Passive solid state microdosimeter with electronic readout

• US 5,596,199 A
• Filed: 02/06/1995
• Issued: 01/21/1997
• Est. Priority Date: 02/06/1995
• Status: Expired due to Term

• Current Assignee: Clemson University
• Original Assignee: Clemson University
• Inventors: Beauvais, W. Joseph, Reed, Robert A., McNulty, Peter J., Roth, David R., Moran, Wanda K.
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US08/383,959
• Time in Patent Office: 715 Days
• Field of Search: 250/370.06, 250/370.07
• US Class Current: 250/370.07
• CPC Class Codes: G01T 1/026 Semiconductor dose-rate meters
• CPC Class Codes: G01T 1/245 using memory cells

Abstract

Apparatus and method for qualitatively and quantitatively analyzing a complex radiation field are provided. A passive microdosimetry detector device records the energy deposition of incident radiation using an array of microstructure non-volatile memory devices. Each microstructure non-volatile memory device is capable of storing a predetermined initial charge without requiring a power source. A radiation particle incident to a microstructure non-volatile memory device is termed an "event". Each such event may generate a charge within a sensitive volume defined by the microstructure non-volatile memory device. The charge generated within the sensitive volume alters the stored initial charge by an amount falling within a range corresponding to the energy deposited by certain particle types. Data corresponding to such charge alterations for a plurality of microstructure non-volatile memory devices within an array of such devices are presented to a qualitative analyzing device. The qualitative analyzing device converts the data to a spectral analysis of the incident radiation field by applying ICRP-recommended weighting factors to individual events or approximations thereof.

Claims

1. A passive microdosimetry detector device for recording the energy deposition of radiation incident thereto and enabling qualitative analysis of a complex radiation field, comprising an array of microstructure non-volatile memory devices, a plurality of said microstructure non-volatile memory devices each defining a corresponding microstructure sensitive volume within which charge is generated responsive to incident radiation and wherein at least one of said non-volatile memory devices is configured to store a predetermined initial charge such that said generated charge measurably alters said predetermined initial charge stored by said at least one microstructure non-volatile memory device.

2. The passive microdosimetry detector as in claim 1, wherein said plurality of memory devices are each configured to store a predetermined initial charge such that a charge generated in its corresponding sensitive volume measurably alters the predetermined initial charge stored thereby.

3. The passive microdosimetry detector as in claim 1, wherein said array of microstructure non-volatile memory devices comprises a semiconductor device.

4. The passive microdosimetry detector as in claim 3, wherein said semiconductor device is configured to individually address said at least one microstructure non-volatile memory device.

5. The passive microdosimetry detector as in claim 4, wherein said semiconductor device comprises an erasable programmable read only memory chip.

6. The passive microdosimetry detector as in claim 3, wherein said semiconductor device is configured to permit the individual measurement of said at least one microstructure non-volatile memory device by a measurement device.

7. The passive microdosimetry detector as in claim 1, further comprising shielding about said at least one microstructure non-volatile memory device so as to simulate specific biological tissue.

8. The passive microdosimetry detector as in claim 1, wherein each of said microstructure sensitive volumes is generally not more than one cubic micrometer.

9. The passive microdosimetry detector as in claim 8, wherein each of said microstructure sensitive volumes is approximately 0.1 micrometers by 1.0 micrometer by 100 angstroms thick with respect to the incidence of said radiation.

10. The passive microdosimetry detector as in claim 8, wherein each of said microstructure sensitive volumes is approximately the size of a biological cell nucleus.

11. The passive microdosimetry detector as in claim 8, wherein each of said microstructure sensitive volumes is approximately the size of a DNA genome.

12. The passive microdosimetry detector as in claim 1, wherein said predetermined initial charge is stored on an electrically insulated gate within each said at least one microstructure non-volatile memory device.

13. The passive microdosimetry detector as in claim 1, wherein said predetermined initial charge on said at least one microstructure non-volatile memory device is set relative to a known threshold charge such that traversal of said known threshold charge from said predetermined initial charge causes said at least one microstructure non-volatile memory device to change state.

14. The passive microdosimetry detector as in claim 13, wherein said at least one microstructure non-volatile memory device is configure such that incident radiation causes a charge alteration from said predetermined initial charge towards said threshold level.

15. A passive microdosimetry system for qualitatively analyzing radiation incident thereon in a complex radiation field, comprising:

at least one detector array of microstructure non-volatile memory devices, a plurality of said devices each defining a corresponding microstructure sensitive volume within which charge is generated responsive to incident radiation and wherein at least one of said microstructure non-volatile memory devices is configured to store a predetermined initial charge such that said generated charge measurably alters said predetermined initial charge stored by said at least one microstructure non-volatile memory device;

a measurement device operatively associated with said detector array, comprising

communicating device for communicating with said at least one detector array,

measuring mechanism for measuring said charge generated on said at least one microstructure non-volatile memory device; and

a qualitative analyzing device operatively associated with said measurement device for converting said generated charge to a qualitative analysis of the complex radiation field.

16. The passive microdosimetry system as in claim 15, wherein said at least one detector array of microstructure non-volatile memory devices comprises a semiconductor device configured to individually address said at least one microstructure non-volatile memory device.

17. The passive microdosimetry system as in claim 16, wherein said semiconductor device comprises an erasable programmable read only memory chip.

18. The passive microdosimetry system as in claim 16, wherein said semiconductor device is configured to permit the individual measurement of said at least one microstructure non-volatile memory device by said measurement device.

19. The passive microdosimetry system as in claim 15, wherein said measuring mechanism is configured to measure said generated charge without destroying the post-irradiation charge stored on said at least one microstructure non-volatile devices.

20. The passive microdosimetry system as in claim 15, wherein each of said microstructure sensitive volumes is generally not more than one cubic micrometer.

21. The passive microdosimetry system as in claim 20, wherein each of said microstructure sensitive volumes is approximately 0.1 micrometers by 1.0 micrometer by 100 angstroms thick with respect to the incidence of said radiation.

22. The passive microdosimetry system as in claim 15, wherein said measurement device further comprises a charging device for charging said at least one microstructure non-volatile memory device to said predetermined initial charge.

23. The passive microdosimetry system as in claim 22, wherein said predetermined initial charge is stored on an electrically insulated gate within each said at least one microstructure non-volatile memory device.

24. The passive microdosimetry system as in claim 22, wherein said predetermined initial charge on said at least one microstructure non-volatile memory device is set relative to a known threshold charge such that traversal of said known threshold charge from said predetermined initial charge causes said at least one microstructure non-volatile memory device to change state.

25. The passive microdosimetry system as in claim 24, wherein said at least one microstructure non-volatile memory device is configured such that said generated charge alters said predetermined initial charge towards said threshold charge.

26. The passive microdosimetry system as in claim 25, wherein said at least one microstructure non-volatile memory device is configured such that the difference between said altered charge and said predetermined initial charge corresponds to the energy deposited by incident radiation on said at least one microstructure non-volatile memory device during exposure of said at least one detector array to incident radiation.

27. The passive microdosimetry system as in claim 24, wherein said measuring mechanism is configured to measure the charge alteration due to said charge generated by incident radiation by changing the post-irradiation charge stored on said at least one microstructure non-volatile memory device at a known rate toward said threshold charge and determining the time required for said at least one microstructure non-volatile memory device to change state.

28. The passive microdosimetry system as in claim 27, wherein said measuring mechanism is configured to change said post-irradiation charge on said at least one microstructure non-volatile memory device by optical application of ultraviolet light to said at least one detector array.

29. The passive microdosimetry system as in claim 27, wherein said measuring mechanism is configured to change said post-irradiation charge on said at least one microstructure non-volatile memory device by the application of electrically generated tunnelling current to said at least one microstructure non-volatile memory device.

30. The passive microdosimetry system as in claim 27, wherein said measuring mechanism is configured to change said post-irradiation charge on said at least one microstructure non-volatile memory device by the imposition of an electric field to said at least one microstructure non-volatile memory device in opposition to a stable state electric field maintained by said at least one microstructure non-volatile memory device.

31. The passive microdosimetry system as in claim 15, wherein said qualitative analyzing device is configured to convert said generated charge into an estimate of the number of events occurring within discrete energy bands within the measured area of said at least one detector array of microstructure non-volatile memory devices.

32. The passive microdosimetry system as in claim 31, wherein said qualitative analyzing device is configured to apply sensitive volume dependent weighting factors to said estimate according to said discrete energy bands, said weighting factors correlating to known energy ranges within which known ionizing particles, in sensitive volumes comparable to said sensitive volumes of said microstructure non-volatile memory devices, deposit energy so that a spectral analysis of the complex radiation field is generated.

33. The passive microdosimetry system as in claim 15, wherein said measuring mechanism is furthermore configured to measure the spatial distribution of said generated charge depositions throughout the measured area of said at least one detector array of microstructure non-volatile memory devices.

34. The passive microdosimetry system as in claim 33, wherein said qualitative analyzing device is configured to convert said generated charge deposition and distribution into an estimate of the number of events occurring within said measured area of said at least one detector array of microstructure non-volatile memory devices within discrete energy bands.

35. The passive microdosimetry system as in claim 34, wherein said qualitative analyzing device is configured to apply sensitive volume dependent weighting factors to said estimate according to said discrete energy bands, said weighting factors correlating to known energy ranges within which known ionizing particles, in sensitive volumes comparable to said sensitive volumes of said microstructure non-volatile memory devices, deposit energy so that a spectral analysis of the complex radiation field is generated.

36. The passive microdosimetry system as in claim 15, wherein said system is configured as a personal sized radiation microdosimetry device.

37. The passive microdosimetry system as in claim 15, wherein said system is configured as an area monitor.

38. The passive microdosimetry system as in claim 37, wherein said system is configured as an area monitor for a space platform.

39. A method for qualitatively analyzing a complex incident radiation field, comprising the step of:

subjecting to the radiation field a detector array comprised of a plurality of microstructure non-volatile memory devices having a corresponding plurality of associated microstructure sensitive volumes;

individually measuring the charge deposition on at least one of said microstructure non-volatile devices, said charge deposition being generated responsive to the incident radiation within the corresponding microstructure sensitive volume of said at least one microstructure non-volatile memory device; and

outputting said charge deposition for conversion to a qualitative analysis of the complex radiation field.

40. The method as in claim 39, further comprising the steps of:

converting said charge deposition into an estimate of the number of events within discrete energy bands occurring within a measured area of said array of microstructure non-volatile memory devices; and

translating said estimate into a qualitative analysis of the complex radiation field.

41. The method as in claim 40, wherein said qualitative analysis comprises a spectral analysis.

42. The method as in claim 40, wherein said measuring step further comprises the step of measuring the spatial charge distribution throughout said measured area and wherein said converting step converts said charge deposition and said spatial charge distribution to said estimate.

43. The method as in claim 40, wherein said translating step further comprises the step of applying sensitive volume dependent weighting factors to said estimate according to said discrete energy bands, said weighting factors correlating to known energy ranges within which known ionizing particles, in sensitive volumes comparable to said sensitive volumes of said microstructure non-volatile memory devices, deposit energy so that a spectral analysis of the complex radiation field is generated.

44. The method as in claim 42, wherein said translating step further comprises the step of applying sensitive volume dependent weighting factors to said estimate according to said discrete energy bands, said weighting factors correlating to known energy ranges within which known ionizing particles, in sensitive volumes comparable to said sensitive volumes of said microstructure non-volatile memory devices, deposit energy so that a spectral analysis of the complex radiation field is generated.

45. The method as in claim 39, wherein said measuring step preserves the stored charge on said at least one microstructure non-volatile memory device.

46. The method as in claim 45, further comprising the step of charging, prior to said subjecting step, said at least one microstructure non-volatile memory device of said array to a predetermined initial charge set relative to a known threshold charge such that traversal of said known threshold charge from said predetermined initial charge causes said at least one microstructure non-volatile memory device to change state and wherein said predetermined initial charge may be altered towards said threshold charge during said subjecting step responsive to incident radiation;

and

wherein said measuring step is further comprised of the steps of repeatedly reading the state of, and decrementing by a predetermined value the control gate bias of, each of said at least one microstructure non-volatile memory devices within a measured area of said array of microstructure non-volatile memory devices and determining the control gate bias at which each said microstructure non-volatile memory device within said measured area changes state.

47. The method as in claim 46, further comprising the steps of:

converting said control gate bias value at which each said microstructure non-volatile memory device within said measured area changes state into an estimate of the number of events within discrete energy bands occurring within said measured area; and

translating said estimate into a qualitative analysis of the complex radiation field.

48. The method as in claim 47, wherein said qualitative analysis comprises a spectral analysis.

49. The method as in claim 39, further comprising the step of charging, prior to said subjecting step, said at least one microstructure non-volatile memory device of said array to a predetermined initial charge, said predetermined initial charge being altered during said subjecting step responsive to said incident radiation.

50. The method as in claim 49, wherein said predetermined initial charge is set relative to a known threshold charge such that traversal of said known threshold charge from said predetermined initial charge causes said at least one microstructure non-volatile memory device to change state.

51. The method as in claim 50, wherein said measuring step further comprises the step of changing the post-irradiation charge on said at least one microstructure non-volatile memory device at a know rate towards said threshold charge and determining the time required for said at least one microstructure non-volatile memory device to charge state.

52. The method as in claim 51, wherein said measuring step further comprises the step of detecting, prior to changing said post-irradiation charge, any said at least one microstructure non-volatile memory device having changed state responsive to incident radiation.

53. The method as in claim 51, wherein said post-irradiation charge is changed by optically applying ultraviolet light to said detector array.

54. The method as in claim 51, wherein said post-irradiation charge is changed by applying electrically generated tunnelling current to said at least one microstructure non-volatile memory device.

55. The method as in claim 51, wherein said post-irradiation charge is changed by imposing an electric field to said at least one microstructure non-volatile memory device in opposition to a stable state electric field maintained by said at least one microstructure non-volatile memory device.

56. The method as in claim 39, further comprising the step of shielding said at least one microstructure non-volatile memory device with shielding material so that said at least one microstructure non-volatile memory device simulates specific biological tissue.

57. A passive microdosimetry system for qualitatively analyzing radiation incident thereof in a complex radiation field, comprising:

at least one detector array of microstructure non-volatile memory device comprising a semiconductor device configured to individually address at least one of said microstructure non-volatile memory devices, each of said at least one microstructure non-volatile memory device being configured to store a predetermined initial charge thereon and defining a microstructure sensitive volume within which charge is generated responsive to incident radiation such that said generated charge individually and measurably alters said predetermined initial charge stored on said at least one microstructure non-volatile memory device;

measurement device operatively associated with said at least one detector array, comprising

communicating device for communicating with said at least one detector array, and

measuring mechanism for measuring said charge generated on said at least one microstructure non-volatile memory devices within a measured area of said at least one detector array; and

a qualitative analyzing device operatively associated with said measurement device for converting said generated charge into an estimate of the number of events occurring within discrete energy bands within said measured area and applying sensitive volume dependent weighting factors to said estimate according to said discrete energy bands, said weighting factors correlating to known energy ranges within which known ionizing particles, in sensitive volumes comparable to said sensitive volumes of said microstructure non-volatile memory devices, deposit energy so that a spectral analysis of the complex radiation field is generated.

58. The passive microdosimetry system as in claim 57, wherein each microstructure sensitive volume of said at least one microstructure non-volatile memory device is generally not more than one cubic micrometer.

59. The passive microdosimetry system as in claim 57, wherein said predetermined initial charge on said at least one microstructure non-volatile memory device is set relative to a known threshold charge such that traversal of said known threshold charge from said predetermined initial charge causes said at least one microstructure non-volatile memory device to change state and wherein said at least one microstructure non-volatile memory device is configured such that said generated charge alters said predetermined initial charge towards said threshold charge.

60. The passive microdosimetry system as in claim 59, wherein said measuring mechanism is configured to measure said charge alteration due to incident radiation by changing the post-irradiation charge on said at least one microstructure non-volatile memory device at a known rate towards said threshold charge and determining the time required for said at least one microstructure non-volatile memory device to change state.

61. The passive microdosimetry system as in claim 57, wherein said system is configured as a personal sized radiation microdosimetry device.

62. The passive microdosimetry system as in claim 57, wherein said system is configured as an area monitor.

63. A method for qualitatively analyzing a complex incident radiation field, comprising the steps of:

charging to a predetermined initial charge at least one microstructure non-volatile memory device of at least one detector array of microstructure non-volatile memory devices each having an associated microstructure sensitive volume, wherein said predetermined initial charge is set relative to a known threshold charge so that the traversal of said known threshold charge from said predetermined initial charge causes said at least one microstructure non-volatile memory device to change state;

subjecting to the radiation field said at least one detector array; and

measuring the generated charge on a measured area of said detector array, said generated charge being responsive to incident radiation within said microstructure sensitive volumes of the at least one microstructure non-volatile memory devices within said measured area, by changing the post-irradiation charge on at least one of said microstructure non-volatile memory device at a known rate toward said threshold charge and determining the time required for each said at least one microstructure memory device to change state.

64. The method as in claim 63, further comprising the steps of:

converting said generated charge into an estimate of the number of events occurring within discrete energy bands within said measured area; and

applying sensitive volume dependent weighting factors to said estimate according to said discrete energy bands, said weighting factors correlating to known energy ranges within which known ionizing particles, in sensitive volumes comparable to said sensitive volumes of said microstructure non-volatile memory devices, deposit energy so that a spectral analysis of the complex radiation field is generated.

65. The method as in claim 63, further comprising the step of detecting, prior to said changing step, any said at least one microstructure non-volatile memory device having changed state responsive to incident radiation.

66. The method as in claim 63, further comprising the step of measuring the spatial charge distribution throughout said measured area and wherein said charge deposition and said spatial charge distribution are converted to said estimate in said converting step.