Patent Number: 054421861
Section: description

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring now more particularly to the drawings, a re-encapsulated radioactive isotope source is indicated generally in FIG. 1 by the reference character 10. The source 10 includes an outer protective jacket 11 which is preferably made of a metal, such as stainless steel. As shown more fully in FIG. 3, the protective jacket 11 is in the form of a cylindrical can and includes a cylindrical side wall 11a and an integrally formed bottom wall 11b. As seen from FIGS. 2 and 3, a cylindrical source capsule 12 is positioned within the outer jacket 11. The source capsule 12 is of a cylindrical configuration of a diameter only slightly smaller than the inside diameter of the jacket 11 so that it readily fits within the protective jacket. The capsule 12 includes a cylindrical can-shaped outer shell including a cylindrical side wall 12a, an integrally formed bottom wall 12b and a lid or cap 12c joined to the side wall by a weld 12d. A radioactive isotope 13 is sealed within the capsule. The bottom wall 12b of the capsule abuts the inner surface of the bottom wall 11b of the protective jacket and at the opposite end the cap 12c of the capsule faces the open end of the jacket. Overlying the source capsule 12 is a spacer plug 14. In the embodiment illustrated, the spacer plug is of a cylindrical configuration, with a diameter just slightly smaller than the inner diameter of the jacket so that outer peripheral surface 14a of the spacer plug is positioned in close fitting relation to the inner peripheral surface of the cylindrical side wall 11a. The spacer 14 has a hole 14b extending axially therethrough which may be threaded to facilitate removal of the spacer. Preferably, the spacer is made of a relatively high-melting material, such as ceramic or refractory, so that it will be unaffected by welding and will remain readily removable from the jacket 11. The re-encapsulated radioactive isotope source 10 is capped and sealed by a cylindrical jacket cap 16. The jacket cap 16 is preferably formed of the same metallic material as the outer protective jacket 11 and has an outside diameter substantially corresponding to the inside diameter of the outer jacket. Thus, the outer circumferential surface 16a of the jacket cap is positioned in opposing, closely fitting relation to the inner peripheral surface of the jacket side wall 11a, with a narrow annular gap 17 being formed therebetween. A seal 18 overlies the annular gap 17 and forms an airtight, watertight closure, thus securing the jacket cap 16 to the jacket 11. The seal 18 is preferably formed by a weld, although other sealing methods such as brazing, epoxy, adhesives, etc. could be suitably employed. The outward facing surface of the jacket cap 16 has a raised perimeter portion 16b with a planar surface and a recessed outward facing central portion 16c surrounded by the perimeter portion 16b. The raised perimeter portion 16b of the cap and the endmost facing edge portion 21 of the cylindrical side wall 11a defines surfaces which are in substantial alignment with each other and collectively form a raised annular shoulder at one end of the source 10. To facilitate obtaining a good strong weld and an effective seal, it is preferred that there be a V-shaped recess along the annular gap 17 to receive the weld. Thus, as best seen in FIG. 3, the juncture between the exposed outward facing surface of 16a of the jacket cap and the adjoining outer peripheral edge surface of the raised portion 16b forms a chamfered corner. Similarly, the juncture between the exposed endmost surface 21 of the jacket side wall 11a and the adjoining inner peripheral surface 11c of the side wall also forms a chamfered corner. Once the encapsulated radioactive isotope source 10 has served its expected service life, it can be readily reconditioned by reopening the sealed re-encapsulating jacket, removing the existing source capsule 12 and by re-encapsulating it in a new outer protective jacket 11, with a new spacer plug 14 and a new jacket end cap 16 and a new weld 18. To facilitate reopening the jacket, a score line 29 is formed on the exterior of the cylindrical side wall 11a of the jacket at a location opposite the underlying spacer plug 14. A tubing cutter can be used to sever the side wall 11a along the score line 29. The presence of the spacer plug 14 assures that the cutting of the jacket 11 does not affect the source capsule 12. The cap 16 and the spacer plug 14 can thereupon be removed from the jacket 11 allowing the source capsule 12 to be removed. The threaded hole in the spacer can be used to facilitate removal of the spacer from the jacket. The source capsule 12 can then be re-encapsulated by placing in another outer protective jacket as previously described.