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Health Physics

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

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  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 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

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

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

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

  28. 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”.

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

  30. 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”.

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

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

  33. 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”.

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

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

  36. 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”.

  37. Single Images

  38. 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”.

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

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

  41. 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”.

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

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

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

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

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

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

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

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

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