Radiation Exposure and Risk Assessment
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Transcript of Radiation Exposure and Risk Assessment
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Radiation Exposure and Risk Assessment
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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
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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.
Nuclear Energy Workers
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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)
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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
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Radiation CANNOT be:
• Felt• Heard• Tasted• Smelled• Seen
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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
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Thermoluminescent Dosimeters
Landauer
Health Canada
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Optically Read Dosimeters
(Landauer)
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Personal Alarm Dosimeter
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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
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How do I estimate my dose?Will I need to be monitored?
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External Exposure Estimate
Where:
• X = Dose (mSv)
• = Specific Gamma Ray Constant
• A = Activity (MBq)
• t = Time (hours)
• d = Distance from Source (cm)
dAt
X 2
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• 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?
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X = (3.24) (mSv*cm2)/(h*MBq) (185 MBq) (44h) (35cm)2
X = 21.5 mSvX = 21.5 mSv
X = Γ A t (D)2
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Who SHOULD NOT wear a TLD?
A NEW who has only a
REMOTE POSSIBILITY of receiving a
radiation exposure greater than 1mSv/yr.
Personnel working with low energy betas
such as S-35, C-14 and H-3.
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External Exposure Estimate
dAt
X 2
• For gamma radiation
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ESTIMATION OF EXTERNAL β-RADIATION DOSENOT IN CONTACT WITH SKIN
•Rule of thumb, valid over a wide range of beta energies
2
2
27d
A
hrBq
mSvD
Dose Rate (Sv/hr)
Activity (Bq)
Distance from source (m)
•Assumes point source and no attenuation to air or source material
•Expect large errors beyond 1 m (overestimates absorbed dose)
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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
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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?
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Section 3 - *B.E.I.R
7. Biological Effects of Ionizing Radiation
*U.S. National Academy of Sciences Reports
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“Radium Girls”
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• 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
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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
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• 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
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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
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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
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30 – 100 Trillion Cells at Risk
Different Cell TypesDifferent Cell Cycle
Different Cell Targets
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End Effect of Radiation
Organelle deathCell deathCell healingChromosome lossGene lossGene rearrangement
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DNA Damage
Single Strand BreakDouble Strand Break*Change or Loss of Base
Bond Breakage- Uncoiling
Intra-Helix CrosslinkingInter-Helix CrosslinkingInter-Protein Crosslinking
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Dicentric chromosomes induced by radiation exposure
Unexposed Exposed
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In
cide
nce
of e
ffect
s
Increasing Radiation Dose
Atomic bomb victims*
*Chernobyl
LNT model: linear, no threshold
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Incidence of Radium-Induced Malignant Tumors
0
0.2
0.4
0.6
0.8
1
3.7 kBq 37 kBq 370kBq 3.7 MBq
Inci
den
ce
Estimated Maximum Radium Burden in Bq
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Atomic bomb victims*
Increasing Radiation Dose
Inci
denc
e of
eff
ects
*Chernobyl
“Normal Exposure”?
Radiation Hormesis
Threshold model
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Where does our radiation dose come from?
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Sky 100,000 Cosmic Neutrons /hr400,000 Cosmic Gamma rays/hr
Air 30,000 decays/hrAlpha, Beta, Gamma
Food and Drink15,000,000 K- 40/hr7,000 Uranium/hr
12,240,000 C-14/hr
Soil and Building200,000,000 Gamma rays/hr
Natural Sources:
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Dose Rates – Cosmic Rays
Altitude μSv/hr
10 Km 5
6.7 Km 1
Whistler 0.1
Sea Level 0.03
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• Cosmic 0.45
• External 0.26
• Internal 0.27
• Other <0.01
~1.0 mSv/ year
Natural Annual Dose RatesEstimated:
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Sources of Total Radiation Exposure in USA
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Annual Dose Rates – Health Care
Medical X-rays 1.03
Dental X-rays 0.03
Nuclear Medicine 0.01
~1.1 mSv/ year
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Maximum Permissible Doses
UBC Workers (members of public)
1 mSv per year
Nuclear Energy Workers (NEWs )
10 mSv per year(UBC)
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Engineer/Scientist
Med Lab Tech
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Industrial Radiographer
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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
6.2X=0.05 mSv
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Canadian Exposures
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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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3 weeks
Attempted theft of Co-60 source
8 weeks
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Industrial Radiography•Sealed radioactive sources: e.g. Iridium 192•High activity: 58 curies = 2.1 TBq
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WARNING: Photo of gross anatomy
Viewer discretion advised.
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Nuclear Gauges
-Cs 137 : gamma sourcedensity gauges
-Am241/Be: neutron source moisture gauges
-Portable: may require TDG trainingknowledge of regulations, documentation
Expect occupational exposure
-Safety through training: manual,courses offered by manufacturer
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INCIDENCE OF CANCERBEIR 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 mSv radiation (above background) could result in 1 new cancer per ten thousand = 0.01% (LNT model)
Risk of cancer after acute exposure to 1.0mSv = 42.01%
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ALARA Principle
As Low As Reasonably Achievable
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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