AU732122B2 - Isotope holder - Google Patents

Description

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR OFFICE USE Short Title: Int Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority Related Art: Name of Applicant: Address of Applicant: Actual Inventor: TO BE COMPLETED BY APPLICANT Stephen John Newlands 36 North West Arm Road, GYMEA 2227 AS ABOVE ANDERSON-TAYLOR ASSOCIATES, Registered Patent Attorneys of 10 Harrison Avenue BONNET BAY N.S.W. 2226 Address for Service: Complete Specification for the invention entitled: ISOTOPE HOLDER The following statement is a full description of this invention, including the best method of performing it known to me: -1- This invention relates to radioactive isotope holders.

In many industrial situations such as for example density measurements of mine slurry a radiation beam from a Caesium 137 or Cobalt 60 capsule is directed through the flow pipe and then measured by a detector. The variation in intensity of the beam as it passes through the pipe gives an accurate ongoing measure of the slurry density. Such installations however require the provision of special long term holders for the radiation capsules which are normally left in place for several years. Further, there are rigorous safety standards imposed on the construction of these holders and consequently such apparatus tends to be expensive and complicated to produce.

It is an object of this invention to ameliorate the above disadvantage by providing a simpler and lower cost isotope i. holder which nevertheless complies with all relevant safety and security standards.

o* *o Accordingly there is disclosed a holder for a capsule of a radioactive isotope comprising a casing having an internal recess or compartment for containment of said capsule, said recess or compartment being in radiant communication with the exterior of said casing along a predetermined direction and being insulated in other directions from said exterior by a .ooo barrier of radiation blocking material and a shutter assembly associated with said casing which is movable between a closed -2position whereby emitted radiation from said capsule along said predetermined direction is blocked and a open position whereby said emitted radiation is passed.

The currently preferred form of this invention will now be described with reference to the attached drawings in which: Figure 1 is a perspective side view of one form of isotope holder according to this concept, Figure 2 is a cross-sectional view along the lines A-A of figure 1i, and Figure 3 is a plan view of the isotope holder of figure 1.

Referring first to figure 1 there is shown a cylindrical casing 1 of mild steel with a planar top 2 carrying a radiation name plate 3. The casing is welded onto a shutter housing 4 which may comprise a standard length of rectangular steel stock of 5 mm wall thickness. There are flanges welded to each side for mounting the holder and a lock 6, pin 7 and on/off indicator 8 on the top of the housing as described later in more detail. Although the invention is not restricted to any particular size or type of isotope capsule, with the particular holder shown in this embodiment a capsule of 3.7 gigabecquerels can be contained.

As shown in more detail by figure 2 the casing 1 comprises a circular steel wall 9 which together with the top plate 2 and bottom plate 10 encloses a radiation insulating material 11 of for example lead. This lead in turn surrounds a central steel walled compartment 12 for containment of a capsule 13 of Caesium 137 or Cobalt 60. Although the invention is not restricted to any particular method for holding the capsule with this example there is a steel source rod 14 which extends up from a circular flange 15 at the base of the casing 1 into the compartment 12. The capsule 13 is secured to the top of the source rod 14 by an axial grub screw 16.

Screws 17 are also used to hold the flange 15 up against the base of the casing 1 and thereby fix the source rod and capsule assembly within the compartment 12. As required by the relevant safety codes the radiation barrier 11 surrounding the compartment 12 is of sufficient thickness and mass to reduce the doserates from the holder to less than 500 microsieverts at the outside surface and less than microsieverts at a distance of 1 metre from the holder.

The walls of the casing are preferably of welded steel construction and the lead radiation barrier 11 is poured into the cavity around the central compartment prior to attachment of the top plate 2. An air gap 18 of about 3 mm is preferably left between the upper surface of the lead mass and top plate for expansion purposes in the event that the housing is •subjected to high temperature.

The lower section of the compartment 12 as shown in figure 2 opens through an aperture in the bottom plate 10 and -4insulation barrier 11 to enable a directed beam of radiation to emanate out of the casing. To selectively control the release of this radiation the shutter housing 4 is welded to the bottom of the casing 1. As best shown in figure 3 there is within the housing 4 a lever arm 19 pivotably mounted on the pin 7 referred to earlier. The outer end 20 of this lever may be moved manually by an operator between the "on" and "off" positions using the indicator 8 also referred to earlier. At the "off" position the lever arm abuts a stop pin 21 and a mass 22 of lead or other radiation blocking material at the inner end is positioned directly across the lower section of compartment 12 to prevent radiation emanating from the capsule 13. At the "on" position this mass 22 is turned clear to one side of compartment 12 so that the beam radiates out through a bottom opening 23 in the shutter housing without obstruction. Preferably the mass 22 is contained within a steel shell 24 and an air gap 25 is also provided above the mass 22 to allow for expansion at high temperatures as with the casing 1.

For security a key operated cam lock 6 is provided in the top of the shutter housing adjacent the lever 20. A cam 26 (see figure 3) attached to this lock 6 can thus be turned to the direction shown where it holds the lever in the "off" ego*o position against unauthorised tampering. A second pin 27 may also be provided which is placed in either of two holes 28 or 29 where it extends through the top of the housing to hold the lever arm 20 in either the "on" or "off" position.

It will thus be appreciated that this invention at least in the form of the embodiment disclosed comprises a novel and useful improvement in isotope holders. Clearly however the example described is only the currently preferred form of this invention and a wide variety of modifications may be made which would be apparent to a person skilled in the art.

For example the shape and configuration of the casing for the capsule and the shutter housing may be changed according to design preference. The invention is also not limited to any particular materials of construction although mild steel is preferred for the walls and moving parts of the holder and lead for the radiation barriers.

For the purposes of this specification expressions such as "bottom", "upper" and "lower" refer to the device in one possible position of use as illustrated and are not to be read as necessarily limiting.

*o oooeo

Claims (5)

1. 2. The holder as claimed in claim 1 wherein said shutter assembly is mounted in a housing which is secured to said casing so that when said shutter assembly is at said open *o*position said emitted radiation passes through said housing.
2. 3. The holder as claimed in claim 2 wherein in use of said holder the capsule is secured to the end of a source rod which extends into said compartment from the exterior of said casing.
3. 4. The holder as claimed in claim 3 wherein the casing -7- comprises a cylindrical side wall and top and bottom plates. The holder as claimed in claim 4 wherein there is an air gap between an upper surface of said barrier of radiation blocking material and said top plate to allow for expansion at elevated temperatures.
4. 6. The holder as claimed in claim 5 wherein there is an air gap between an upper surface of said mass of radiation blocking material and an upper wall of said steel shell to allow for expansion at elevated temperatures.
5. 7. The holder as claimed in claim 6 wherein said radiation blocking material is lead. A holder for a capsule of a radioactive isotope, said holder being substantially as described herein with reference oto the drawings. Dated this 23rd day of January 2001 Stephen John Newlands By his Patent Attorney MICHAEL ANDERSON-TAYLOR