GB2281812A

GB2281812A - The processing of materials by means of ionising radiation

Info

Publication number: GB2281812A
Application number: GB9318947A
Authority: GB
Inventors: Mark Nightingale
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1993-09-14
Filing date: 1993-09-14
Publication date: 1995-03-15
Also published as: GB9318947D0

Abstract

A method of processing materials in which a material to be processed is subjected to irradiation with a beam of X-rays having an energy less than 1 MeV. A suitable form of continuously operating X-ray source is described together with a mobile plant for decontaminating contaminated soil, water or sludge. The figure shows a dual source enclosed in an evacuated chamber 1. Each source comprises an RC-excited multipole source 2, an accelerator 4, a de-focusing magnet 5, a target 7 to produce X-rays and a vacuum window 8 combined together in the form of gold or tungsten laminated on aluminium, and a beam deflection magnet 6 which prevents X-rays impinging on the electron accelerator. <IMAGE>

Description

The Processina of Materials bv Means of Ionisinq Radiation The present invention relates to the processing of materials by means of ionising radiation, and more specifically to the treatment of materials to remove toxic substances from them.

It is known that materials which have surface contaminants can be decontaminated by means of ionising radiation. Such a process is disclosed in US Patent 4,382,806, using electron beams of more than 10,000 watts beam power, or gamma rays. However, electron beams have extremely short ranges in anything other than vacuum conditions, and gamma radiation requires considerable biological shielding. Both these techniques, therefore, are unsuitable for use in field conditions by portable plant. The same is true in the case of other proposed systems in which pulsed X-rays of energies greater than 10 MeV are used.

It is an object of the invention in one aspect to provide a continuously operating X-ray source adapted to produce X-rays having an energy of about 1 MeV or less which is suitable for use in the processing of materials.

The use of X-rays having an energy of < 1 MeV prevents the activation of processed material and reduces weight of X-ray shielding required to a level applicable for a mobile treatment plant. It is an object of the invention in another aspect to provide a method of, and apparatus for, the decontamination of materials which is capable of being used under field conditions.

According to the invention in one aspect there is provided a continuously operating X-ray source comprising an evacuated chamber including a volume plasma ion source adapted to produce a beam of electrons, an accelerator adapted to accelerate the electrons to a desired energy, a de-focusing magnet, a target adapted to produce X-rays of a pre-determined maximum energy as a result of bombardment by the beam of electrons, and means for preventing X-rays from impinging on the electronaccelerator.

Preferably the electrons have an energy of less than 1 MeV, typically about 300 KeV and the target consists of a metal such as gold or tungsten bonded to an aluminium alloy vacuum window.

According to the invention in another aspect there is provided a method of processing a material comprising the operations of subjecting a layer of the material to irradiation by X-rays having an energy of less than 1 MeV.

According to the invention in a third aspect there is provided an apparatus for decontaminating a surface, comprising a vehicle which can be moved over a region of a contaminated surface, the vehicle including a power supply, a continuously operating source of X-rays having an energy less than approximately 1 MeV, means for removing contaminated material from the surface, means for transporting the contaminated material to a treatment station where it is subjected to the X-rays and means for delivering decontaminated material to a disposal point.

The means for removing contaminated material from the surface can comprise a scraper and the means for transporting the contaminated material to the treatment station can comprise a conveyor belt system which can be the means for delivering decontaminated material to the disposal point also.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which, Figure 1 is a diagrammatic representation of an Xray source embodying the invention.

Figure 2 is a diagrammatic representation of a mobile treatment source embodying the invention, and Figure 3 is a diagrammatic representation of a dual X-ray source for use in the embodiment of Figure 2.

Referring to Figure 1 of the drawings, a continuously operating source of X-rays consists of an evacuated chamber 1, which also is adapted to provide biological shielding from X-rays, within which there are disposed an RF-excited multipole ion source 2 adapted to produce a beam of electrons 3, a DC electron accelerator 4, a de-focusing magnet 5, a beam-deflecting magnet 6, an X-ray target 7 and a vacuum window 8. The electron beam source 2 is adapted to produce an electron beam having a beam current of up to about l.2A and the electron accelerator 4 is adapted to accelerate the electrons to a beam energy of up to 1 MeV. The X-ray target 7 and the vacuum window 8 are combined together in the form of a laminate of heavy metal such as gold or tungsten bonded to a sheet of aluminium. The purpose of the beam deflecting magnet 6 is to prevent the inadvertent illumination of the structure of the electron accelerator 4 by X-rays.

Referring to Figure 2, a mobile plant for the treatment of decontaminated soil consists of a vehicle 20 within which is a generator 21 which operates a power supply 22 which in turn energises both the RF quadrupole ion source 2 and electron accelerator 4 of an X-ray generator 23 similar in principle to that described with reference to Figure 1. The X-ray generator 23 is surrounded by further biological shielding 24.

A scraper 25, adapted to remove contaminated soil from its sub-soil, mounted on a framework, which is not shown, is positioned so as to precede the vehicle 20 and a disposal plant 26, which in this case merely deposits decontaminated soil back on the sub-soil is mounted in the same manner as the scraper 25 so as to follow the vehicle 20. The scraper 25 and disposal plant 26 are linked by a continuous conveyor belt 27. The conveyor belt 27 conveys material to be decontaminated from the scraper 25 through a treatment station 28 at which it is exposed to the X-rays from the X-ray generator 23. Extra X-ray shielding 29 is provided underneath the conveyor belt 27 at the treatment station 28 to absorb X-rays which pass through the soil being treated and the conveyor belt 27. The equipment within the vehicle 20 is operated by means of an external control panel 30.

Figure 3 shows in schematic plan a dual beam X-ray source for use in the plant of Figure 2. Each X-ray source is identical to the other and to that of Figure 1.

Hence the same reference numerals are used to denote the same components as in the single beam X-ray source described with reference to Figure 1.

The invention has been described in the form of an embodiment adapted to form a mobile plant to decontaminate soil, but it readily can be adapted for other purposes such as the purification of water by causing the water to flow in a thin sheet through the Xray beam or the decontamination of muds, sludges etc.

The use of DC electron beams to generate the X-ray means that high integrated fluxes of 200- 1 MeV photons are produced. As a result, a high throughput of material and depth of treatment of material can be achieved.

Claims

1. A continuously operating X-ray source comprising, an evacuated chamber including a volume ion source adapted to produce a beam of electrons, an accelerator adapted to accelerate the electrons to a desired energy, a defocusing magnet, a target adapted to produce X-rays of a pre-determined maximum energy as a result of bombardment by the beam of electrons, and means for preventing X-rays from impinging on the electron accelerator.

2. An X-ray source.according to Claim 1 wherein the target is incorporated in a vacuum window.

3. An X-ray source according to Claim 2 wherein the Xray target comprises a layer of a metal adapted to produce the X-rays deposited upon an aluminium window.

4. An X-ray source according to any of Claims 1 to 3 wherein the means for preventing X-rays from impinging on the electron accelerator comprises a beam-deflecting magnet situated between the electron accelerator and the X-ray target.

5. A method of processing a material comprising the operation of subjecting a layer of the material to irradiation by X-rays having an energy of less than 1 MeV.

6. An apparatus for processing a material including an X-ray source according to any of Claims 1 to 4 for generating X-rays having an energy less than 1 MeV and means for passing a material to be processed through the beam of X-rays in the form of a thin layer such that the X-rays can penetrate the layer of material.

7. An apparatus according to Claim 6 comprising a vehicle which can be moved over a region of a contaminated surface, the vehicle including a power supply, an X-ray source according to any of Claims 1 to 5, means for removing contaminated material from the surface, means for transporting the contaminated material to a treatment station where it is exposed to the beam of X-rays and means for delivering decontaminated material to a disposal point.

8. An apparatus according to Claim 7 wherein the means for removing contaminated material from the surface comprises a scraper.

9. An apparatus according to Claim 7 or Claim 8 wherein the means for transporting the contaminated material to the treatment station comprises a conveyor belt.

10. An X-ray source substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

11. An apparatus for the processing of materials substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.