Patent Number: 054421861
Section: summary

FIELD AND BACKGROUND OF THE INVENTION This invention relates to a radioactive isotope source, and more particularly to an encapsulated radioactive isotope source which is designed to permit re-encapsulation and reuse of the radioactive isotope. Various types of analytical instruments use a radioactive isotope source in order to obtain measurements of the physical characteristics or properties of a test specimen. For example, there are commercially available instruments which use a radioactive isotope source for measuring properties such as density, composition, moisture content, thickness, etc. Examples of such test instruments are described in the following United States patents owned by applicants' assignee: U.S. Pat. Nos. 4,525,854; 4,542,472; 4,587,623; 4,766,319; 4,874,950; 4,979,197; and 5,155,356. In nuclear instruments of the general type illustrated by the above patents, the radioactive isotopes are typically contained in a capsule. For example, where the isotopes are americium and beryllium, small pellets of the americium and beryllium are packaged in a stainless steel capsule. Even though the radioactive half-life of these isotopes is very long (e.g. over 400 years) it is often recommended that the instruments be returned to the manufacturer periodically so that the radioactive isotope source can be reconditioned or replaced. This is because the weld in the stainless steel capsule may lose strength or become brittle after a number of years. In the past, used radioactive isotope source capsules were collected and sent to a disposal site for radioactive materials. However, it has become increasingly difficult to find disposal sites which will accept such radioactive materials. SUMMARY OF THE INVENTION The present invention provides a way to re-encapsulate and thus reuse radioactive isotope source capsules. Specifically, in accordance with the present invention a source capsule containing a radioactive isotope is put inside of an outer protective jacket or capsule and the outer jacket is sealed. The outer protective jacket is so designed that it can be reopened without disturbing the radioactive isotope source capsule contained therein. Thus, when it becomes necessary to recondition the source capsule, the inner source capsule can be removed from the outer protective jacket and it can be re-encapsulated in another outer protective jacket. Because of the long radioactive half-life of the isotopes employed, the source capsules can be re-encapsulated as many times as may be needed, thus avoiding the problems associated with disposal of the radioactive isotopes. Furthermore, the ability to reuse the radioactive isotope source allows for recycling and thus an overall reduction in the number of sources produced. In accordance with one embodiment of the present invention, there is provided a re-encapsulated radioactive isotope source which comprises an outer protective jacket in the form of a can having a side wall, an integrally formed bottom wall and an open upper end. A source capsule containing a radioactive isotope is received within this outer protective jacket. A jacket cap is received within the outer protective jacket so as to close the open end of the jacket, with the source capsule thus located within the outer protective jacket. The jacket cap has its outer peripheral edge positioned in close fitting relation to the inner peripheral surface of the jacket side wall to form a narrow gap between the jacket cap and the jacket side wall. A seal, such as a weld, extends along the narrow gap, joining the jacket cap to the jacket and sealing the source capsule within the protective jacket. In a preferred embodiment, the axial length of the jacket is greater than the axial length of the source capsule and a removable spacer is positioned within the jacket filling the space between the source capsule and the jacket cap. A score line is provided on the outside surface of the jacket in the region of the underlying spacer to facilitate reopening the outer jacket without risk of damage to the original source capsule. When it becomes necessary to recondition the source by re-encapsulation, the protective outer jacket is reopened and the original source capsule is removed from the jacket. The source capsule and a new spacer are then positioned within another outer protective jacket in the form of a can having a side wall, an integrally formed bottom wall and an open upper end. Another jacket cap is positioned within the outer protective jacket so as to close the open end of the jacket with the source capsule being located within the jacket. The jacket cap has its outer peripheral edge positioned in close fitting relation to the inner peripheral surface of the jacket side wall to form a narrow gap between the jacket cap and the jacket side wall. A seal is formed extending along the narrow gap to join the jacket cap to the jacket and to seal the source capsule within the protective jacket.