Title: Radiation Exposure and
1Radiation 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
3Nuclear 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.
4Maximum Permissible Dose
Nuclear Energy Worker
- Whole Body 50 mSv/year
- Skin 500 mSv/year
- Hands Feet 500 mSv/year
- Lens of the eye 150 mSv/year
(CNSC)
5Radiation 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
Inform, Review, Reassign, Restrict
6Radiation CANNOT be
- Felt
- Heard
- Tasted
- Smelled
- Seen
Sohow do you know you have had enough?
7Dosimetry
- 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
8Thermoluminescent Dosimeters
Landauer
Health Canada
9Optically Read Dosimeters (Landauer)
10Personal Alarm Dosimeter
11Who 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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14How do I estimate my dose?Will I need to be
monitored?
15External Exposure Estimate
- Where
- X Dose (mSv)
- ? Specific Gamma Ray Constant
- A Activity (MBq)
- t Time (hours)
- d Distance from Source (cm)
16What 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 (mSvcm2)/(hMBq) at 1 cm
- A 185 MBq
- d 35 cm
17X G A t (D)2
X (3.24) (mSvcm2)/(hMBq) (185 MBq) (44h)
(35cm)2
X 21.5 mSv
18Who 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.
19External Exposure Estimate
20ESTIMATION OF EXTERNAL ß-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)
21Internal 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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23Question?
- 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 yearWill you
buy it?
24Section 3 - B.E.I.R
- Biological Effects of Ionizing
- Radiation
U.S. National Academy of Sciences Reports
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26Radium Girls
27B.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
28Effects 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
29Effects 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
30- 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
31- 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
3230 100 Trillion Cells at Risk
Different Cell Types Different Cell Cycle
Different Cell Targets
33End Effect of Radiation
Organelle death Cell death Cell
healing Chromosome loss Gene loss Gene
rearrangement
34DNA Damage
Single Strand Break Double Strand Break Change
or Loss of Base
Bond Breakage- Uncoiling
Intra-Helix Crosslinking Inter-Helix
Crosslinking Inter-Protein Crosslinking
35Dicentric chromosomes induced by radiation
exposure
Unexposed
Exposed
36LNT model linear, no threshold
Incidence of effects
37Incidence of Radium-Induced Malignant
Tumors
38Atomic bomb victims
Threshold model
Chernobyl
Normal Exposure?
Incidence of effects
Radiation Hormesis
Increasing Radiation Dose
39Where does our radiation dose come from?
40Natural Sources
41 Dose Rates Cosmic Rays
Altitude µSv/hr 10 Km 5 6.7 Km 1
Whistler 0.1 Sea Level 0.03
42Natural Annual Dose Rates Estimated
- Cosmic 0.45
- External 0.26
- Internal 0.27
- Other lt0.01
- 1.0 mSv/ year
43Sources of Total Radiation Exposure in USA
44Annual Dose Rates Health Care
Medical X-rays 1.03 Dental X-rays 0.03 Nuclear
Medicine 0.01 1.1 mSv/ year
45Maximum Permissible Doses
- UBC Workers (members of public) 1 mSv
per year - Nuclear Energy Workers (NEWs ) 10 mSv
per year
(UBC)
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47Industrial Radiographer
48Annual Dose Rates 1997
- Dose Interval
- mSv
- 0
- gt0-1
- gt1-2
- gt2-5
- gt5-20
Number of Workers 4198 516 25 6 2
Average Dose 0.00 0.32 1.48 3.37 6.2
X0.05 mSv
49Canadian Exposures
50Acute 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) SVGy (1 Gy
100rads)
51Attempted theft of Co-60 source
3 weeks
8 weeks
52Industrial Radiography
- Sealed radioactive sources e.g. Iridium 192
- High activity 58 curies 2.1 TBq
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54WARNING Photo of gross anatomy Viewer
discretion advised.
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56- 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
57- Nuclear Gauges
- Cs 137 gamma source
- density gauges
- Am241/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
58INCIDENCE 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 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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60 ALARA Principle As Low As
Reasonably Achievable
61Question?
- 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