BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front isometric view of a prior art radiation source device.
FIG. 2 is a front view of the prior art radiation source device of FIG. 1.
FIG. 3 is a cross-sectional view of the prior art radiation source device of FIG. 2 through view lines 3-3.
FIG. 4 is a front isometric view of an exemplary embodiment of a radiation source device of the invention.
FIG. 5 is a cross-sectional view of the exemplary embodiment of the assembled radiation source device of FIG. 4.
FIG. 6 is an exploded view of the exemplary embodiment of a radiation source device of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a front isometric view of a prior art radiation source device 10, shown as a generally cylindrical device. A front view of the radiation source device 10 is shown in FIG. 2 and a cross-sectional view along view lines 3-3 of FIG. 2 is shown in FIG. 3. The radiation source device 10 has a capsule portion 12 with an open front 14. The capsule is preferably made of a strong and radiopaque material, such as stainless steel, nickel-copper alloys, such as Monel®, etc. The open front 14 has an outer rim 16 with an inner seating rim 18. The capsule has an outer cylindrical surface 20 and an inner cylindrical surface 22 that defines a generally cylindrical space therein. The inner seating rim 18 projects inwardly of the inner cylindrical surface 22. A section of radiolucent material, such as a section of beryllium is used to form a radiolucent window 24, which is sized to tightly fit behind the inner seating rim 18. The beryllium window is permanently affixed in place, e.g., by brazing. A generally cylindrical plug 30 is provided that has an outer diameter that is sized to fit within the space of the capsule 12 snuggly against the inner cylindrical surface 22. The plug 30 is preferably made of a strong and radiopaque material such as stainless steel, nickel copper alloys and the like, and has a recess 32 that is sized to receive a radioactive element 34. The plug 30 with its carried radioactive element 34 is inserted into the capsule with the radioactive element 34 seated against the inside of the radiolucent window 24, so that radiation emanates from the radiolucent window 24, but not from other directions of the radiation source device 10. The plug 30 is preferably permanently affixed to the capsule 12, e.g., by fusion welding 36.
It is desirable to provide a radiation source device a small size format, and accordingly, it is desirable to be able to size radiation source devices as small as possible. For example, prior art devices have been sized to be relatively small, such as having a diameter of about 8 mm, with a window size of about 5 mm. However, properly brazing the beryllium window 24 to the capsule 22 in these small size formats becomes difficult and there can be a high defect rate. Accordingly, the design of prior art radiation source devices is not ideal.
FIG. 4 is a front isometric view of an exemplary embodiment of a radiation source device 50 of the invention, FIG. 5 is a cross-sectional view of the assembled radiation source device of FIG. 4 along view lines 5-5 of FIG. 4, and FIG. 6 is an exploded view of the radiation source device 50 of FIG. 4. The radiation source device 50 comprises a capsule 52 made of a radiopaque material, such as stainless steel, nickel copper alloys and the like. The capsule 52 can have a generally cylindrical shape with a closed end 54 and an open end 56 defining a cavity 58 therein. The open end 56 has a seating rim 60. The capsule 52 has an inner diameter “Di” at the open end and has an outer diameter “Do”, with the inside surface 62 of a cylindrical wall portion 64 defining the inner diameter “Di” and an outer surface 66 defining the outer diameter “Do”. A primary element 70, for example as a section of cylindrical wire 72 formed of a metal such as stainless steel, copper, nickel, silver, etc., or other suitable materials, such as porous ceramic, porous glass, and ion exchange resin beads, and has a predetermined diameter Da and predetermined length, and has a flat front end 74. A radioactive part 76, such as a thin section of radioactive foil, is located on the flat front end 74 of the primary element 70. The flat front end 74 of the primary element can also be electroplated with radioactive material 76. Regardless of how the radioactivity is located at the front of the element, the radioactive element can comprise a radioactive isotope, such as the following: 109Cd, 55Fe, 241Am, 57Co, and 133Ba. The primary element 70 is sized to be fit in the cavity 54 of the capsule 52 with its radioactive end 76 facing outwardly towards the open end 56 of the capsule 52. As can be seen, the diameter “Da” of the active element 70 is smaller than the inner diameter Di of the space 58 of the capsule 52. The amount and type of radioactive material is to be selected based on the particular needs of the radiation source material. A radiolucent window portion 80, such as formed by beryllium, is provided. The radiolucent window portion 80 preferably has a flat front face 82 and has a generally cylindrical sleeve portion 84 extending rearwardly from the flat front face 82 to define a window portion cavity 86. The cylindrical sleeve portion 84 has an outer peripheral surface 88 and an inner peripheral surface 90. Behind the flat front face 82, the window portion 80 also preferably provides a generally flat rear surface 92. The window portion 80 preferably has a perimeter rim portion 94 with a surface that is adapted to seat against the seating rim 60 of the open end 56 of the capsule 52 when the window portion 80 is inserted into the open end 56 of the capsule 52. A primary seal 96 is formed in the vicinity of the contact area between the surface of the perimeter rim portion 94 and the seating rim 60 of the open end 56 of the capsule 52. This secondary seal 98 can be formed by adhesive and/or welding. Also, if desired, adhesive can be applied between the outside surface 88 of the sleeve portion 84 and the inner surface 62 of the walls 64 of the capsule 52 to further retain the window portion 70 together with the capsule 52. The cylindrical sleeve portion 84 is sized to be received in the open end 56 of the capsule 52. The outer diameter Dwo of 5 the cylindrical sleeve portion 84 is sized to fit within the inner diameter Di of the inside wall 62 of the cavity 58 of the capsule 52, and the cylindrical sleeve portion 84 has an inner diameter Dwi that is sized to permit the primary element 70 to fit in the window portion cavity 86 such that the radioactive flat end 76 of the primary element 70 will seat adjacent to the flat rear surface 92 of the window portion 80. A primary seal 96, such as formed by an adhesive, e.g., an epoxy resin adhesive, is preferably used to retain the primary element 70 together with the window portion 80. For purposes of meeting governmental regulations, the outer surface 66 of the capsule 52 can bear marking 100 (e.g., “NUCLIDE ACTIVITY”), such as by engraving, to identify the radioactive source device 50 as being radioactive.
Assembly of the radiation source device 50 can take place in a negative pressure glove box, where, for example, the primary element 70 is inserted into the window portion 80 with its radioactive end 76 being seated against the inside surface 92 of the window, and with adhesive used to form the primary seal 98 between the primary element 70 and the window portion 80 to retain these portions together. Thereafter, the primary element 70 and the window portion 80 unit are fitted into the open end 56 of the capsule 52. As noted above, a snug fit will be formed between the outside surface 88 of the window portion 80 adhered with its radioactive end 76 against the flat rear surface 92 of the window portion 80. As noted above, an adhesive (such as epoxy resin) can be used to adhere the window portion 80 to the capsule 50 with the radioactive primary element 70 contained therewithin. Lastly, at the location of the secondary seal 96, further bonding may be effected, such as by adhesive and/or by welding. While welding (fusion welding, laser welding, etc.) can be used, in order to eliminate any beryllium fumes, assembly without the use of welding is desirable, and adhesives are preferable. Indeed, since welding can be eliminated, very small sized radioactive source devices can be made. For example, sources with windows as thin as 0.25 mm (or thinner) and having an diameter of about 3 mm and length of 6 mm or so can readily made with high yields and very low defect rates.
While the exemplary radioactive source device 50 of the invention is shown as have a generally elongate cylindrical shape, radioactive source device of the invention can have other shapes if desired. For example, rather than being cylindrical, the radioactive source device can be frustoconical in shape, can have a polygonal cross-section, etc.
Although embodiments of the present invention have been described in detail hereinabove in connection with certain exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary is intended to cover various modifications and/or equivalent arrangements included within the spirit and scope of the present invention.
Patent Application
20080004482
