Target for production of x-rays

• US 6,463,123 B1
• Filed: 11/09/2000
• Issued: 10/08/2002
• Est. Priority Date: 11/09/2000
• Status: Expired due to Fees

• Current Assignee: Steris Corporation
• Original Assignee: Steris Corporation
• Inventors: Korenev, Sergey Alexandrovich
• Primary Examiner(s): Kim, Robert H.
• Assistant Examiner(s): Ho, Allen C.
• Application Number:
  US09/710,745
• Time in Patent Office: 698 Days
• Field of Search: 378/64, 378/69, 378/68, 378/119, 378/121, 378/124, 378/143
• US Class Current: 378/69
• CPC Class Codes: G21K 5/10 with provision for relative movement of beam source and object to be irradiated
• CPC Class Codes: H01J 2235/088 Laminated targets, e.g. plurality of emitting layers of unique or differing materials
• CPC Class Codes: H01J 2235/1204 of the anode
• CPC Class Codes: H01J 2235/1262 Circulating fluids
• CPC Class Codes: H01J 35/13 Active cooling, e.g. fluid flow, heat pipes
• CPC Class Codes: H05H 6/00 Targets for producing nuclear reactions supports for targets or objects to be irradiated G21K5/08 ; preparation of tritium C01B4/00; targets, e.g. pellets for fusion reactions by laser or charged particles beam injection H05H1/22

Abstract

A source of electrons (10) generates a beam of free electrons which are accelerated through a vacuum chamber and collide with a target (34). The target has multiple layers of a high Z material such as tungsten or tantalum or for producing x-ray radiation when bombarded with high energy electrons. The target layers are located in sequence such that electrons that are not terminated in the first layer will pass to the second layer, and so on. This provides more efficient use of the generated electrons. The target layers are sandwiched between layers of a thermally conductive, low Z metal substrate (40), such as aluminum or copper or other material with a high thermal conductivity. Hollow passages (42) are bored in the substrate (40) to allow water or some other coolant to flow within them. As electrons strike the target (34), unwanted heat is generated along with the x-rays. The water carries the heat away from the target. As the passages are within the substrate, the water never comes into contact with the target material, and therefore, the life of the target is extended because oxidation and corrosion due to water exposure is inhibited.

Claims

1. A product irradiation device comprising:

an electron accelerator that supplies accelerated electrons;

a multi-layered target upon which the accelerated electrons generated by the accelerator impinge and lose kinetic energy, some of the kinetic energy being converted into x-rays;

a radiation shield that protects areas surrounding an x-ray treatment region from stray radiation;

a product conveyer upon which a product is propagated through the treatment region at a selected speed;

an operator accessible control system that coordinates the operation of the electron accelerator, the product conveyer, and the coolant system.

2. The product irradiation device as set forth in claim 1, wherein the x-ray source further includes a thermally conductive substrate divided into multiple layers and interleaved between the multi-layered target.

3. The product irradiation device as set forth in claim 2, wherein the target layers are coatings of target material upon the substrate.

4. The product irradiation device as set forth in claim 1, wherein the target includes layers of tantalum or tungsten foil.

5. The product irradiation device as set forth in claim 1, wherein the source of x-rays further includes:

an evacuated chamber through which the electrons travel after leaving the source of electrons, before impinging upon the target.

6. The product irradiation device as set forth in claim 5, wherein the source of x-rays further includes:

deflective elements on the periphery of the evacuated chamber for manipulating a direction of propagation of the electrons, thereby temporally varying a spot upon the target upon which the electrons are incident.

7. The product irradiation device as set forth in claim 1, wherein the multi-layered target comprises:

a first target layer which produce s a first x-ray spectrum as a result of interactions with electrons from the electron source;

a second target layer which produces a second x-ray spectrum as a result of interactions with electrons from the electron source; and

,

a third target layer which produces a third x-ray spectrum as a result of interactions with electrons from the electron source.

8. The product irradiation device as set forth in claim 1, further including:

an optical sensing device that senses when a product is and is not in the sterilization region and directs the electron accelerator to only emit electrons when there is product in the sterilization region.

9. A product irradiation device comprising:

a source of radiation that emits x-rays into a treatment region, the source of radiation including;

a plurality of target layers which convert accelerated electrons into x-rays;

a plurality of thermally conductive layers interleaved between the target layers, cavities being defined through the conductive layers through which the coolant fluid flows to draw heat away from the target layers;

an electron accelerator that supplies the accelerated electrons and electron acceleration potentials to the source of x-rays;

a coolant system which pumps a coolant fluid from a remote location through the conductive layer cavities to cool the source of radiation;

a radiation shield that protects surrounding areas from stray radiation;

a product conveyer upon which a product is propagated through the treatment region at a selected speed;

an operator control that coordinates the operation of the electron accelerator and the product conveyer.

10. The product irradiation device as set forth in claim 9, wherein the coolant fluid is water.

11. A product irradiation system comprising:

a conveyor which conveys products past a scan horn;

an electron accelerator which accelerates electrons to at least 1 MeV;

an evacuated path which conveys the accelerated electrons to the scan horn;

an electron sweeping system which sweeps the accelerated electrons across the scan horn;

a face plate on the scan horn of thermally conductive, lower Z material, coolant fluid channels being defined in the face plate; and

,

an anode target of a higher Z material than the face plate mounted to the face plate to convert the accelerated electrons into x-rays for irradiation of the products and into heat, coolant in the face plate coolant channels removing the heat.

12. The product irradiation system as set forth in claim 11, wherein the electron sweeping system sweeps the electrons transversely and longitudinally across the target.

13. A product irradiation system comprising:

an electron accelerator which accelerates electrons to at least 1 MeV;

a target on the scan horn including a plurality of layers of high Z metal interleaved with layers of thermally conductive low Z metal, the high Z metal converting the accelerated electrons into x-rays and heat and the thermally conductive low Z metal conducting the heat from the high Z metal;

an electron sweeping system which sweeps the accelerated electrons across the target;

a conveyor which conveys products through the x-rays.

14. A method of x-ray production comprising:

generating and accelerating an electron beam;

striking a first layer of a target with the electron beam converting a first portion of the electrons into x-rays of a first energy spectrum, a second portion of the electrons passing through the first target layer;

striking with the second portion of electrons a second layer of target, converting a third portion of the electrons into x-rays of a second energy spectrum, a fourth portion of the electrons passing through the second target layer; and

,

conducting heat through thermally conductive layers sandwiched between the target layers.

15. The method as set forth in claim 14, further including:

striking at least one additional target layer with electrons that passed through the second target layer producing x-rays of a third energy spectrum.

16. A method of x-ray production comprising:

generating and accelerating an electron beam;

striking a first layer of a target with the electron beam converting a first portion of the electrons into x-rays of a first energy spectrum, a second portion of the electrons passing through the first target layer;

striking with the second portion of electrons a second layer of target, converting at least part of the second portion of the electrons into x-rays of a second energy spectrum; and

,

dissipating heat generated in the target by;

conducting heat through thermally conductive layers sandwiched between the target layers;

running a cooling fluid through thermally conductive material connected to the thermally conductive layers.

17. An x-ray target for closing an evacuated chamber through which high energy electrons travel, the target comprising:

multiple layers of high Z target material; and

,

multiple layers of thermally conductive low Z substrate interleaved between the target layers.

18. The x-ray target as set forth in claim 17, further including cavities remote from the target layers through which a coolant fluid flows to draw heat from the low Z substrate layers, without physically contacting the target.

19. The x-ray target as set forth in claim 17 further including:

deflecting plates located adjacent the periphery of the evacuated chamber for manipulating the path of the electron beam in two dimensions.