Radiation Exposure and Risk Assessment Maximum Permissible

Radiation Exposure and Risk Assessment

Maximum Permissible Dose General Public • • Whole Body 1 m. Sv/year Skin 50 m. Sv/year Hands Feet 50 m. Sv/year Lens of the eye 15 m. Sv/year

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

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

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

Radiation CANNOT be: • Felt So…how • Heardyou know do you have Tasted enough? • had • Smelled • Seen

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

Thermoluminescent Dosimeters Landauer Health Canada

Optically Read Dosimeters (Landauer)

Personal Alarm Dosimeter

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

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

External Exposure Estimate Where: • X = Dose (m. Sv) • = Specific Gamma Ray Constant • A = Activity (MBq) • t = Time (hours) • d = Distance from Source (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? • X = Total Dose • t = 44 hours • = 3. 24 (m. Sv*cm 2)/(h*MBq) at 1 cm • A = 185 MBq • d = 35 cm

X=Γ At (D)2 X = (3. 24) (m. Sv*cm 2)/(h*MBq) (185 MBq) (44 h) (35 cm)2 X = 21. 5 m. Sv

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

External Exposure Estimate • For gamma radiation

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

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

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 m. S per year…Will you buy it?

Section 3 - *B. E. I. R 7. Biological Effects of Ionizing Radiation *U. S. National Academy of Sciences Reports

“Radium Girls”

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

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

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

Somatic Effects and Risk Factors · 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

· 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

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

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

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

Dicentric chromosomes induced by radiation exposure Unexposed Exposed

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

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

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

Where does our radiation dose come from?

Natural Sources: Sky 100, 000 Cosmic Neutrons /hr 400, 000 Cosmic Gamma rays/hr Soil and Building 200, 000 Gamma rays/hr Air 30, 000 decays/hr Alpha, Beta, Gamma Food and Drink 15, 000 K- 40/hr 7, 000 Uranium/hr 12, 240, 000 C-14/hr

Dose Rates – Cosmic Rays Altitude μSv/hr 10 Km 5 6. 7 Km 1 Whistler 0. 1 Sea Level 0. 03

Natural Annual Dose Rates Estimated: • Cosmic • External 0. 45 0. 26 • Internal 0. 27 • Other <0. 01 ~1. 0 m. Sv/ year

Sources of Total Radiation Exposure in USA

Annual Dose Rates – Health Care Medical X-rays 1. 03 Dental X-rays 0. 03 Nuclear Medicine 0. 01 ~1. 1 m. Sv/ year

Maximum Permissible Doses n UBC Workers (members of public) 1 m. Sv per year n Nuclear Energy Workers (NEWs ) 10 m. Sv per year (UBC)

Engineer/Scientist Med Lab Tech

Industrial Radiographer

Annual Dose Rates 1997 Dose Interval m. Sv Number of Workers Average Dose 0 4198 0. 00 >0 -1 516 0. 32 >1 -2 25 1. 48 >2 -5 6 3. 37 2 6. 2 >5 -20 X=0. 05 m. Sv

Canadian Exposures

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 SV~Gy (1 Gy = 100 rads) (QF = 1 for gamma)

Attempted theft of Co-60 source 3 weeks 8 weeks

Industrial Radiography • Sealed radioactive sources: e. g. Iridium 192 • High activity: 58 curies = 2. 1 TBq

WARNING: Photo of gross anatomy Viewer discretion advised.

Other uses for sealed radioactive sources: -Internal calibration standards in liquid scintillation counters (Cs- 137) - Generation of ion current in electron capture devices e. g. gas chromatographs (Ni-63) *Inventory required for these instruments at UBC* -Industrial uses: volume measurement in closed vessels thickness measurement gauges food irradiation soil density gauges

Nuclear Gauges -Cs 137 : gamma source density gauges -Am 241/Be: neutron source moisture gauges -Portable: may require TDG training knowledge of regulations, documentation Expect occupational exposure -Safety through training: manual, courses offered by manufacturer

INCIDENCE OF CANCER BEIR VII – 2006 • Assuming an age/sex distribution similar to the entire US population: 42/100 people will be diagnosed with cancer = 42% §Acute exposure to 1. 0 m. Sv radiation (above background) could result in 1 new cancer per ten thousand = 0. 01% (LNT model) §Risk of cancer after acute exposure to 1. 0 m. Sv = 42. 01%

ALARA Principle As Low As Reasonably Achievable

Question? • Does radiation effect the human body through acute or chronic exposures? • Why do TB patients have a higher incident of breast cancer, but not lung cancer? – Different susceptibilities to damage from radiation • Do sealed sources of radiation have any risk associated with them? – Yes – can still offer significant damage