Health%20Physics

1
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 handoutChapter 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 handoutChapter 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 handoutChapter 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 handoutChapter 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 handoutChapter 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 handoutChapter 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 handoutChapter 8
  Radiation Measurements.

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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 handoutChapter 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 handoutChapter 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 handoutChapter 8
  Radiation Measurements.

14
Energy Dependence of Gamma Survey Meter

• Page(s) 153 to 154
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

15
f-Factor (rads/Roentgen)

• Page(s)
• Page numbers refer to handoutChapter 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 handoutChapter 8
  Radiation Measurements.

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Electronic Personal Dosimeter(EPD)
Skin dose
Body dose
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Radiation Instruments

• Car Gate

22
Radiation Instruments

• Conveyor

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Radiation Instruments

• Truck Monitor

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Radiation Instruments

• Security Gates

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Gas Detectors

• Ionization Chambers
• Proportional Counters
• Geiger-Mueller Counters (GMs)
• Page(s) 111 to 125
• Page numbers refer to handoutChapter 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 handoutChapter 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 handoutChapter 8
  Radiation Measurements.

30
Condenser Type Dosimeter

• Page(s) 115
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Direct Reading Dosimeter (DRD)
Natural leakage of 5-10 mR/day Keep control
DRD in desk! Do not drop!

• Page(s) 115-116
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

32
Gas Multiplication

• Page(s) 117 to 118
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

secondary ions
33
Proportional Counters

• Page(s) 118 to 119
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

windowless
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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 handoutChapter 8
  Radiation Measurements.

35
Geiger Plateau

• Page(s) 120
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Geiger-Mueller Counter

• Page(s) 119 to 124
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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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 handoutChapter 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 handoutChapter 8
  Radiation Measurements.

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Photon Interaction with NaI(Tl) Crystal

• Page(s) 126 to 127
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

41
NaI(Tl) PMT Assembly

• Page(s) 127
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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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 handoutChapter 8
  Radiation Measurements.

43
Phosphor- PMT Assembly

• Page(s) 127
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

44
Photomultiplier Tube (PMT)

• Page(s) 127 to 129
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

45
Electron Multiplication in PMT

• Page(s) 127 to 129
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Counting Chain (1)

• Page(s) 129
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Discriminator Action

• Page(s) 130
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Counting Chain (2)

• Page(s) 131
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Counting Chain (3)

• Page(s) 132
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

50
Co-60 Energy Spectrum from NaI(Tl) Detector

• Page(s) 136
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Energy Spectrum from NaI(Tl) Detector

• Page(s) 136
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Energy Resolution (FWHM)

• Page(s) 136
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Energy Transfer in Phosphor

• Page(s) 125 to 127
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Photoelectric Effect

• Page(s) 125 to 127
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

55
Well Counter

• Page(s)
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Liquid Scintillation Counter (1)

• Page(s) 132
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Liquid Scintillation Counter (2)

• Page(s) 132
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Liquid Scintillation Counter (3)

• Page(s) 132
• Page numbers refer to handoutChapter 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 handoutChapter 8
  Radiation Measurements.

60
Scintillators for Alpha and Beta Particles

• Page(s) 134 to 135
• Page numbers refer to handoutChapter 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 handoutChapter 8
  Radiation Measurements.

62
Film Dosimeter Calibration Curve

• Page(s) 138 to 139
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

63
Film Dosimeter Energy Dependence

• Page(s) 140 to 141
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

64
Single Images
65
TLD X-ray Sensitivity of LiF

• Page(s) 143 to 147
• Page numbers refer to handoutChapter 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 handoutChapter 8
  Radiation Measurements.

68
Semiconductor Detector

• Page(s) 147 to 149
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

Si or Ge
p-layer
n-layer
69
Detector Cooling

• Page(s) 147 to 149
• Page numbers refer to handoutChapter 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 handoutChapter 8
  Radiation Measurements.

72
Neutron TLD with Li-6 and Li-7 (1)

• Page(s) 149 to 150
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

73
Damage Track Neutron Dosimeter

• Page(s) 149 to 151
• Page numbers refer to handoutChapter 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 handoutChapter 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 handoutChapter 8
  Radiation Measurements.

76
Single Images
77
Energy Dependence of Gamma Survey Meter

• Page(s) 153 to 154
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

78
Rate Meter Response (Time Constant)

• Page(s) 152 to 153
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Single Images
80
Single Images
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Master

• Page(s) 107 to
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Master

• Page(s) 107 to
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Master

• Page(s) 107 to
• Page numbers refer to handoutChapter 8
  Radiation Measurements.

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Master

• Page(s) 107 to
• Page numbers refer to handoutChapter 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 handoutChapter 8
  Radiation Measurements.

92
References

• Nuclear Regulatory Commission Home Page
  www.nrc.gov
• teachers corner_at_www.nrc.gov/NRC/teachers.html
• students corner_at_www.nrc.gov/NRC/STUDENTS/students.
  html
• Nuclear Energy Institute Home Page www.nei.org
• science club_at_ www.nei.org/scienceclub/index.html
• Health Physics Society Home Page www.hps.org
• www.hps.org/publicinformation/radfactsheets/