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Health Physics. 2 : Radiation Measurements. 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”.

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health physics

Health Physics

2: Radiation Measurements

introduction
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”.

detection of radiation
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”.

indirect ionization by photon
Indirect Ionization by Photon

Ejected

Electron

Incoming

Photon

two basic types of radiation measurements in health physics
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”.

external radiation hazard 1
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”.

external radiation hazard 2
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”.

internal radiation hazard 1
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”.

internal radiation hazard 2
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”.

types of radiation monitoring
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”.

ideal radiation detector
“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”.

real radiation detector
“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”.

energy dependence of gamma survey meter
Energy Dependence of Gamma Survey Meter

Page(s): 153 to 154

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

f factor rads roentgen
f-Factor (rads/Roentgen)

Page(s):

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

radiation instruments

Radiation Instruments

GMs from 1962 to 1999

1985

1999

1970

1962

instruments

Instruments

Example: GM Model

gm survey meter
GM Survey Meter
  • Dial in mR/hr
  • Battery check
electronic personal dosimeter epd
Electronic Personal Dosimeter(EPD)

Page(s): at end of handout

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

radiation instruments24

Radiation Instruments

Security Gates

gas detectors
Gas Detectors
  • Ionization Chambers
  • Proportional Counters
  • Geiger-Mueller Counters (GMs)

Page(s): 111 to 125

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

gas filled detectors
Gas-Filled Detectors

Voltage Source

Incident

Ionizing

Radiation

+

+

+

Electrical

Current

Measuring

Device

-

-

-

Anode +

Cathode -

ionization chamber
Ionization Chamber

Page(s): 113

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

ionization chamber29
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”.

condenser type dosimeter
Condenser Type Dosimeter

Page(s): 115

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

direct reading dosimeter drd
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 handout:”Chapter 8: Radiation Measurements”.

gas multiplication
Gas Multiplication

Page(s): 117 to 118

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

secondary ions

proportional counters
Proportional Counters

Page(s): 118 to 119

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

windowless

proportional counter
Proportional Counter
  • Characteristics
    • Energy information preserved
    • Particles yield larger pulses than photons
    • Differentiate particle exposure in presenceof 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”.

geiger plateau
Geiger Plateau

Page(s): 120

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

geiger mueller counter
Geiger-Mueller Counter

Page(s): 119 to 124

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

gm counter
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”.

scintillation detectors
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”.

photon interaction with nai tl crystal
Photon Interaction with NaI(Tl) Crystal

Page(s): 126 to 127

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

nai tl pmt assembly
NaI(Tl) – PMT Assembly

Page(s): 127

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

scintillator characteristics
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”.

phosphor pmt assembly
Phosphor- PMT Assembly

Page(s): 127

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

photomultiplier tube pmt
Photomultiplier Tube (PMT)

Page(s): 127 to 129

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

electron multiplication in pmt
Electron Multiplication in PMT

Page(s): 127 to 129

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

counting chain 1
Counting Chain (1)

Page(s): 129

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

discriminator action
Discriminator Action

Page(s): 130

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

counting chain 2
Counting Chain (2)

Page(s): 131

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

counting chain 3
Counting Chain (3)

Page(s): 132

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

co 60 energy spectrum from nai tl detector
Co-60 Energy Spectrum from NaI(Tl) Detector

Page(s): 136

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

energy spectrum from nai tl detector
Energy Spectrum from NaI(Tl) Detector

Page(s): 136

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

energy resolution fwhm
Energy Resolution (FWHM)

Page(s): 136

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

energy transfer in phosphor
Energy Transfer in Phosphor

Page(s): 125 to 127

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

photoelectric effect
Photoelectric Effect

Page(s): 125 to 127

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

well counter
Well Counter

Page(s):

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

liquid scintillation counter 1
Liquid Scintillation Counter (1)

Page(s): 132

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

liquid scintillation counter 2
Liquid Scintillation Counter (2)

Page(s): 132

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

liquid scintillation counter 3
Liquid Scintillation Counter (3)

Page(s): 132

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

liquid scintillation
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”.

scintillators for alpha and beta particles
Scintillators for Alpha and Beta Particles

Page(s): 134 to 135

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

films and tlds
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”.

film dosimeter calibration curve
Film Dosimeter Calibration Curve

Page(s): 138 to 139

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

film dosimeter energy dependence
Film Dosimeter: Energy Dependence

Page(s): 140 to 141

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

tld x ray sensitivity of lif
TLD: X-ray Sensitivity of LiF

Page(s): 143 to 147

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

special detectors
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”.

semiconductor detector
Semiconductor Detector

Page(s): 147 to 149

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

Si or Ge

p-layer

n-layer

detector cooling
Detector Cooling

Page(s): 147 to 149

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

neutron tld with li 6 and li 7 2
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”.

neutron tld with li 6 and li 7 1
Neutron TLD with Li-6 and Li-7 (1)

Page(s): 149 to 150

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

damage track neutron dosimeter
Damage Track Neutron Dosimeter

Page(s): 149 to 151

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

bubble neutron dosimeter
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”.

use of radiation instruments
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”.

energy dependence of gamma survey meter77
Energy Dependence of Gamma Survey Meter

Page(s): 153 to 154

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

rate meter response time constant
Rate Meter Response (Time Constant)

Page(s): 152 to 153

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

master
Master

Page(s): 107 to

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

master86
Master

Page(s): 107 to

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

master87
Master

Page(s): 107 to

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

master88
Master

Page(s): 107 to

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

slide90

BASIC KNOWLEDGE- DOSE -

  • The Dose From Being Exposed to Cosmic and Machine Produced Radiation Depends on:
  • Time
  • Distance
  • Shielding
energy response of ionization chamber
Energy Response of Ionization Chamber

Page(s): 116 to 117

Page numbers refer to handout:”Chapter 8: Radiation Measurements”.

references
References
  • Nuclear Regulatory Commission Home Page: www.nrc.gov
      • teachers corner@www.nrc.gov/NRC/teachers.html
      • students corner@www.nrc.gov/NRC/STUDENTS/students.html
  • Nuclear Energy Institute Home Page: www.nei.org
      • science club@ www.nei.org/scienceclub/index.html
  • Health Physics Society Home Page: www.hps.org
      • www.hps.org/publicinformation/radfactsheets/