Patent Number: 
Section: claims

1. A radiation-shielding assembly for radioactive material, the assembly comprising:a body having a cavity defined therein for receiving radioactive material, the body having first and second openings into the cavity, the first opening being sized smaller than the second opening, and the body being constructed to limit escape of radiation from the cavity through the body;a first base releasably attachable to the body generally at the second opening thereof; anda second base releasably attachable to the body generally at the second opening thereof when the first base is not releasably attached to the body, wherein the first base has a length and a weight, and wherein the second base has at least one of a shorter length and a lighter weight than the first base;the first base including first and second closure surfaces, wherein the first base is releasably attachable to the body in a first orientation in which the first closure surface is positioned generally at the second opening and faces inward of the cavity at a first distance from the first opening, and wherein the first base is releasably attachable to the body in a second orientation in which the second closure surface is positioned generally at the second opening and faces inward of the cavity at a second distance from the first opening, the first distance being different from the second distance. 2. The assembly of claim 1, wherein the body and first base together have a first center of gravity when the first base is releasably attached to the body, wherein the body and second base together have a second center of gravity when the second base is releasably attached to the body, and wherein the first center of gravity is closer to the first opening than the second center of gravity. 3. The assembly of claim 1, wherein the first base comprises:a radiation shield adapted to limit passage of radiation therethrough and positioned generally at the second opening when the first base is releasably attached to the body; andan extension element connected to the radiation shield and configured to extend away from the body when the first base is attached thereto. 4. The assembly of claim 3, wherein the extension element is constructed of a material that is substantially transparent to radiation. 5. The assembly of claim 1, wherein the first base comprises an extension element having first and second spaced apart ends, a first radiation shield connected to the first end of the extension element and adapted to limit escape of radiation from the cavity through the second opening when the first base is attached to the body in the first orientation, and a second radiation shield connected to the second end of the extension element and adapted to limit escape of radiation from the cavity through the second opening when the first base is connected to the body in the second orientation. 6. The assembly of claim 5, wherein the extension element is substantially transparent to radiation. 7. The assembly of claim 5, wherein the extension element and body are constructed of different materials, the material of the extension element being less dense than the material of the body. 8. The assembly of claim 1, wherein the second base comprises first and second closure surfaces, wherein the second base is releasably attachable to the body in a first orientation relative to the body in which the first closure surface is positioned generally at the second opening and faces inward of the cavity at a first distance from the first opening, and wherein the second base is releasably attachable to the body in a second orientation relative to the body in which the second closure surface is positioned generally at the second opening and faces inward of the cavity at a second distance from the first opening, the first distance being different from the second distance. 9. The assembly of claim 8, wherein the second base comprises a single radiation shield. 10. The assembly of claim 8, wherein the second base is constructed for threaded attachment to the body in the first and second orientations. 11. The assembly of claim 1, further comprising:a cap constructed for releasable engagement with the body generally at the first opening thereof. 12. The assembly of claim 1, wherein at least one of the body, the first base, and the second base comprises tungsten-impregnated plastic. 13. The assembly of claim 1, wherein at least one of the first and second bases is constructed to limit escape of radiation from the cavity through the second opening of the body when the respective base is attached to the body. 14. The assembly of claim 1 in combination with the container of radioactive material. 15. A radiation-shielding assembly for radioactive material, the assembly comprising:a body having a cavity defined therein for receiving radioactive material, the body having first and second openings into the cavity, the first opening being sized smaller than the second opening, and the body being constructed to limit escape of radiation from the cavity through the body;a first base releasably attachable to the body generally at the second opening thereof; anda second base releasably attachable to the body generally at the second opening thereof when the first base is not releasably attached to the body, wherein the first base has a length and a weight, and wherein the second base has at least one of a shorter length and a lighter weight than the first base;the second base including first and second closure surfaces, wherein the second base is releasably attachable to the body in a first orientation relative to the body in which the first closure surface is positioned generally at the second opening and faces inward of the cavity at a first distance from the first opening, and wherein the second base is releasably attachable to the body in a second orientation relative to the body in which the second closure surface is positioned generally at the second opening and faces inward of the cavity at a second distance from the first opening, the first distance being different from the second distance. 16. The assembly of claim 15, wherein the second base comprises a single radiation shield. 17. The assembly of claim 15, wherein the second base is constructed for threaded attachment to the body in the first and second orientations. 18. The assembly of claim 15, further comprising:a cap constructed for releasable engagement with the body generally at the first opening thereof. 19. The assembly of claim 15, wherein at least one of the first and second bases is constructed to limit escape of radiation from the cavity through the second opening of the body when the respective base is attached to the body. 20. The assembly of claim 15 in combination with the container of radioactive material. 21. A radiation-shielding assembly for radioactive material, the assembly comprising:a body having a cavity defined therein for receiving a first container of radioactive material, the body having first and second openings into the cavity, the first opening being sized smaller than the second opening, and the body being constructed to limit escape of radiation from the cavity through the body;a first base releasably attachable to the body generally at the second opening thereof; anda second base releasably attachable to the body generally at the second opening thereof when the first base is not releasably attached to the body, wherein the first base has a length, and wherein the second base has a shorter length than the first base to accommodate a second container;the body and first base together having a first center of gravity when the first base is releasably attached to the body, the body and second base together having a second center of gravity when the second base is releasably attached to the body, and wherein the first center of gravity is closer to the first opening than the second center of gravity. 22. The assembly of claim 21 in combination with the container of radioactive material.