabinet. X-ray radiation shielding panels used to construct the cabinet may be manufactured with a lip on their outside edges. The lips of adjacent panels at right angles interlock. FIG. 6 shows a cross-sectional schematic view of two panels with lips 602 and 604 interlocking. This interlocking forms a labyrinth seal. The labyrinth seal prevents any line of sight radiation paths between the two panels or radiation paths through lower quantities of radiation attenuating material.

(27) The individual panels 100 that form the sides of the cabinet and the two door parts are held together using fasteners. These fasteners are connected to the panel after the panel has been manufactured. The fasteners are used to hold the various x-ray radiations shielding panels 100 of the cabinet together in an interlocking relationship, and include features such as the door hinges for panels 504 and 505.

(28) Fasteners needing to withstand low loads, such as fasteners holding two adjacent sides of the cabinet together, can connect to any of the resin permeated layers of the x-ray radiation shielding panel. However, some connections, such as hinges, need to withstand higher loads. X-ray radiation shielding panels 100 comprising a mechanical load distribution structure, as shown in FIGS. 3 and 4, allow for connection of fasteners that need to withstand higher loads. The mechanical load distribution structure provides a strong point of contact and distributes the load. This allows for a strong and robust connection to be made between the x-ray radiation shielding and fastener. An example of such a fastener is a hinge, such as the hinge 508 of FIG. 5. The hinge is attached such that it is connected to the mechanical load distribution structure.

(29) The mechanical load distribution structure 300, shown in FIGS. 3 and 4, is shaped to accommodate the type of fasteners required. An example of this is feature 304, which is a fixing point to which hinges can be fixed. The fixing point extends perpendicular to plane of the panel 100. As can be seen in FIG. 4, the fixing point 304 is on the edge of the panel for attachment of a hinge, such as hinge 508 of FIG. 5. The hinge 508 is attached to the panel 100 through the fixing point 304. External forces caused by anything attached to the hinge, such as a door or door part, is then spread through the mechanical load distribution structure 300 from the fixing point 304.

(30) FIG. 7 illustrates the junction between a sidewall panel and the roof panel of the cabinet of FIG. 5. The two panels have the same lip structure as shown in FIG. 6. Each of the panels comprises a first layer 110, a core layer 102 and a second layer 120. Each first layer extends across the full extent of core layer of both panels. However, the second layer of each panel only extends across apart of each core layer. This allows for the attachment of metal casing structure 510 in a manner that provides for a flush finish. The metal casing structure is fixed to the panels using screw fixings 720. The junction between the two panels thus provides a labyrinth seal, preventing the escape of x-rays, as well as an aesthetically pleasing finish.

(31) In the manufacture of the panel, a mould is used. FIG. 8 is a perspective view with the mould 800 when open and empty. The mould comprises a main body section 802 defining a cavity and a lid 803. The mould also comprises a binder or resin input port 804 and a vacuum port 808. In FIG. 8 the points where the ports interface the mould are not visible. However, a pipe that protrudes from each of the ports is shown. Around the outside of the cavity is a channel 806. The binder or resin port 804 is connected to the channel 806 such that resin exiting the resin input port 804 flows into the channel 806 and around the periphery of the main body section 802. The resin input port 804 and channel 806 are on the opposite side of the mould to the outlet port 808. The outlet port 808 is connected to a vacuum pump 810. The vacuum pump 810 draws air from the vacuum port and so creates a vacuum in the main body section 802 of the mould when turned on.

(32) FIG. 9 is a flow chart showing a method for producing the radiation shielding panel described above.

(33) FIG. 10 is an exploded perspective view of the contents of the mould and the layers that are placed into the mould.

(34) The first step 902 is to treat a mould with a release agent 1002. This aids removal of the radiation shielding panel after it has been moulded. In step 904 a gel coat layer is then applied to the mould.

(35) In step 906 a first Polymat™ Free Flow sheet is placed in the main body section 802 of the mould. The Polymat™ Free Flow sheet 110 comprises three layers. The two outer layers are layers of chopped strand glass fibre The third layer, between the two outer layers, is a resin spreader layer which is a polypropylene needle bonded core. The barite aggregate 104 is then poured into the main body section in step 908, and is spread evenly in the mould. The aggregate of barite 104 is poured to fill the mould to a level higher than the top of the main body section 802 of the mould. In this example it is filled so that the aggregate layer extends to a height of about 10% of the depth of the cavity of the mould above the top of the main body section of the mould.

(36) In step 910 a second Polymat™ Free Flow sheet 120 is placed on top of the barite aggregate, similar to the first Polymat™ Free Flow sheet.

(37) The additional layer of step 912 is not shown in FIG. 10. In this step any additional layers, such as the metal mesh for reflecting electromagnetic radiation or the mechanical load distribution structure 300, are also placed in the main body of the mould. These layers are not, essential for creating a panel capable of absorbing x-rays. They can be placed between any of the other layers already in the mould, or as an external layer, and so step 912 can occur between any of steps 904 to 910. At step 914 a gel coat layer is applied to the top surface of the mould.

(38) In step 916 the mould lid 803 is closed. This compresses the aggregate of barite which, prior to closing, extends above the top of the mould. This compression ensures that the core layer 102 has a high density of barite. This allows the panel to be made as thin as possible which in turn minimises the overall thickness and mass of the radiation shielding panel. Uniform compression using the lid also avoids separation of the larger particles in the aggregate from the smaller ones and helps to ensure a uniform distribution of barite within the mould. Closing the lid 803 of the mould provides a gas tight seal. The process of permeating the contents of the mould with resin can then be initiated.

(39) FIG. 11 shows two cross sectional close up views of portions of the mould after step 916 and so after all the layers have been placed in the mould and it has been closed.

(40) FIG. 11a is a close-up cross-section view of the vacuum outlet port 810 positioned on the opposite side of the main body of the mould to the resin input port 808. An arrow shows the direction of the resin flow, out of the mould. At step 918 the outlet port 808 is opened and vacuum pump 810 is turned on. The vacuum pump 810 evacuates air from the main body of the mould. The vacuum pump 810 applies a pressure of between 50000 and 100000 Pa below atmospheric pressure.

(41) FIG. 11b is a close-up cross-sectional view of the resin input port 804. In step 920 the resin input port 804 is opened, a short time after the outlet port 808 is opened and the vacuum has been switched on. This allows for air in the mould to be evacuated before the resin input port is opened. Resin flows through the input port in the direction shown by the arrow. The resin used is Sicomin™ 8100 resin. At the bottom of the resin input port 804 is the channel 806 into which the resin flows and is spread around the periphery of the main body section of the mould. From the channel 806 the resin passes into the first layer 110. Resin is introduced into the resin input port at a pressure above atmospheric pressure and in the direction shown by the arrow in FIG. 11b. The pressure required is dependent on a number of factors, including mould size, and in this example is selected to maintain a flow rate of 0.2 litres per minute at the resin input port. In this example the panel is 1.2 m by 1 m by 24 mm. A pressure of between 50000 and 400000 Pa is desirable. In this example, a pressure of 50000 Pa above atmospheric pressure is used to complete the process. If the permeation of the resin is too fast it can result in disturbance of the aggregate of barite. The combination of the pressure applied to resin entering the input port 804, pushing the resin into the mould, and the vacuum provided by the vacuum pump 810, pulling the resin toward the vacuum port 808, encourages resin to move from the channel 806 and permeate the components in the main body of the mould 802. The vacuum exerts a force on the lid of the mould such that it is pulled in the direction of the vacuum port. This has the effect of compressing the aggregate of barite further than at step 916 after the closure of the lid of the mould. Compressing the barite ensures that the core layer is uniform and dense.

(42) There are two directions of permeation of the resin that are important. The first direction is horizontally across the mould. The second direction is vertically through the mould in the general direction from the resin input port 804 and channel 806 toward the outlet port 808. This second direction of permeation results in resin passing from a higher layer or component in the main body of the mould 802 to a lower layer or component that is closer to the outlet port 808.

(43) After step 920 the process of permeating the contents of the mould with resin is terminated. The process is only terminated after the contents of the mould has been completely permeated with resin. When the resin has completely permeated the panel vertically it will reach the outlet port to which the vacuum pump 810 is connected. The pump is switched off several minutes after the resin comes into contact with outlet port 808. This delay ensures that all air is evacuated from the mould. Resin should be prevented from entering the vacuum pump 810 during this time as it would cause damage to the pump. Entry of resin into the port can be prevented using a fine mesh on the outlet port 808 or by placing additional layers between the outlet port 808 and the constituent parts of the x-ray radiation shielding panel in the mould. Alternatively, resin can be allowed to permeate into the line connecting the mould to the vacuum pump 810, the line is shown as 812 of FIG. 8. A catchpot can be placed between the mould and pump to prevent resin entering the pump. The resin input port 804 is closed before stage 922, several minutes before the vacuum pump has been switched off.

(44) It is necessary to balance the permeation in both the vertical and horizontal directions to ensure that the entire radiation shielding panel is fully permeated with resin before step 922 is reached and permeation is terminated. If, for example, the resin spreads vertically too quickly then there may be regions of the mould that the resin will not have reached. Complete permeation is important in order to create a strong radiation shielding panel. Furthermore, any regions of the core layer, comprising the aggregate of barite, that are not completely permeated with resin may settle and compress over the lifetime of the panel. This mays result in voids opening up in the core layer without the presence of the aggregate of barite. These voids would result in radiation pathways with lower radiation attenuation and so mean that leakage of radiation can occur.

(45) At the beginning of the permeation process resin will leave the channel 806 and pass into the Polymat™ 120. The Polymat™ comprises the resin spreader layer. The resin spreader layer allows for fast horizontal permeation of the resin compared to the rate of vertical permeation. In tis example, horizontal permeation is 30 times faster than vertical permeation. This means that by the time the resin reaches the bottom of the resin spreader layer 124 the entire plane of the resin spreader layer 124 is permeated with resin. From this point on the resin will continue to permeate vertically through the various components in the main body of the mould 902 and horizontal permeation will cease. This avoids disturbance of the aggregate as the resin permeates through the layers subsequent to the Polymat™.

(46) At step 924 the mould is heated to 70° C. warming the Sicomin™ 8100 resin to increase the rate of curing. The resin is hardened in this step. Step 926 is a further hardening step in which the mould is post cured in a bakeout oven. The radiation shielding panel is then fully formed and can be removed from the mould. Fasteners can be attached to the finished panel, as described above, after it has been removed from the mould. A plurality of panels can be manufactured, having different shapes. These can be fitted together to form a cabinet, such as the cabinet of FIG. 5.

(47) The method described with reference to FIG. 9 can be adapted so that a portion of the mould forms a part of the finished radiation shielding panel. If a portion of the mould is not coated with a release agent, the binder may adhere firmly to it and that portion of the mould then forms an external layer of the panel. This may be beneficial in some circumstances. For example, when the panel is to form a door of an x-ray shielding enclosure, having an external layer formed from a sheet of metal provides a convenient structure for attachment of fixings, such as hinges and a door handle.

(48) FIG. 12 is a cross sectional view of the formation of an x-ray shielding panel in which the lower part of the mould forms part of the finished panel. The upper part of the mould is formed from a flexible sheet formed from polythene. The lower part of the mould 1200 is formed from steel and comprises a base plate and side walls. A first layer of Polymat™ 1220 is first placed in the lower portion of the mould. No release agent or binder gel coat is used on the lower portion of the mould. Then the particulate radiation attenuating material 1230, in this case an aggregate of barite, is poured on top of the first layer of Polymat™. A second layer of Polymat™ 1240 is then placed on the barite.

(49) A thin metal sheet 1250 is laid on top of the second layer of Polymat™ 1240. This metal sheet forms part of the finished panel and provides fire retardancy and EMC shielding. The flexible sheet 1210 that forms the top part of the mould is then placed on top of the metal sheet and adhered to the lower portion of the mould using an adhesive so that the interior of the mould is completely sealed between the lower and upper portions of the mould, except for the provision of one or more resin input ports in the flexible sheet and an output port in the lower portion of the mould (not shown).

(50) The output port is then connected to a vacuum pump and the binder input port(s) connected to a resin supply, as in the process described with reference to FIG. 9. The vacuum pump is switched on first. This evacuates air from the mould and sucks the flexible sheet 1210 down against the contents of the mould, compacting the particulate barite and ensuring all portions of the mould are filled. The resin input port is then opened and the resin introduced through the resin input port at atmospheric pressure. The resin is drawn through the mould by the vacuum pump and the permeation process and curing and post-curing steps are then carried out as described with reference to FIG. 9. The flexible sheet 1210 is then removed from the finished panel and discarded.

(51) A panel that can additionally or alternatively shield types of ionizing radiation different to x-rays can be made by adding materials effective at attenuating that type of ionizing radiation to the particulate material. The shielding panel may be made to shield neutron radiation by adding particulate boron nitride to the particulate material in the panel illustrated in FIG. 1, prior to the infusion of the resin. Alternatively, a layer of particulate boron nitride may be added as a separate layer to the barite. The boron nitride layer may be positioned between the barite and one of the Polymat™ layers and preferably, in use the panel is oriented that the boron nitride is positioned on the side of the barite layer closest to the source of neutron radiation.

(52) A panel of this type, that can shield users from neutron radiation, may be used in medical settings and to surround neutron microscopes, for example. It may be desirable to manufacture neutron radiation shielding panel that are larger than the x-ray shielding panels described above. However, the manufacturing process is essentially the same, and the size of the particles or boron nitride is preferably similar to the size of the panicles of barite. To produce a larger panel it may be desirable to reduce the pressure difference across the mould to increase permeation time. Alternatively, multiple resin input ports and/or multiple output ports may be used.