Radiation source container

Abstract

A source container for a radiation source includes a vessel having an external wall defining a space within which is located a shield formed from a radiation absorbing material and defining a cavity for receiving a radiation source, the shield including a window extending from the cavity through the radiation absorbing material, and at least two shutters, each shutter being movable between a closed position in which the shutter covers the window and an open position in which the shutter does not cover the window. The provision of two or more shutters provides a way to emit radiation of different intensities from the same source and container.

Claims

1. A source container for a source of ionizing radiation for a measuring instrument or measuring system, the source container comprising: a vessel having an external wall defining a space within which is located a shield formed from a radiation absorbing material, said shield defining a cavity for receiving a source of ionizing radiation, a single transmission window extending from said cavity through said radiation absorbing material and to the external wall, and at least two shutters positioned in line with the single transmission window, each shutter being capable of preventing transmission of at least some radiation emitted by said source through the shutter, each shutter being movable between a closed position in which said shutter covers said transmission window and an open position in which said shutter does not cover said transmission window, and said shutters being operable to produce an operational condition in which all of the at least two shutters are closed, all of the at least two shutters are open, or at least one shutter is closed and at least one shutter is open, wherein a minimum amount of radiation is transmitted or emitted from the container through the transmission window when all of the at least two shutters are closed; a maximum amount of radiation is transmitted or emitted from the container through the transmission window when all of the at least two shutters are open; and an amount of radiation which is intermediate between the minimum and maximum amounts is transmitted or emitted from the container through the transmission window when at least one shutter is closed and at least one shutter is open.

2. The source container as claimed in claim 1, wherein the source is a source of gamma radiation, X-rays, beta particles or neutrons.

3. The source container as claimed in claim 1, wherein the source is >about 10 Ci (370 GBq).

4. The source container as claimed in claim 1, wherein the external wall of the container is formed from steel or aluminium.

5. The source container as claimed in claim 1, wherein the at least two shutters are movable between the open and closed positions by sliding, hinging, folding or rotating.

6. The source container as claimed in claim 1, wherein the at least two shutters engage with parts of the shield surrounding the window by means of at least one channel along which the shutter may be moved between open and closed positions.

7. The source container as claimed in claim 1, wherein the movement of at least one shutter between open and closed positions is controlled by a motor.

8. The source container as claimed in claim 1, wherein the movement of the at least two shutters between open and closed positions is controlled by a spring, a lever or a cam.

9. The source container as claimed in claim 1, wherein the at least two shutters are biased towards the closed position.

10. The source container as claimed in claim 1, wherein the movement of at least one shutter between open and closed positions is operable remotely.

11. The source container as claimed in claim 1, further comprising an interlock to control the movement of the at least two shutters between open and closed positions.

12. The source container as claimed in claim 1, wherein the movement of each of the at least two shutters between open and closed positions is controlled by a spring and each of the at least two shutters are biased towards the closed position, and wherein the movement of the at least two shutters between the open and closed positions occurs by sliding in an axial direction with respect to container.

13. A method of measuring a property of an object with a nucleonic instrument, said instrument comprising a source of ionising radiation and one or more radiation detectors capable of detecting said ionising radiation, wherein the source and detector(s) are arranged such that radiation from the source is caused to interact with the object and the radiation detectors are caused to detect said radiation after it has interacted with the object; and wherein said source is located within the source container as claimed in claim 1.

14. The method as claimed in claim 13, wherein said instrument is subjected to a calibration operation and at least one of the shutters is closed and at least one of the shutters is open during said calibration operation.

15. The method as claimed in claim 14, wherein said instrument is operated to perform the measuring of the property of the object and wherein more of said shutters are in the open position during said measuring operation than during said calibration operation.

16. The method as claimed in claim 13, wherein the source is a source of gamma radiation, X-rays, beta particles or neutrons.

Description

(1) An embodiment of the invention will be further described with reference to the accompanying drawings.

(2) FIG. 1 is a schematic view of a source container.

(3) FIG. 2 shows a transverse section through a source container of the invention.

(4) FIGS. 3-5 each show a longitudinal section through a source container of the invention.

(5) FIG. 1 shows a radiation source container 10 according to the invention. In this embodiment, the container is cylindrical and has an external shell 12 made from aluminium. The cover 14 of the source holder 16 is located at one end of the container. FIG. 2 is a representation of a section through the container along line A. The source holder 16 is located approximately centrally within the container. Shielding material 18, formed from a radiation-absorbing heavy alloy, is positioned between the source holder and the external shell. A primary shutter 20 and a secondary shutter 22, also of heavy alloy, are arranged to cover and close an opening 24 in the shielding 18. The shutters 20, 22 are arranged to be movable in the direction of the axis of the cylindrical container and are provided with tongues 26 which are sized and positioned to engage with channels 28 formed in the shield 18, thereby to guide movement of the shutters relative to the shield.

(6) FIGS. 3-5 show a representation of a longitudinal section through the cylindrical container 10. The source is mounted at the end of rod 16, which is secured in place by threads (not shown) engaging a channel through the end wall of the shell. O ring 40 prevents fluid from entering into the container through the opening into which the rod 16 is secured. The cover, or cap, 14 is secured over the end of rod 16 by means of screws (not shown) and an O ring 38 further protects from fluids which may otherwise enter the container between the cap and the end wall. In FIG. 3, both shutters 20, 22 are closed and cover the opening 24 in the shielding material. In this position the maximum amount of radiation from the source 30 is absorbed by the shutters. The shutters may be operated by means of shafts 32, 34 and are biased to their closed position by compression springs 36. FIG. 4 shows the container with the primary shutter open and the secondary shutter closed. In this configuration, some radiation emitted by source 30 is absorbed by shutter 22 whilst a proportion of the radiation is transmitted from the container along opening 24. The relative proportions of the shutters are designed such that the amount of radiation leaving the container in this configuration is sufficient for a particular purpose, such as a calibration operation. In FIG. 5, the container is shown with both shutters open so that the maximum amount of radiation is transmitted from container 10. This configuration may be used when the source is used in the operation for which it is designed, such as in a measuring operation requiring the maximum penetration of the radiation.