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

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