1. 2: Radiation Measurements
Health Physics
2: Radiation Measurements

2. Introduction Radiation not detected with our senses
Need detectors to confirm presence
of radiation
Avoid over – exposures (reddening of skin - 3Gy)
Page(s): 107
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

3. Detection of Radiation
Made possible by its interaction with matter
(solid, liquid gas)
Ionization (electrical charges), excitation
Direct (charged particels) and indirect (photons, neutrons) ionization
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

4. Indirect Ionization by Photon
Ejected
Electron
Incoming
Photon

5. Two Basic Types of Radiation Measurements in Health Physics:
External radiation hazard
measure exposure rate, dose or dose-rate
Internal radiation hazard
measure contamination in working area, bioassay
Page(s): 107 to 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

6. Penetration Power of Radiation

7. External Radiation Hazard (1)
Discriminate between particles and gamma radiation using probe - shield
Measure exposure rate (X/t) or dose rate
(mR per hour, mSv per hour)
Measure dose (integrate dose rate, dosimeter)
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

8. External Radiation Hazard (2)
continued …
X-rays, gamma radiation, neutrons
Energetic beta particles (P-32: 1.7 MeV)
Neutrons (from accelerators, cyclotrons), fast and thermal neutrons
Page(s): 107 to 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

9. Internal Radiation Hazard (1)
Measure contamination in working area
(surface, air, water) “wipe tests” (betas)
Whole-body counter (gamma emitters)
Bioassays (thyroid assay, urine analysis)
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

10. Internal Radiation Hazard (2)
continued …
Alpha or beta particles when inhaled or ingested
(e.g. tritium vapors in power stations containing
H-3 with 18keV betas)
Boneseekers with long half-lives when inhaled or ingested
(Sr-90: 0.5MeV betas, Pu-239 : 5MeV alphas)
Any radioactive material that enters the body in large amounts
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

11. Types of Radiation Monitoring
Area and survey monitoring (portable or fixed detectors)
Technique or procedure monitoring
(DRDs or EPDs)
Personal Monitoring (TLD “badges”)
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

12. “Ideal” Radiation Detector
Responds to one radiation type only
Includes radiation quality factor, wR
Uniform energy response
Gives equivalent dose (H) or equivalent dose rate
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

13. “Real” Radiation Detector
Need to discriminate between particles and gamma radiation using probe - shield
Non-uniform energy response
Often gives exposure rate (X / t) only
(Milli-Roentgen per hour)
Page(s): 108
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

14. Energy Dependence of Gamma Survey Meter
Page(s): 153 to 154
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

15. f-Factor (rads/Roentgen)
Page(s):
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

16. Radiation Instruments
GMs from 1962 to 1999
1985
1999
1970
1962

17. Instruments
Example: GM Model

18. GM Survey Meter
Dial in mR/hr
Battery check

19. Electronic Personal Dosimeter(EPD)
Page(s): at end of handout
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

20. Electronic Personal Dosimeter(EPD)
Skin dose
Body dose

21. Radiation Instruments
Car Gate

22. Radiation Instruments
Conveyor

23. Radiation Instruments
Truck Monitor

24. Radiation Instruments
Security Gates

26. Gas Detectors Ionization Chambers Proportional Counters
Geiger-Mueller Counters (GMs)
Page(s): 111 to 125
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

27. Gas-Filled Detectors Voltage Source Incident Ionizing Radiation + + +
Electrical
Current
Measuring
Device - - -
Anode +
Cathode -

28. Ionization Chamber Page(s): 113
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

29. Ionization Chamber Characteristics
rel. low sensitivity (ideal as control instrument in high field of nuclear reactors)
measures exposure rates up to 1000 R / min
Page(s): 112 to 117
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

30. Condenser Type Dosimeter
Page(s): 115
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

31. Direct Reading Dosimeter (DRD)
Natural leakage of
5-10 mR/day
Keep control DRD in desk!
Do not drop!
Page(s):
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

32. Gas Multiplication secondary ions Page(s): 117 to 118
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.
secondary ions

33. Proportional Counters
Page(s): 118 to 119
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.
windowless

34. Proportional Counter Characteristics Energy information preserved
Particles yield larger pulses than photons
Differentiate particle exposure in presence of photons
Detects thermal neutrons via n-alpha reaction if tube lined with Boron or if BF3 is used as filling gas
Page(s): 117 to 119
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

35. Geiger Plateau Page(s): 120
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

36. Geiger-Mueller Counter
Page(s): 119 to 124
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

37. GM Counter Characteristics large dead time (~ 100μs), saturation
has no energy info.
high sensitivity (100% for each ionizing event)
measures low exposure rates (~0.1 mR / hr)
Page(s): 112 to 117
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

38. Single Images

39. Scintillation Detectors
Phosphors (NaI(Tl), CsF, BGO, LSO)
Photomultiplier Tube (PMT)
dynodes, counting chain, spectra
Liquid Scintillation Counting (“wipes”)
Page(s): 125 to 137
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

40. Photon Interaction with NaI(Tl) Crystal
Page(s): 126 to 127
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

41. NaI(Tl) – PMT Assembly Page(s): 127
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

42. Scintillator Characteristics
Phosphors (NaI(Tl), CsF, BGO, LSO)
Photoelectric interaction ~ Z4
NaI(Tl): reference, decay const. ~ 1μs
CsF : faster than NaI(Tl), TOF PET
BGO : slower but more efficient, PET
LSO : very fast (~1ns), high res. PET
Page(s): 125 to 137
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

43. Phosphor- PMT Assembly
Page(s): 127
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

44. Photomultiplier Tube (PMT)
Page(s): 127 to 129
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

45. Electron Multiplication in PMT
Page(s): 127 to 129
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

46. Counting Chain (1) Page(s): 129
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

47. Discriminator Action Page(s): 130
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

48. Counting Chain (2) Page(s): 131
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

49. Counting Chain (3) Page(s): 132
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

50. Co-60 Energy Spectrum from NaI(Tl) Detector
Page(s): 136
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

51. Energy Spectrum from NaI(Tl) Detector
Page(s): 136
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

52. Energy Resolution (FWHM)
Page(s): 136
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

53. Energy Transfer in Phosphor
Page(s): 125 to 127
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

54. Photoelectric Effect Page(s): 125 to 127
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

55. Well Counter
Page(s):
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

56. Liquid Scintillation Counter (1)
Page(s): 132
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

57. Liquid Scintillation Counter (2)
Page(s): 132
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

58. Liquid Scintillation Counter (3)
Page(s): 132
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

59. Liquid Scintillation
Scintillator in intimate contact with radiation source (mainly alphas and betas)
Solvent (toluene) and solute(POPOP)
Efficiency for alphas and betas: 50 to 100%
Correct for quenching effects (chemical, color)
Wave length shifter to match photocathode response
Page(s): 132 to 133
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

60. Scintillators for Alpha and Beta Particles
Page(s): 134 to 135
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

61. Films and TLDs Film dosimeters (badges) body, skin, wrist monitoring
Thermoluminescent Dosimeters (TLDs)
LiF, Al2O3 in many shapes: finger ring TLD
very sensitive, linear response
neutron response possible (Li-6, Li-7)
Page(s): 138 to 147
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

62. Film Dosimeter Calibration Curve
Page(s): 138 to 139
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

63. Film Dosimeter: Energy Dependence
Page(s): 140 to 141
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

64. Single Images

65. TLD: X-ray Sensitivity of LiF
Page(s): 143 to 147
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

66. Single Images

67. Special Detectors Semiconductor detectors (nuclear diodes)
Si(Li), Ge(Li), Ge(hyperpure)
Thermoluminescent neutron dosimeters
Li-6 vs. Li-7
Damage track neutron dosimeters
Bubble neutron dosimeters
Page(s): 147 to end of handout
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

68. Semiconductor Detector
Page(s): 147 to 149
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.
Si or Ge
p-layer
n-layer

69. Detector Cooling Page(s): 147 to 149
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

70. Single Images

71. Neutron TLD with Li-6 and Li-7 (2)
Li-6 (7.5%): responds to both gammas and to slow neutrons by n- alpha reaction enrich!
Li-7 (92.5%): only responds to gammas
Polyethylene slows down fast neutrons
Cd captures slow
neutrons
Page(s): 149 to 150
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

72. Neutron TLD with Li-6 and Li-7 (1)
Page(s): 149 to 150
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

73. Damage Track Neutron Dosimeter
Page(s): 149 to 151
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

74. Bubble Neutron Dosimeter
Elastic polymer with suspended
droplets of superheated liquid
When struck by radiation,
droplets form gas bubble
Bubbles remain fixed in polymer
for permanent visual record
Calibration in “bubbles per mrem”
or “bubbles per Sv”
Page(s): end of handout
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

75. Use of Radiation Instruments
Detection and geometric efficiency
Time constant and dead time
Directional response
Operational checks (battery!), calibration
Page(s): 151 to 156
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

76. Single Images

77. Energy Dependence of Gamma Survey Meter
Page(s): 153 to 154
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

78. Rate Meter Response (Time Constant)
Page(s): 152 to 153
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

79. Single Images

80. Single Images

85. Master
Page(s): 107 to
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

86. Master
Page(s): 107 to
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

87. Master
Page(s): 107 to
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

88. Master
Page(s): 107 to
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

89. Shielding

90. BASIC KNOWLEDGE - DOSE -
The Dose From Being Exposed to Cosmic and Machine Produced Radiation Depends on:
Time
Distance
Shielding

91. Energy Response of Ionization Chamber
Page(s): 116 to 117
Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

92. References Nuclear Regulatory Commission Home Page: www.nrc.gov
teachers
students
Nuclear Energy Institute Home Page:
science
Health Physics Society Home Page: