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Radiation Exposure and Risk Assessment

Radiation Exposure and Risk Assessment. Maximum Permissible Dose General Public. Whole Body 1 mSv/year Skin 50 mSv/year Hands Feet 50 mSv/year Lens of the eye 15 mSv/year. Nuclear Energy Workers. Who is an NEW?

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Radiation Exposure and Risk Assessment

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  1. Radiation Exposure and Risk Assessment

  2. Maximum Permissible DoseGeneral Public Whole Body 1 mSv/year Skin 50 mSv/year Hands Feet 50 mSv/year Lens of the eye 15 mSv/year

  3. Nuclear Energy Workers Who is an NEW? A worker who has a REASONABLE PROBABILITY of exceeding the 1 mSv limit to the general public. Registered with the RSO.

  4. Maximum Permissible Dose Whole Body 50 mSv/year Skin 500 mSv/year Hands Feet 500 mSv/year Lens of the eye 150 mSv/year Nuclear Energy Worker (CNSC)

  5. Radiation Exposure of Women Nuclear Energy Workers Whole Body Limit may not exceed annual limit of 5 mSv • Radiation exposure at the surface of the abdomen may not exceed 4 mSv following declaration of pregnancy • Badges changed quarterly Inform, Review, Reassign, Restrict

  6. Radiation CANNOT be: Felt Heard Tasted Smelled Seen So…how do you know you have had enough?

  7. Dosimetry • External Personal Monitoring • Thermoluminescent dosimeters • Lithium Fluoride Crystals • Optically read dosimeters : LUXEL • Skin Dose • Body Dose • Internal Personal Monitoring • Bioassay • Urine, saliva, sweat, feces • Thyroid • Difficult -distribution variability

  8. Thermoluminescent Dosimeters Landauer Health Canada

  9. Optically Read Dosimeters (Landauer)

  10. Personal Alarm Dosimeter

  11. Who MUST wear a TLD? A NEW who has a REASONABLE PROBABILITY of receiving a radiation exposure greater than 5mSv/year (CNSC) 1mSv/year – UBC action level

  12. How do I estimate my dose?Will I need to be monitored?

  13. External Exposure Estimate Where: X = Dose (mSv)  = Specific Gamma Ray Constant A = Activity (MBq) t = Time (hours) d = Distance from Source (cm)

  14. X = Total Dose t = 44 hours  = 3.24 (mSv*cm2)/(h*MBq) at 1 cm A = 185 MBq d = 35 cm What is the radiation dose received by a graduate student working with 185 MBq of Na-22 for two hours per day for 22 days at a distance of 35 cm from the source and using no shielding?

  15. X = ΓAt (D)2 X = (3.24) (mSv*cm2)/(h*MBq) (185 MBq) (44h) (35cm)2 X = 21.5 mSv

  16. Who SHOULD NOT wear a TLD? • A NEW who has only a • REMOTEPOSSIBILITY of receiving a • radiation exposure greater than 1mSv/yr. • Personnel working with low energy betas • such as S-35, C-14 and H-3.

  17. External Exposure Estimate For gamma radiation

  18. ESTIMATION OF EXTERNAL β-RADIATION DOSE NOT IN CONTACT WITH SKIN • Rule of thumb, valid over a wide range of beta energies Activity (Bq) Distance from source (m) Dose Rate (Sv/hr) • Assumes point source and no attenuation to air or source material • Expect large errors beyond 1 m (overestimates absorbed dose)

  19. Internal Exposure • Iodine – 125 , 131 Concentrate in thyroid • *CNSC regulation* • Contact HSE before using Iodine 125, 131 • Contact during planning stage • Specific monitoring protocols are required

  20. Question? • A salesman is showing you a new piece of equipment which has a radiation trefoil on the side. He assures you that the equipment is safe because it contains an alpha emitter that has been shown to produce 4 roentgens and is in a lead sealed casing. He also tells you that other users only report about 0.9 mS per year…Will you buy it?

  21. Section 3 - *B.E.I.R • Biological Effects of Ionizing • Radiation *U.S. National Academy of Sciences Reports

  22. “Radium Girls”

  23. Early martyrs Radium Dial Painters Tuberculosis Patients Survivors of Atomic Bombings Ankylosing Spondylitis Patients Uranium Miners – Elliot Lake, Ont. Radiation Institute of Canada B.E.I.R. Human Experience

  24. Effects – Chronic vs. Acute • Chronic: repeated doses of low levels of radioactive materials • Acute: single or short term doses at higher levels • Often use one to help understand the other

  25. somatic if they become manifest in the exposed person Non-reproductive cells genetic if they affect their descendants. Reproductive cells Effects of Radiation: Somatic or Genetic

  26. Age effects are important, age independent risk estimates may be inappropriate. Diet, genetics, lifestyle factors can all affect outcome Synergistic effects may be important eg. Uranium miners : smoking Somatic Effects and Risk Factors

  27. Cancers induced by radiation are indistinguishable from those caused naturally Solid tumours such as breast, lung, thyroid and GI are greater numerically than leukemia Risk is greater for women - breast and thyroid cancer Cancer complex disease – no guarantees

  28. 30 – 100 Trillion Cells at Risk Different Cell Types Different Cell Cycle Different Cell Targets

  29. End Effect of Radiation Organelle death Cell death Cell healing Chromosome loss Gene loss Gene rearrangement

  30. DNA Damage Single Strand Break Double Strand Break* Change or Loss of Base Bond Breakage- Uncoiling Intra-Helix Crosslinking Inter-Helix Crosslinking Inter-Protein Crosslinking

  31. Dicentric chromosomes induced by radiation exposure Unexposed Exposed

  32. Atomic bomb victims* *Chernobyl Increasing Radiation Dose LNT model: linear, no threshold Incidence of effects

  33. Incidence of Radium-Induced Malignant Tumors Incidence Estimated Maximum Radium Burden in Bq

  34. Atomic bomb victims* Threshold model *Chernobyl “Normal Exposure”? Incidence of effects Radiation Hormesis Increasing Radiation Dose

  35. Where does our radiation dose come from?

  36. Sky100,000 Cosmic Neutrons /hr 400,000 Cosmic Gamma rays/hr Soil and Building 200,000,000 Gamma rays/hr Air30,000 decays/hr Alpha, Beta, Gamma Food and Drink 15,000,000 K- 40/hr 7,000 Uranium/hr 12,240,000 C-14/hr Natural Sources:

  37. Dose Rates – Cosmic Rays AltitudeμSv/hr 10 Km 5 6.7 Km 1 Whistler 0.1 Sea Level 0.03

  38. Cosmic 0.45 External 0.26 Internal 0.27 Other <0.01 ~1.0 mSv/ year Natural Annual Dose Rates Estimated:

  39. Sources of Total Radiation Exposure in USA

  40. Annual Dose Rates – Health Care Medical X-rays 1.03 Dental X-rays 0.03 Nuclear Medicine 0.01 ~1.1 mSv/ year

  41. Maximum Permissible Doses • UBC Workers (members of public)1 mSv per year • Nuclear Energy Workers (NEWs )10 mSv per year (UBC)

  42. Engineer/Scientist Med Lab Tech

  43. Industrial Radiographer

  44. Dose Interval mSv 0 >0-1 >1-2 >2-5 >5-20 Annual Dose Rates 1997 Number of Workers 4198 516 25 6 2 Average Dose 0.00 0.32 1.48 3.37 6.2 X=0.05 mSv

  45. Canadian Exposures

  46. Acute Effects *2 Gy: cell depletion in bone marrow *2-5 Gy : cataracts *10 Gy: gastrointestinal syndrome *20 Gy: central nervous system Sv = Gy x QF (QF = 1 for gamma) SV~Gy (1 Gy = 100rads)

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