Radiation Overview
Dr. Halil Avci
Argonne National Laboratory
June 2010 | Argonne National Laboratory, USA
ENVIRONET Environmental Remediation Training Course
Outline
 Radiation Basics
 Sources of Radiation
– Naturally occurring
– Anthropogenic
 Site Contamination
– Contaminated media (soil, groundwater, surface water, buildings)
– Sources of contamination
 Radiation Dose and Risk
 Radiation Health Risk Assessment Overview
 Site Releases and Dose Standards
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Radiation Basics – The Atom and Radioactivity
• Stable Nuclei – low energy state
• Unstable Nuclei – high energy state
- Emits radiation
Electrons
Nucleus: Contains
protons and neutrons
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Radiation Basics – Radiation Types of Concern
Alpha Particles () -2 protons & 2 neutrons
Beta Particles () –
an electron (from the
nucleus)
Gamma Rays () -high-energy
electromagnetic
radiation
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Paper
Glass
Lead
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Radiation Basics – Measurement of Radiation
 Alpha, beta, and gamma radiation emitted by radioactive materials
can be measured directly using hand held or laboratory equipment.
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Radiation Basics – Activity and Half-Life
 Activity – rate of decay of a radioactive material
– Units: Curie (Ci) [3.7 × 1010 decays/s] and Becquerel (Bq) [1 decay/s]
 Half-life – amount of time required to reduce the amount of
radioactive material by 50%
Decay rate of radioactivity: After ten half-lives, the level of radiation is reduced to one thousandth
Time:
one
half-life
two
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three
four
five
six
seven
eight
nine
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Radiation Basics – Activity and Half-Life, continued

Activity = (Number of radioactive atoms) × 0.693/half-life
Note: for a given quantity of material, the longer the half-life, the less
radioactive is the material. Conversely, for a given radioactivity, the longer the
half-life, the greater is the quantity of the material.
Activity per
Unit Mass
(Specific
Activity)
Mass per Unit
Activity
Half-Life
Ci/g (Bq/g)
g/Ci (g/Bq)
Uranium-238
4.47 × 109 yr
3.36 × 10-7
(1.24 × 104)
2.97 × 106
(8.04 × 10-5)
Cesium-137
30.17 yr
86.6
(3.20 × 1012)
0.0115
(3.12 × 10-13)
8.04 d
1.24 × 105
(4.59 × 1015)
8.06 × 10-6
(2.18 × 10-16)
Radionuclide
Iodine-131
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Radiation Basics – Decay “Chains”
 Radioactive elements tend to decay
into other radioactive elements – decay
chains
 Decay chains end in a stable element
 Most decay chains are short
 Some decay chains are very long
 When successive members of a decay
chain have the same activity, they are
said to be in secular equilibrium
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Example – Uranium Decay Series
Uranium-238*
Uranium-234*

4.5 billion
 years
1.2 minutes
 240,000 years
Protactinium-234*

Thorium-230*
24 days
Thorium-234*
 77,000 years
Radium-226*
 1,600 years
Radon-222*
Polonium-214*
 3.8 days
NOTES:
Only the dominant decay mode
is shown.
The times shown are half-lives.
The symbols  and  indicate
alpha and beta decay.
An asterisk indicates that the
isotope is also a gamma
emitter.
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Polonium-210*


20 minutes
Polonium-218
Bismuth-214*
3.1
 minutes
5 days
160
 microseconds

 140 days

27 minutes
Lead-214*
Bismuth-210
22 years
Lead-210*
Lead-206 (stable)
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Sources of Radiation
 Natural Background (e.g., cosmic rays, radionuclides in soil and
geologic media, radon)
 Naturally Occurring Radioactive Material (NORM)
– Sometimes referred to as Technologically Enhanced Naturally
Occurring Radioactive Material (TENORM)
 Anthropogenic
– Weapons Programs(*)
– Nuclear Power(*)
– Radioisotope Applications(*)
• Medical
• Industrial
• Research
(*) Over the entire life-cycle of programs and applications
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Site Contamination
 Contaminated Media
–
–
–
–
Soil
Groundwater
Surface water
Building materials
• Surface contamination
• Volume contamination
 Sources of Contamination
–
–
–
–
Legacy waste disposal practices
Accidents
Normal operational releases
Abandoned facilities
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Radiation Dose
 Radiation deposits energy when it interacts with matter; the
amount deposited is called “dose.”
 Biological material (cells) can absorb energy from radiation,
leading to ionization, excitation, or cell damage.
 Depending on the type of radiation, the dose can be localized to
specific organs, or distributed across the whole body.
 Unlike radiation itself, dose cannot be measured directly. It is a
calculated quantity.
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Common Radiation Dose Terms
 Absorbed Dose (Rad or Gray): amount of energy deposited per
unit mass of material (The U.S. uses rad and the international
community uses Gray, 1 Gray = 100 rads)
 Dose Equivalent (Rem or Sievert): measures of the biological
effectiveness of the incident radiation (The U.S. uses rem and
the International community uses Sievert (Sv); 1 Sievert = 100
rems.)
– For gamma and beta radiation: 1 rad = 1 rem = 0.01 Sv
– For alpha radiation: 1 rad = 20 rems = 0.2 Sv
– 1 mrem = 0.001 rem; 1 mSv = 0.001 Sv
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*
(*) Ubiquitous background consists of inhalation of radon
and thoron (2.28 mSv), external space (0.33 mSv), ingestion
(0.29 mSv), and external terrestrial (0.21 mSv)
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What Health Effects Can Result from Radiation
Exposure?

Detrimental effects of ionizing radiation include:
–
–
–
–
Carcinogenesis (can cause cancer)
Mutagenesis (can cause mutations in cells)
Teratogenesis (can cause birth defects)
Acute toxicity (can kill you)

Large doses of radiation (600,000 to 1,000,000 mrem) can cause
severe health effects, including death.

At normal environmental and occupational levels, the most important
effect is the increase in the potential for developing a latent fatal
cancer. (Latent means the cancer manifests itself later in life, long
[often years] after the exposure to radiation occurs.)
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Radiation Health Effects

Health effects are fairly well characterized for high doses of most types
of radiation.

Health effects are estimated from people with high exposures:
– Atomic bomb survivors
– Uranium miners
– Medical treatments

Effects from low-level exposures are extrapolated from those seen at
high doses.
Bottom line: we know fairly well what happens at high doses;
we estimate what happens at low doses.
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Linear Extrapolation of Dose-Response Relationship
Where We
Have Data
Response
•
•
•
Doses We Are
Interested In
Dose
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Radiation Health Risk Assessment Overview
 Potential receptors and exposure scenarios
 Pathways analysis
 Dose estimates
 Risk estimates
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Environmental Pathways from a
Contaminated Site to Receptors
Source Release
Transport
air transport
Toxicity Data
Estimated
Risks
Exposures
inhalation
Intakes/Doses
deposition
incidental
ingestion
food
ingestion
dermal contact
surface water transport
biouptake
inhalation
dermal contact
incidental ingestion
drinking water ingestion
dermal contact
leaching to
groundwater
groundwater transport
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Radiation Health Risk Assessment Overview, continued
 Potential receptors and exposure scenarios
 Pathways analysis
– Concentrations of radionuclides at the point of receptors
 Dose estimates
 Risk estimates
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Exposure Routes for Radionuclides
Exposure point
concentration
• Gases
Inhalation
• Airborne dust
Ingestion
• Soil
• Water
• Food
• Soil
• Air
• Water
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External
Exposure
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Dose Estimates from Exposure-Point Concentrations
 For inhalation and ingestion
– Dose = Intake × Dose Conversion Factor (DCF)
– Intake = Amount of radionuclide inhaled or ingested (Ci or Bq)
• For inhalation:
Intake = (Concentration of radionuclide in air in Ci/ft3 or Bq/m3) ×
(breathing rate in ft3/s or m3/s) × (exposure duration in s)
• For ingestion:
Intake = (concentration of radionuclide in food or water in Ci/lb or
Bq/kg) × (consumption rate of water or food in lb/day or kg/day)
× (exposure duration in day)
– DCF is obtained from literature (e.g., ICRP 26/30 or the
U.S. Environmental Protection Agency’s Federal Guidance
Report (FGR) No. 11)
• Units are rem/Ci or Sv/Bq
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Dose Estimates from Exposure-Point Concentrations,
continued
 For external exposure
– Dose = Concentration × DCFe × exposure duration
– Concentration = Concentration of radionuclide in exposed media
•
•
•
•
Air: Ci/ft3 or Bq/m3
Water: Ci/ft3 or Bq/m3
Ground Surface: Ci/ft2 or Bq/m2
Soil: Ci/ft3 or Bq/m3
– DCFe is obtained from literature (e.g., ICRP 26/30 or FGR No.12)
in units of
•
•
•
•
Air: rem per Ci sec per ft3 or Sv per Bq s per m3
Water: rem per Ci sec per ft3 or Sv per Bq s per m3
Ground Surface: rem per Ci sec per ft2 or Sv per Bq s per m2
Soil: rem per Ci sec per ft3 or Sv per Bq s per m3
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Dose Estimates from Exposure-Point Concentrations,
continued
 DCFs can be organ-specific (e.g., lung, red bone marrow, bone
surfaces, thyroid, gonads, breast) or whole body.
 Doses are calculated for each radionuclide and each exposure
route (inhalation, ingestion, external).
 Total dose is the sum of doses from all radionuclides and
exposure routes.
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Dose Estimates from Exposure-Point Concentrations –
Example Calculations

Inhalation
–
–
–
–
–
–

Concentration of Radionuclide 1 in air = 105 Bq/m3
Breathing rate = 8,400 m3/yr = 2.7 × 10-3 m3/s
Exposure duration = 2 hr = 7,200 s
Intake = (106 Bq/m3) × (2.7 × 10-3 m3/s) × (7,200 s) = 1.9 × 106 Bq
DCF for inhalation = 1 × 10-10 Sv/Bq
Inhalation dose from Radionuclide 1 = (1.9 × 106 Bq ) × (1 × 10-10 Sv/Bq) = 1.9 × 10-4 Sv
Ingestion
–
–
–
–
–
–
Concentration of Radionuclide 2 in tomatoes = 103 Bq/kg
Consumption rate = 0.5 kg tomatoes/day
Exposure duration = 10 days
Intake = (103 Bq/kg ) × (0.5 kg/d)*10 d = 5 × 103 Bq
DCF for ingestion = 5 × 10-9 Sv/Bq
Ingestion dose from Radionuclide 2 = (5 × 103 Bq ) × (5 × 10-9 Sv/Bq ) = 2.5 × 10-5 Sv
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Dose Estimates from Exposure-Point Concentrations –
Example Calculations, continued

External Exposure
–
–
–
–

Concentration of Radionuclide 1 on ground surface = 106 Bq/m2
Exposure duration = 105 s
DCF = 1 × 10-17 Sv/Bq s per m2
Dose from external exposure to Radionuclide 1 = (106 Bq/m2 ) × (105 s ) ×
(1 × 10-17 Sv/Bq s m-2 ) = 10-6 Sv
Total Dose assuming the same individual is exposed to Radionuclide 1
through inhalation and external exposure and Radionuclide 2 through
ingestion
– Total Dose = 1.9 × 10-4 Sv + 2.5 × 10-5 Sv + 10-6 Sv = 2.16 × 10-4 Sv
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Radiation Health Risk Assessment Overview, continued
 Potential receptors and exposure scenarios
 Pathways analysis
– Concentrations of radionuclides at the point of receptors
 Dose estimates
 Risk estimates
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Radiation Health Risk Estimates

Radiation cancer health risks (in terms of mortality [death] and morbidity
[incidence]) can be calculated using radionuclide-specific risk coefficients
(also called slope factors) developed by the U.S. EPA (similar to the way
dose conversion factors are used to calculate dose).
– EPA’s risk coefficients are given in FGR No. 13. They are given in units of risk
per Bq inhaled or ingested (for internal exposures), and in units of risk per Bq-s
per m3 for submersion, Bq-s per m2 for ground surface, and Bq-s per kg for soil
contamination (external exposures).

Often the risk is calculated by applying a dose-to-risk conversion factor to
the total whole body dose.
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Radiation Health Risk Estimates, continued

Dose-to-risk conversion factors are developed by international organizations
(such as the United Nations Scientific Committee on the Effects of Atomic
Radiation [UNSCEAR] and the International Commission on Radiation
Protection [ICRP]) and adopted by national organizations.

Dose-to-risk coefficients used for workers are generally lower than the
coefficients used for the general public (e.g., ICRP Publication 60 gives
4 × 10-4 per person-rem [4 × 10-2 per person-Sv] for workers, and 5 × 10-4
per person-rem (5 × 10-2 per person-Sv] for general public for cancer
mortality).

There is a lot of uncertainty in risk coefficients and dose-to-risk conversion
factors.
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Radiation Health Risk Estimates – Example
Calculation

Assume
– Dose = 2.2 × 10-4 Sv
– Dose-to-Risk Conversion Factor for Cancer Mortality = 5 × 10-2 per
person-Sv
– Risk of Cancer Mortality = (2.2 × 10-4 Sv) × (5 × 10-2 /Sv) = 1 × 10-5
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Concepts of Clearance, Exclusion, and Exemption (Source:
ANSI/HPS N13.12-1999 and IAEA Safety Guide RS-G-1.7)

Clearance: Removal of items or materials that may contain residual levels
of radioactive materials within authorized practices from any further control
of any kind. Clearance implies that the subject materials or objects were
under regulatory control.

Exclusion: Designation by a regulatory authority that the magnitude or
likelihood of an exposure is essentially unamenable to control through
requirements of a standard and such exposures are outside the scope of
standards, e.g., exposure from 40K in the body, from cosmic radiation at the
surface of the earth and from unmodified concentrations of radionuclides in
most raw materials.

Exemption: Designation by a regulatory authority that specified uses of
radioactive materials or sources of radiation are not subject to regulatory
control because the radiation risks to individuals and the collective
radiological impact are sufficiently low.
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Standards and Generic Guidelines for Exemption of Radiumand Thorium-Contaminated Sites in the United States
 U.S. EPA standards for remediation of uranium mill tailings sites
(40 CFR 192.12):
– Remedial actions shall be conducted so as to provide reasonable
assurance that, as a result of residual radioactive materials from any
designated processing site:
(a) The concentration of radium-226 in land averaged over any area of 100
square meters shall not exceed the background level by more than—
1) 5 pCi/g (0.185 Bq/g), averaged over the first 15 cm of soil below the
surface, and
2) 15 pCi/g (0.555 Bq/g), averaged over 15-cm-thick layers of soil more
than 15 cm below the surface.
 U.S. Department of Energy (DOE) has generic guidelines for
remediation of radium- and thorium-contaminated sites (DOE Order
5400.5) that are similar to the EPA standards for uranium mill
tailings sites.
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Site Release Options
 Any use (no restrictions on the use of the property; cleared, exempt,
or excluded)
 Limited use (e.g., industrial, recreational – access to the site is not
controlled)
 Restricted use (access to the site is controlled)
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Site Release and Dose Standards

Site release is based on some primary dose criterion.

The primary dose criterion used by most nationalities and organizations is
100 mrem/yr (1 mSv/yr) from all practices (as recommended by ICRP
Publication 60).
– U.S. Nuclear Regulatory Commission uses 25 mrem/yr (0.25 mSv/yr) for license
termination
– U.S. EPA uses 10-4 to 10-6 risk for Superfund sites instead of dose

Radionuclide-specific activity concentrations are derived based on certain
future use of the site (e.g., residential, industrial, recreational, controlled
access) that correspond to the dose criterion.

The site is remediated to achieve the derived concentration levels.

The dose criterion used for exclusion and exemption is generally 1 mrem/yr
(10 micro Sv/yr). Screening level activity concentrations are developed for
exclusion or exemption (see for example ANSI/HPS N13.12-1999 and IAEA
Safety Guide RS-G-1.7).
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