Photomultiplier and detection systems

• US 8,389,942 B2
• Filed: 06/11/2009
• Issued: 03/05/2013
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Rapiscan Systems Incorporated (OSI Systems Incorporated)
• Original Assignee: Rapiscan Systems Incorporated (OSI Systems Incorporated)
• Inventors: Morton, Edward James
• Primary Examiner(s): Kim, Kiho
• Application Number:
  US12/997,251
• Publication Number:
  US 20110182407A1
• Time in Patent Office: 1,363 Days
• Field of Search: 25036301-3631, 313/532, 708/839
• US Class Current: 250/363.02
• CPC Class Codes: G01T 1/16 Measuring radiation intensity G01T1/29 takes precedence ; self-powered detectors G01T3/006; using an ionisation chamber filled with a liquid or solid, e.g. frozen liquid, dielectric G01T3/008
• CPC Class Codes: G01T 1/167 Measuring radioactive content of objects, e.g. contamination whole body counters G01T1/163
• CPC Class Codes: G01T 1/208 Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
• CPC Class Codes: G01T 3/06 with scintillation detectors
• CPC Class Codes: G01V 5/222 measuring scattered radiation
• CPC Class Codes: G01V 5/281 detecting special nuclear material [SNM], e.g. Uranium-235, Uranium-233 or Plutonium-239
• CPC Class Codes: H01J 40/04 Electrodes
• CPC Class Codes: H01J 43/08 Cathode arrangements construction of photo cathodes H01J40/06, H01J40/16, H01J47/00, H01J49/08
• CPC Class Codes: H01J 43/18 Electrode arrangements using essentially more than one dynode
• CPC Class Codes: H01J 43/30 Circuit arrangements not adapted to a particular application of the tube and not otherwise provided for

Abstract

The invention provides a switchable photomultiplier switchable between a detecting state and a non-detecting state including a cathode upon which incident radiation is arranged to impinge. The photomultiplier also includes a series of dynodes arranged to amplify a current created at the cathode upon detection of photoradiation. The invention also provides a detection system arranged to detect radiation-emitting material in an object. The system includes a detector switchable between a detecting state in which the detector is arranged to detect radiation and a non-detecting state in which the detector is arranged to not detect radiation. The system further includes a controller arranged to control switching of the detector between the states such that the detector is switched to the non-detecting state while an external radiation source is irradiating the object.

Claims

1. A switchable photomultiplier, wherein said switchable photomultiplier is adapted to be switchable between a detecting state and a non-detecting state, comprising:

a) A cathode, wherein said cathode is arranged to receive incident radiation;

b) A series of dynodes arranged to amplify a current created at the cathode upon detection of said radiation; and

c) A first dynode of the series of dynodes, said first dynode being operatively closest to the cathode and being at a first potential, wherein the electrical potential of the cathode is switchable between a second potential, below a first potential, when the photomultiplier is in the detecting state and a third potential, above the second potential, when the photomultiplier is in the non-detecting state.

2. The photomultiplier of claim 1 wherein the first dynode is electrically grounded.

3. The photomultiplier of claim 1 wherein the third potential is ground.

4. The photomultiplier of claim 1 wherein the third potential is above ground.

5. The photomultiplier of claim 1 wherein the first potential is about 0V, the second potential is about −

165V, and the third potential is about +10V.

6. The photomultiplier of claim 1 wherein the first dynode and cathode are positioned relative to each other such that the capacitive coupling between them is negligible.

7. The photomultiplier of claim 1 wherein a vacuum is provided between the first dynode and the cathode.

8. The photomultiplier of claim 1 wherein the first dynode is held at a low voltage below ground.

9. The photomultiplier of any of claim 8 comprising an anode which is electrically substantially at ground potential.

10. The photomultiplier of claim 1 wherein the third potential is held at a low voltage below ground.

11. A detection system arranged to detect radiation-emitting material in an object, the system comprising:

a) A detector comprising a switchable photomultiplier of claim 1, wherein said detector is switchable between a detecting state in which the detector is arranged to detect radiation and a non-detecting state in which the detector is arranged to not detect radiation; and

b) A controller arranged to control said switching of the detector between the detecting and non-detecting states such that the detector is switched to the non-detecting state while an external radiation source is irradiating the object.

12. The detection system of claim 11 wherein the external radiation source is part of a scanning system arranged to scan the object by irradiating it via the external radiation source and subsequently detecting radiation that passes through the object and/or is scattered by the object.

13. The detection system of claim 11 wherein the detector comprises said photomultiplier coupled with a scintillator.

14. The detection system of claim 11 wherein the external radiation source is arranged to irradiate the object in bursts and the controller is arranged to switch the detector to the non-detecting state during the bursts.

15. The detection system of claim 14 wherein following a burst from the external radiation source, the detector recovers to a condition in which it is able to effectively detect radiation from a radiation-emitting material after a period of time and the controller is arranged to switch the detector to the non-detecting state during the bursts and also during the period of time.

16. The detection system of claim 15 wherein the period of time is less than 10 ms.

17. The detection system of claim 14 wherein the bursts are periodic and occur about every 10 ms and last for about 0.005 ms.

18. The detection system of claim 11 wherein the controller is arranged to switch the detector from the detecting state to the non-detecting state in 10 ns to 1000 ns.

19. The detection system of claim 11 comprising a plurality of detectors arranged such that the position of a radiation-emitting material in the object can be determined.

20. The detection system of claim 11 wherein the controller comprises a push-pull circuit.

21. The detection system of claim 11 wherein the radiation-emitting material comprises a nuclear or radioactive material.

22. The detection system of claim 21 wherein the material comprises uranium, plutonium or a similar material.

23. A detection method for detecting radiation-emitting material in an object comprising:

a) Switching a detector between a detecting state in which the detector is arranged to detect radiation and a non-detecting state in which the detector is arranged to not detect radiation using switchable photomultiplier of claim 1; and

b) Controlling switching of the detector between the states such that the detector is switched to the non-detecting state while an external radiation source is irradiating the object.

24. The method of claim 23 wherein the external radiation source is part of a scanning system arranged to scan the object by irradiating it via the external radiation source and subsequently detecting radiation that passes through the object and/or is scattered by the object.

25. An imaging method, comprising:

a) Creating an image of an object from detected information obtained via the detection method of claim 24; and

b) Determining a position of a radiation-emitting material in the object and overlaying information relating to the detection of radiation-emitting material in the object with information from the scanning system.