On-line measurement of absorbed electron beam dosage in irradiated product

• US 6,617,596 B1
• Filed: 11/17/2000
• Issued: 09/09/2003
• Est. Priority Date: 11/17/2000
• Status: Active Grant

• Current Assignee: Steris Corporation
• Original Assignee: Steris Corporation
• Inventors: Korenev, Sergey Alexandrovich
• Primary Examiner(s): Berman, Jack
• Assistant Examiner(s): FERNANDEZ, KALIMAH
• Application Number:
  US09/715,481
• Time in Patent Office: 1,026 Days
• Field of Search: 250/208.1, 250/363.1, 250/336.2, 250/397, 250/492.3, 324/370.01, 324/71.3, 324/71.4
• US Class Current: 250/492.3
• CPC Class Codes: G21K 5/00 Irradiation devices discharge tubes for irradiating H01J37/00

Abstract

An accelerator (10) generates an electron beam (22) of selected energy that is swept (16) up and down. A conveyor (32) moves items (30) through the electron beam for irradiation treatment. An array (40a) of inductive electron beam strength detectors is disposed on a down stream side of the item to detect the energy of the electron beam exiting the item at the plurality of altitudes. The electron beam strength entering and leaving the item are communicated to a processor (54) which determines the absorbed dose of radiation absorbed by the item. The dose information is archived (56) or compared by a parameter adjustment processor (58) with target doses and deviations are used to control one or more of MeV or beam current of the electron beam, the sweep rate, and the conveying speed of the items. Each of the detectors includes a vacuum chamber in which two current transformers (60, 62) disposed on either side of a metal foil layer (64). From the difference in the current induced in the two transformers by a pulsed, collimated electron beam, the energy of the beam is determined.

Claims

1. A method of irradiating comprising:

moving items through a charged particle beam;

determining a kinetic energy of the charged particle beam entering the item; and

,

measuring a kinetic energy of the charged particle beam exiting the item.

2. The method as set forth in claim 1, further including:

determining a difference between the energy of the charged particle beam entering and exiting the item; and

,

determining an absorbed dosage of the charged particle beam from the difference.

3. The method as set forth in claim 2, further including:

controlling at least one of a speed with which the items move through the charged particle beam and the energy of the charged particle beam in accordance with the determined absorbed dose.

4. The method as set forth in claim 1, wherein:

the items are conveyed through the charged particle beam in a first direction; and

,

the charged particle beam is swept back and forth in a plane perpendicular to the first direction.

5. The method as set forth in claim 1, wherein the charged particle beam is an electron beam.

6. The method as set forth in claim 1, further including:

determining a beam current absorbed by the irradiated product.

7. The method as set forth in claim 1, further including:

scanning the charged particle beam; and

,

measuring beam current pulses as the beam current scans past a measurement point.

8. A method of irradiating comprising:

irradiating items with a charged particle beam;

determining an energy of the charged particle beam entering the item including measuring changes in a charged particle beam current; and

determining an energy of the charged particle beam exiting the item including measuring changes in a charged particle beam current.

9. The method as set forth in claim 8, further including:

measuring the charged particle beam current at a plurality of locations along the item.

10. The method as set forth in claim 9, further including:

determining reductions in the charged particle beam current at the various points along the item and determining an absorbed dose for a plurality of regions of the item from the reduced current.

11. The method as set forth in claim 8, wherein the measuring of the charged particle beam current includes:

concentrating magnetic flux changes attributable to the changing current; and

with concentrated magnetic flux changes, inducing electrical currents in windings of a coil.

12. A method of detecting energy of an electron beam, the method comprising:

collimating an electron beam to a preselected cross-section;

inducing a first electromotive force with the collimated electron beam;

attenuating the collimated electron beam;

inducing a second electromotive force with the attenuated electron beam; and

,

comparing the first and second electromotive forces.

13. The method as set forth in claim 12, wherein:

inducing the first electromotive force includes pulsing the collimated electron beam through a first annular winding;

attenuating the collimated electron beam includes passing the electron beam through a metal layer of preselected thickness; and

,

inducing the second electromotive force includes pulsing the collimated electron beam through a second annular winding, the second annular winding being disposed closely adjacent the metal layer.

14. An irradiation apparatus comprising:

a charged particle beam generator for generating and aiming a charged particle beam of a first kinetic energy along a preselected path;

a conveyor which conveys items to be irradiated through the beam; and

,

a beam kinetic energy monitor for monitoring a second kinetic energy of the beam after it has passed through the item.

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

a processor for comparing the first and second beam energies and determining a dose of the charged particle beam absorbed by the item.

16. The apparatus as set forth in claim 15, wherein the processor is disposed remote from the monitors and further including:

a transducer for converting an output of the monitors into optical signals, the transducer being disposed adjacent the monitor such that the output from the monitor is conveyed from the irradiation region in an optical format.

17. The apparatus as set forth in claim 15, wherein the beam generator includes a beam strength control circuit for controlling at least one of charged particle beam voltage and current and wherein the conveyor includes a speed control circuit for controlling a speed with which the items are moved through the charged particle beam, and further including:

a parameter adjustment processor which compares the determined absorbed doses with target absorbed doses and selectively adjusts at least one of the beam strength control circuit and the conveyor speed control circuit.

18. The apparatus as set forth in claim 17, wherein the charged particle beam generator further includes a sweep control circuit for sweeping the charged particle beam back and forth across at least one of a planar region and a volumetric region and wherein the beam strength monitor includes:

first and second current transformers in which a current is induced by the electron beam;

a metal absorbing foil disposed between the first and second current transformers whereby the current induced the second current transformer is less than the current induced the first current transformer; and

,

a vacuum chamber in which the first and second current transformers and the absorbing foil are disposed.

19. The apparatus as set forth in claim 14, wherein the charged particle beam generator includes an electron accelerator.

20. An energy detector comprising:

first and second inductive coils in which currents are induced by an electron beam;

a metal layer of preselected thickness disposed between the first and second inductive coils;

a beam collimator upstream of the inductive coils which collimates the electron beam to a preselected cross-section.

21. The energy detector as set forth in claim 20, further including:

a vacuum chamber in which the inductive coils and the metal foil are disposed.

22. A method of irradiating comprising:

moving items through a charged particle beam;

determining a kinetic energy of the charged particle beam entering the item;

measuring a kinetic energy of the charged particle beam exiting the item;

determining an absorbed kinetic energy by subtracting the kinetic energy of the charged particle beam exciting the item from the kinetic energy of the beam before entering the item;

dividing the determined absorbed kinetic energy by a mass of the item irradiated by the charged particle beam.

23. The method as set forth in claim 22, further including:

determining a charge deposited in the irradiated item by the absorbed charged particle beam.

24. The method as set forth in claim 23, further including:

multiplying the absorbed kinetic energy by the deposited charge.

25. The method as set forth in claim 24, wherein determining the deposited charge includes:

measuring a beam current of the charged particle beam after irradiating the product.

26. An irradiating method including:

collimating a charged particle beam to a preselected cross-section;

passing the charged particle beam through an item;

determining the energy of the beam entering the item by inducing a first electromotive force with the collimated beam;

attenuating the collimated beam with the item;

determining the energy of the beam exiting the item by inducing a second electromotive force with the attenuated electron beam; and

,

comparing the first and second electromotive forces.

27. A method of determining an absorbed dose deposited by an electron beam in an irradiated product comprising:

determining an absorbed kinetic energy by subtracting a final kinetic energy of the electron beam exciting the product from an initial kinetic energy of the beam before entering the product;

dividing the determined absorbed kinetic energy by a mass of the product irradiated by the electron beam.

28. An irradiation apparatus comprising:

a charged particle beam generator for generating and aiming a charged particle beam of a first energy along a preselected path;

a conveyor which conveys items to be irradiated through the beam; and

,

a beam strength monitor for monitoring a second energy of the beam after it has passed through the item, the monitor including;

a vacuum chamber;

first and second current transformers;

a foil having known absorption characteristics disposed between of the first current transformer and the second current transformer.

29. The apparatus as set forth in claim 28, further including:

a collimator disposed upstream of the current transformers for collimating the charged particle beam before it passes through the first current transformer, foil, and the second current transformer.

30. The apparatus as set forth in claim 28, further including:

a comparitor which compares the currents induced in the first and second current transformers and determines therefrom the energy of the charged particle beam.

31. An apparatus for detecting energy of an electron beam, the apparatus comprising:

a means for collimating an electron beam to a preselected cross-section;

a first means in which the collimated electron beam induces a first electromotive force before being attenuated;

a second means in which the electron beam induces a second electromotive force after the collimated electron beam has been attenuated; and

,

a means for comparing the first and second electromotive forces.

32. An apparatus for determining an absorbed dose deposited by an electron beam in an irradiated product comprising:

a means for subtracting a final kinetic energy of the electron beam exciting the product from an initial kinetic energy of the beam before entering the product;

a means for dividing the difference between the initial and final kinetic energy by a mass of the product irradiated by the electron beam.