Radiation Exposure and Risk Assessment
Feb 02, 2016
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
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
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)
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
Radiation CANNOT be:
• Felt• Heard• Tasted• 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
5mSv/year (CNSC) 1mSv/year – UBC action level
How do I estimate my dose?Will I need to be monitored?
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
• 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?
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
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.
External Exposure Estimate
dAt
X 2
• For gamma radiation
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)
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 mS 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”
• 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
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
• 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
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
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 TypesDifferent Cell Cycle
Different Cell Targets
End Effect of Radiation
Organelle deathCell deathCell healingChromosome lossGene lossGene rearrangement
DNA Damage
Single Strand BreakDouble Strand Break*Change or Loss of Base
Bond Breakage- Uncoiling
Intra-Helix CrosslinkingInter-Helix CrosslinkingInter-Protein Crosslinking
Dicentric chromosomes induced by radiation exposure
Unexposed Exposed
In
cide
nce
of e
ffect
s
Increasing Radiation Dose
Atomic bomb victims*
*Chernobyl
LNT model: linear, no threshold
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
Atomic bomb victims*
Increasing Radiation Dose
Inci
denc
e of
eff
ects
*Chernobyl
“Normal Exposure”?
Radiation Hormesis
Threshold model
Where does our radiation dose come from?
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:
Dose Rates – Cosmic Rays
Altitude μSv/hr
10 Km 5
6.7 Km 1
Whistler 0.1
Sea Level 0.03
• Cosmic 0.45
• External 0.26
• Internal 0.27
• Other <0.01
~1.0 mSv/ year
Natural Annual Dose RatesEstimated:
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 mSv/ year
Maximum Permissible Doses
UBC Workers (members of public)
1 mSv per year
Nuclear Energy Workers (NEWs )
10 mSv per year(UBC)
Engineer/Scientist
Med Lab Tech
Industrial Radiographer
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
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 (QF = 1 for gamma)SV~Gy(1 Gy = 100rads)
3 weeks
Attempted theft of Co-60 source
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.
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
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%
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