Real time monitoring of electron beam radiation dose

• US 6,429,444 B1
• Filed: 08/24/1999
• Issued: 08/06/2002
• Est. Priority Date: 08/24/1999
• Status: Expired due to Fees

• Current Assignee: Steris Corporation
• Original Assignee: Steris Corporation
• Inventors: Korenev, Sergey Alexandrovich, Johnson, Stephen Scott, Masefield, John, Kriebel, Jerry
• Primary Examiner(s): BERMAN, JACK I
• Application Number:
  US09/382,051
• Time in Patent Office: 1,078 Days
• Field of Search: 250/492.3, 250/397, 324/71.3
• US Class Current: 250/492.3
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
• CPC Class Codes: G21K 5/04 with beam-forming means
• CPC Class Codes: G21K 5/10 with provision for relative movement of beam source and object to be irradiated

Abstract

An accelerator (10) generates an electron beam that is swept (16) up and down to form an electron beam (22). A conveyor (32) moves items (30) through the electron beam for irradiation treatment. A first array of inductive electron beam strength detectors'"'"' (40a) is disposed between the origin of the electron beam and a first item to be irradiated to measure the strength of the electron beam entering the item at a plurality of altitudes. A second array (42) of inductive electron beam strength detectors is disposed on the opposite side of the item to detect the strength of the electron beam exiting the item at the plurality of altitudes. In the illustrated embodiment, another item is positioned to be irradiated by the radiation that is passed through the first item. The second array thus detects the electron beam strength entering the second item and an analogous array (40c) measures the electron beam strength exiting the second item. A processor (54) determines the absorbed dose of radiation absorbed by each of the first and second items. The dose information is archived (56). The dose information is 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 inductive detectors (42) includes a ferrite member, such as a ferrite ring (62). A plurality of coiled loops (64) are mounted around a periphery of the ferrite ring.

Claims

1. A method of irradiating comprising:

moving items through a charged particle beam;

measuring energy of the charged particle beam entering the item; and

,

measuring 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.

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 4 wherein the detecting of the charged particle beam includes inductively measuring changes in a charged particle beam current.

6. The method as set forth in claim 5 further including inductively measuring charged particle beam current at a plurality of locations along the item.

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

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

8. The method as set forth in claim 5 wherein the inductive detection of the charged particle beam current includes:

concentrating magnetic flux changes attributable to the changing current with a ferrite member; and

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

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

10. An irradiation apparatus comprising:

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

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

a first beam strength monitor disposed between the item and the beam generator for measuring a strength of the beam before entering the item; and

,

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

11. The apparatus as set forth in claim 10 further including:

a processor for comparing the beam strengths measured by the first and second beam strength monitors and determining a dose of the charged particle beam absorbed by the item.

12. The apparatus as set forth in claim 11 wherein the processor is disposed remote from the monitors and further including:

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

13. The apparatus as set forth in claim 11 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.

14. The apparatus as set forth in claim 11 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 monitors each include:

an array of inductive couplers disposed adjacent the charged particle beam.

15. The apparatus as set forth in claim 14 wherein the array is disposed parallel to the charged particle beam.

16. The apparatus as set forth in claim 14 wherein each of the inductive sensors includes:

a ferrite core;

a plurality of coil windings disposed on the ferrite core.

17. The apparatus as set forth in claim 16 wherein the ferrite core includes a ferrite ring which is mounted parallel to the charged particle beam and wherein the coiled windings lie on a peripheral surface of the ferrite ring.

18. The apparatus as set forth in claim 16 wherein each individual sensor includes:

a ferrite pole which is disposed parallel to the charged particle beam;

a ferrite extension extending from the ferrite pole; and

,

a plurality of windings of a coil extending around the ferrite extension.

19. The apparatus as set forth in claim 10 wherein the charged particle beam generator includes an electron accelerator.

20. A charged particle beam detector comprising:

a ferrite ring which is mounted parallel to the charged particle beam; and

a plurality of coil windings lying on a peripheral surface of the ferrite ring.

21. A charged particle beam detector comprising:

a ferrite pole which is disposed parallel to the charged particle beam;

a ferrite extension extending from the ferrite pole; and

a plurality of coil windings extending around the ferrite extension.

22. An irradiation means comprising:

a means for moving items to be irradiated through a charged particle beam;

a means for measuring energy of the charged particle beam entering the item; and

,

a means for measuring energy of the charged particle beam exiting the item.