Radiation detector with an ionizable gas atop an integrated circuit

• US 4,970,391 A
• Filed: 02/13/1989
• Issued: 11/13/1990
• Est. Priority Date: 01/27/1987
• Status: Expired due to Term

• Current Assignee: Ongard Systems, Inc.
• Original Assignee: Medrad Incorporated (Bayer AG)
• Inventors: Uber, Arthur E. III
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US07/310,198
• Time in Patent Office: 638 Days
• Field of Search: 250/386, 250/387, 250/388, 250/389, 250/374, 250/385.1
• US Class Current: 250/374
• CPC Class Codes: G01T 1/185 with ionisation chamber arrangements
• CPC Class Codes: G01T 7/125 Alarm- or controlling circuits using ionisation chambers, proportional counters or Geiger-Mueller tubes, also functioning as UV detectors measuring radiation intensity with counting tubes G01T1/18; measuring radiation intensity with ionisation chambers G01T1/185; flame monitoring in combustion devices F23Q7/00, F23N; fire alarms actuated by presence of radiation of particles, e.g. of infrared radiation, of ions G08B17/11; discharge tubes per se H01J47/00
• CPC Class Codes: H01J 47/02 Ionisation chambers

Abstract

The radiation detector includes tissue equivalent bubbles of plastic defining volumes of gas to be ionized by radiation. One or more integrated circuit (ICs) are disposed below the volumes of gas and a collecting electrode on the IC is in direct contact with the gas. Circuitry for generating an electric field within the volume of gas moves the ions therein to the collecting electrode. The collecting electrode is part of an amplifying circuit disposed within the IC. The output from the amplifier is representative of the collected ions and therefore representative of the radiation. The signal from the amplifier is sent to an interface which conditions, buffers and stores the signal. The radiation dose and dose rate are computed in the interface. A communications section transfers that data from the radiation detector. A separate calibration and display unit calibrates the interface by controlling the conditioning of the signal. An area monitor and air monitor are further enhancements of the radiation detector. The radiation detector includes several circuitry arrangements for minimizing inaccuracies due to leakage currents to the collecting electrode from the amplifying circuit. Such circuitry arrangements include duplicate discharge and amplifying circuits not connected to a functioning collecting electrode; subtracting circuitry for subtracting a signal valued proportional to the leakage current; and a current source inducing current opposite in polarity to the leakage current.

Claims

1. A radiation detection system for measuring radiation, the system comprising:

a radiation detector having at least one radiation detection subassembly including;

means for defining a volume of gas, said gas being a detection medium adapted to be ionized by said radiation;

a surface element positioned in direct contact with said gas and being part of said means for defining a volume of gas;

means for generating an electric field within said volume of gas and for collecting ions present therein including at least one collecting electrode positioned on said surface element for collecting ions created in said ionizable gas;

amplifying means electrically connected to said collecting electrode for generating a signal representative of the collected ions;

controlled discharge means for removing charge from said collecting electrode; and

means for minimizing inaccuracies in said system due to leakage currents to said collecting electrode from said discharge means or said amplifying means;

interface means for buffering said signal generated by said amplifying means;

detector control means for controlling said controlled discharge means; and

means for supplying power to said at least one radiation detection subassembly and said detector control means.

2. The system of claim 1, wherein an input to said amplifying means at said collecting electrode is sealed within the volume of gas and isolated from moisture, and wherein said collecting electrode is electrically isolated from elements outside of said volume of gas.

3. The system of claim 1, wherein said controlled discharge means comprises a transistor that unintentionally introduces a leakage current into the collecting electrode, said leakage current being controlled by said means for minimizing inaccuracies.

4. The system of claim 3, wherein said means for minimizing inaccuracies comprises a current source for inducing current of a polarity opposite to that of the leakage current flowing to the collecting electrode, said current source being controlled by said detector control means.

5. The system of claim 4, and further comprising a duplicate controlled discharge means and a duplicate amplifying means, said duplicate amplifying means and said duplicate controlled discharge means being not connected to said collecting electrode, and supplying electrical signal information to said detector control means for controlling said current source.

6. The system of claim 1, and further comprising a duplicate controlled discharge means and a duplicate amplifying means, said duplicate amplifying means and said duplicate controlled discharge means being not connected to said collecting electrode, and producing an output signal fed to said detector control means for minimizing inaccuracies due to leakage current.

7. The system of claim 1, wherein said controlled discharge means removes charge from said collecting electrode in predetermined size packets of charge, said controlled discharge mans producing as output a pulse for each packet of charge removed from said collecting electrode so that the number of pulses produced as output by said controlled discharge means is a measure of the charge collected on said collecting electrode, and the rate of said pulses is related to the current to the collecting electrode.

8. The system of claim 7, and further comprising a voltage source, and wherein said controlled discharge means comprises two transistors connected in series between said collecting electrode and said voltage source, said transistors being controlled and switched sequentially so that only one transistor conducts at any one instant in time for removing predetermined size packets of charge from the collecting electrode and delivering said charge to said voltage source.

9. The system of claim 7, and further comprising counting means forming a part of said detector control means for counting events corresponding to the removal of charge by said controlled discharge means, and wherein said means for minimizing inaccuracies comprises means for controlling said counting means to ignore charge removal events if said charge removal events do not occur more frequently than a predetermined frequency.

10. The system of claim 1, wherein said means for minimizing inaccuracies comprises means for not permanently electrically connecting said controlled discharge means to said collecting electrode under control of said detector control means.

11. The system of claim 10, wherein said controlled discharge means uses induced conductivity in the detection medium for controlled discharge.

12. The system of claim 10, wherein said controlled discharge means uses induced conductivity in the detection medium for controlled discharge, said conductivity being induced by the radiation being measured.

13. The system of claim 12, wherein said detector control means includes means for sensing successive accumulations of charge on the collecting electrode and said controlled discharge means is connected to the means for supplying power for reversing the polarity of said electric field within said volume of gas for attracting charges of one polarity to said collecting electrode, and then attracting charges of a polarity, opposite to said first polarity, to said collecting electrode.

14. The system of claim 13, wherein said detector control means controls said controlled discharge means so that measurements can be made while said electric field is of either polarity.

15. The system of claim 1, and further comprising means within the detector control means for enabling measurement of radiation over a total dose rate range that extends beyond the range of any single unmodified radiation detection subassembly.

16. The system of claim 15, wherein said detector control means includes selecting means to select a particular radiation detection subassembly for measuring radiation within its predetermined accurate dose rate range.

17. The system of claim 15, wherein said detector control means selects a signal representative of the collected charge on one of several collecting electrodes from within a radiation detection subassembly.

18. The system of claim 1, wherein said radiation detection subassembly is capable of sensing charge or current, and further includes means for generating a numeric representation of the collected charge or current, accumulating means for accumulating a numeric representation of the sensed charge or current, and communicating means for communicating said numeric representation upon command of said detector control means, or in accordance with programmed instructions.

19. The system of claim 18, and further including means for storing numeric information used in the operation and accumulation of said numeric representation of said sensed charge or current.

20. The system of claim 19, and further comprising error detection and correction means for minimizing errors in communication of said numeric representation of said sensed charge or current.

21. The system of claim 11, and further comprising an integrated circuit;

wherein said amplifying means includes at least one input transistor mounted on said integrated circuit; and

wherein said integrated circuit is located in close proximity to said collecting electrode.

22. The system of claim 21, wherein an input to said amplifying means at said collecting electrode is sealed within the volume of gas and isolated from moisture, and wherein said collecting electrode is electrically isolated from elements outside of said volume of gas.

23. The system of claim 22, wherein said controlled discharge means comprises a transistor that unintentionally introduces a leakage current into the collecting electrode, said leakage current being controlled by said means for minimizing inaccuracies.

24. The system of claim 23, wherein said means for minimizing inaccuracies comprises a current source for inducing current of a polarity opposite to that of the leakage current flowing to the collecting electrode, said current source being controlled by said detector control means.

25. The system of claim 24, an d further comprising a duplicate controlled discharge means and a duplicate amplifying means, said duplicate amplifying means and said duplicate controlled discharge means being not connected to said collecting electrode, and supplying electrical signal information to said detector control mans for controlling said current source.

26. The system of claim 21, and further comprising a duplicate controlled discharge means and a duplicate amplifying means, said duplicate amplifying means and said duplicate controlled discharge means being not connected to said collecting electrode, and producing an output signal fed to said detector control means for minimizing inaccuracies due to leakage current.

27. The system of claim 21, wherein said controlled discharge means removes charge from said collecting electrode in predetermined size packets of charge, said controlled discharge means producing as output a pulse for each packet of charge removed from said collecting electrode so that the number of pulses produced as output by said controlled discharge mans is a measure of the charge collected on said collecting electrode, and the rate of said pulses is related to the current to the collecting electrode.

28. The system of claim 27, and further comprising a voltage source, and wherein said controlled discharge means comprises two transistors connected in series between said collecting electrode and said voltage source, said transistors being controlled and switched sequentially so that only one transistor conducts at any one instant in time for removing predetermined size packets of charge from the collecting electrode and delivering said charge to said voltage source.

29. The system of claim 27, and further comprising counting means forming a part of said detector control means for counting events corresponding to the removal of charge by said controlled discharge means, and wherein said means for minimizing inaccuracies comprises means for controlling said counting means to ignore charge removal events if said charge removal events do not occur more frequently than a predetermined frequency.

30. The system of claim 21, wherein said means for minimizing inaccuracies comprises means for not permanently electrically connecting said controlled discharge means to said collecting electrode under control of said detector control means.

31. The system of claim 30, wherein said controlled discharge means uses induced conductivity in the detection medium for controlled discharge.

32. The system of claim 30, wherein said controlled discharge means uses induced conductivity in the detection medium for controlled discharge, said conductivity being induced by the radiation being measured.

33. The system of claim 32, wherein said detector control means includes means for sensing successive accumulations of charge on the collecting electrode and said controlled discharge means is connected to the means for supplying power for reversing the polarity of said electric field within said volume of gas for attracting charges of one polarity to said collecting electrode, and then attracting charges of a polarity, opposite to said first polarity, to said collecting electrode.

34. The system of claim 33, wherein said detector control means controls said controlled discharge means so that measurements can be made while said electric field is of either polarity.

35. The system of claim 21, and further comprising means within the detector control means for enabling measurement of radiation over a total dose rate range that extends beyond the range of any single unmodified radiation detection subassembly.

36. The system of claim 35, wherein said detector control means includes selecting means to select a particular radiation detection subassembly for measuring radiation within its predetermined accurate dose rate range.

37. The system of claim 35, wherein said detector control means selects a signal representative of the collected charge on one of several collecting electrodes from within a radiation detection subassembly.

38. The system of claim 21, and further comprising a guard ring mounted on the surface of said integrated circuit, said guard ring being kept at the same potential as said collecting electrode to intercept leakage current to said collecting electrode.

39. The system of claim 38, wherein said guard ring is sized to minimize induction of voltage onto said collecting electrode due to the presence of nearby conductive material on said integrated circuit.

40. The system of claim 38, and further comprising a capacitor formed on the integrated circuit connected to the gate of said input transistor for controllably changing the voltage of the gate without inducing a leakage current.

41. The system of claim 21, wherein said radiation detection subassembly is capable of sensing charge or current, and further includes means for generating a numeric representation of the collected charge or current, accumulating means for accumulating a numeric representation of the sensed charge or current, and communicating means for communicating said numeric representation upon command of said detector control means, or in accordance with programmed instructions.

42. The system of claim 41, and further including means for storing numeric information used in the operation and accumulation of said numeric representation of said sensed charge or current.

43. The system of claim 42, and further comprising error detection and correction means for minimizing errors in communication of said numeric representation of said sensed charge or current.

44. The system of claim 1, and further comprising an unpackaged integrated circuit;

wherein said surface element in mounted on said unpackaged integrated circuit; and

wherein said amplifying means includes an input transistor mounted on said integrated circuit.

45. The system of claim 44, wherein an input to said amplifying means at said collecting electrode is sealed within the volume of gas and isolated from moisture, and said collecting electrode is electrically isolated from elements outside of said volume of gas.

46. The system of claim 44, wherein said controlled discharge means comprises a transistor that unintentionally introduces a leakage current into the collecting electrode, said leakage current being controlled by said means for minimizing inaccuracies.

47. The system of claim 46, wherein said means for minimizing inaccuracies comprises a current source for inducing current of opposite polarity than the leakage current to flow to the collecting electrode, said current source being controlled by the detector control means.

48. The system of claim 47, and further comprising a duplicate controlled discharge means and a duplicate amplifying means, said duplicate amplifying means and said duplicate controlled discharge means not being connected to said collecting electrode, said duplicate controlled discharge means and duplicate amplifying means supplying electrical signal information to said detector control mans for controlling said current source.

49. The system of claim 44, and further comprising a duplicate controlled discharge means and a duplicate amplifying means, said duplicate amplifying means and said duplicate controlled discharge being not connected to said collecting electrode, and producing an output signal fed to said detector controller means for minimizing inaccuracies due to the leakage current.

50. The system of claim 44, wherein said controlled discharge means removes charge from said collecting electrode in predetermined size packets of charge, said controlled discharge means producing as output a pulse for each packet of charge removed from said collecting electrode so that the number of pulses produced as output by said controlled discharge means is a measure of the charge collected on said collecting electrode, and the rate of said pulses is related to the current to the collecting electrode.

51. The system of claim 50, and further comprising a voltage source;

and wherein said controlled discharge means comprises two transistors connected in series between said collecting electrode and said voltage source, said transistors being controlled and switched sequentially so that only one transistor conducts at any one instant in time for removing predetermined size packets of charge from the collecting electrode and delivering said charge to said voltage source.

52. The system of claim 50, and further comprising counting means forming a part of said detector control means for counting events corresponding to the removal of charge by said controlled discharge means, and wherein said means for minimizing inaccuracies comprises means for controlling said counting means to ignore charge removal events if said charge removal events do not occur greater than a predetermined frequency.

53. The system of claim 44, wherein said means for minimizing inaccuracies comprises means for not permanently electrically connecting said controlled discharge means to said collecting electrode under control of said detector control means.

54. The system of claim 53, wherein said controlled discharge means uses induced conductivity in the detection medium for controlled discharge.

55. The system of claim 53, wherein said controlled discharge means uses induced conductivity in the detection medium for controlled discharge, said conductivity being induced by the radiation being measured.

56. The system of claim 55, wherein said detector control means includes means for sensing successive accumulations of charge on the collecting electrode and said controlled discharge means is connected to the means for supplying power for reversing the polarity of said electric field within said volume of gas for attracting charges of one polarity to said collecting electrode, and then attracting charges of a polarity, opposite to said first polarity, to said collecting electrode.

57. The system of claim 56, wherein said detector control mans controls said controlled discharge means so that measurements can be made while said electric field is of either polarity.

58. The system of claim 44, and further comprising means within the detector control means for enabling measurement of radiation over a total dose rate range that extends beyond the range of any single unmodified radiation detection subassembly.

59. The system of claim 58, wherein said detector control means includes selecting means to select a particular radiation detection subassembly for measuring radiation within its predetermined accurate dose rate range.

60. The system of claim 58, wherein said detector control means selects a signal representative of the collected charge on one of several collecting electrode from within a radiation detection subassembly.

61. The system of claim 44, and further comprising a guard ring mounted on the surface of said integrated circuit, said guard ring being kept at the same potential as said collecting electrode to intercept leakage current to said collecting electrode.

62. The system of claim 61, wherein said guard ring is sized to minimize induction of voltage onto said collecting electrode due to the presence of nearby conductive material on said integrated circuit.

63. The system of claim 61, and further comprising a capacitor formed on the integrated circuit connected to the gate of said input transistor for controllably changing the voltage of the gate without inducing a leakage current.

64. The system of claim 44, wherein said radiation detection subassembly is capable of sensing charge or current, and further includes means for generating a numeric representation of the collected charge or current, accumulating means for accumulating a numeric representation of the sensed charge or current, and communicating means for communicating said numeric representation upon command of said detector control means, or in accordance with programmed instructions.

65. The system of claim 64, and further including means for storing numeric information used in the operation and accumulation of said numeric representation of said sensed charge or current.

66. The system of claim 65, and further comprising error detection and correction means for minimizing errors in communication of said numeric representation of said sensed charge or current.