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RADIATION PROTECTION PRINCIPLESINTERPRETING MEASUREMENTS & EVALUATION
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Dose limitsRadiation detectionDose measurement and monitoringALARA principlesReasons for doing surveysSurvey documentationThe importance of “zero”Case studies
Radiation dose limitsWhat are the basis for limits?Who establishes limits?TerminologyRadiation dose limitsMortality risk for the limits
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Basis for federal regulatory limitsICRP, IAEA and NCRP recommendations (since 1928)U.S. National Academy of Sciences Committee on Biological
Effects of Atomic Radiation (BEAR I)/Genetics Panel in 1956: Linear Non-threshold model should be used to establish limits
The Federal Radiation Council guidelines issued in 1960EPA issued its guidance on occupational exposure limits in 1994
and promoted the ALARA principleOSHA, NRC, DOE and DOD have statutory authority for workers
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Protection & RegulationNuclear Regulatory Commission (NRC)
Environmental Protection Agency (EPA)
Department of Homeland Security (DHS)
Radioactive Materials
Radiation Machines
Environmental Protection
Nuclear Security
Food & Drug Administration (FDA)
Agreement States
Department of Transportation (DOT)Transport
StatesManufacture Use
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TerminologyEffective dose equivalentCommitted effective dose equivalentsDerived air concentration (DAC)Annual limit on intake (ALI)
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Effective dose equivalentThe sum of the products of the dose equivalent to the organ or
tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated.
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Committed dose equivalent The dose equivalent to organs or tissues of reference that will be
received from an intake of radioactive material by an individual during the 50-year period following the intake.
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Committed effective dose equivalent The sum of the products of the weighting factors applicable to
each of the body organs or tissues that are irradiated and the committed dose equivalent to these organs or tissues.
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Derived air concentration (DAC)The concentration of a given radionuclide in air which, if
breathed by the reference man for a working year of 2,000 hours under conditions of light work (inhalation rate 1.2 cubic meters of air per hour), results in an intake of one ALI.
Annual limit on intake (ALI): The derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year.
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Internal dose must be calculated• Can be based on air sampling results• Whole body counting detects residual radioactivity for gamma
emitters (e.g. Co-60, Cs-137)• Bioassay is used for beta and alpha emitters (e.g. H-3, P-32, Sr-
90, Pu-238)• Assignment of dose is calculated using models published by the
International Council on Radiation Protection• ALIs tables in the regulations are derived from the models
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Radiation Dose Limits (10CFR20)Annual Limit
Total effective dose equivalent (total body) 5 rem (0.05 Sv)
Skin and individual tissues (except the lens) 50 rem (0.5 Sv)
Lens of the eye 15 rem (0.15 Sv)
Embryo/fetus* (for the duration of the pregnancy) 0.500 rem (5e-3 Sv)
Minors 0.500 rem (5e-3 Sv)
General public 0.100 rem (1e-3 Sv)
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*Declared pregnancy
What is the mortality risk for the limits?ICRP No. 26 "...the mortality risk factor for radiation-induced cancers is
about 10-4 per rem, as an average for both sexes and all ages... ." The risks of average occupational exposures (about 0.5 rem/year) are
roughly comparable to risks experienced in safe industries, 10-4 annually. At the permissible limit of 5 rem/year, the risk is comparable with that
experienced by some workers in occupations having higher-than-average risk.
For members of the public, the ICRP considered that an annual risk in the range of 10-6 to 10-5 would likely be acceptable (ICR77). The ICRP recommended an annual individual dose limit of 100 mrem (1 mSv) from all radiation sources.
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What is the ALARA principle?ALARA is an acronym used in radiation safety for “As Low As
Reasonably Achievable.” The ALARA radiation safety principle is based on the minimization of radiation doses and limiting the release of radioactive materials into the environment by employing all “reasonable methods.”
ALARA is a sound radiation protection principle and it is a regulatory requirement for all radiation protection programs.
3 Principal Means to Reduce External Exposure
Time - reducing the amount of time around a radiation source directly reduces radiation exposure.
Distance - exposure reduces exponentially with increased distance from the source.
Shielding - stops alpha and beta particles and greatly reduces x-ray and gamma radiation.
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Follows 1/r2
relationship
For example; doubling your distance cuts exposure to 1/4, and tripling distance cuts exposure to 1/9.
Increase Distance
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Shielding components on TMI-2 Reactor Building El. 305’
Methods to reduce radiation exposure• Use engineering controls if possible (e.g.
shielding, ventilation)• Maintain knowledge and awareness of
hazards• Maintain area control: signage, records, and
security• Design appropriate facilities and equipment
for use and control of radioactive materials
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Methods to reduce internal intake• Containment and/or exhaust (e.g., fume
hoods in labs)• Contamination surveys• Good hygiene - washing hands,
contaminated skin, and contaminated articles
• Good personal habits – no hand to face/mouth contact, no eating/drinking, no application of cosmetics
• Use of protective clothing and personal protective equipment
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Additional methods to reduce radiation exposure• Use good work planning and control• Maintain training and qualifications• Walk down the job using the procedure• Create mockups for high dose work• Ask questions and listen to the answers (i.e. consider all points
of view)
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Radiological Controls• Provide hazard communication to workers and public• Establish posting notification to restrict access and control
dose• Contain and maintain control of radioactive material• Control release of radioactive effluents to the environment• Provide real time monitoring of radiological conditions
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Posting requirements• Radiation area: > 0.005 rem (0.05 mSv) in 1 hour• High radiation area: >0.1 rem (1 mSv) in 1 hour• Airborne contamination area: > 1 DAC • Contamination area: control of loose surface contamination• Radioactive material storage area: storage and control of
radioactive material
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Radiation detectionPrinciples of radiation detectionTypes and uses of radiation detectors
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Dose measurement and monitoring
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Main methods of radiation detection instrumentsIonization of a gas and
collection of charged particles
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Geiger Mueller detector
G/M probe is good for detecting gamma at levels needed to establish radiation area posting
“Pancake” probe is good for detecting beta/gamma contamination
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Photoluminescent detectors
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Luminescence of a solid or a liquid and amplification of the signal through a photomultiplier tube
ZnS scintillator detector
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High efficiency for detecting alpha
Very thin mylar window keeps light out but allows alpha to pass through
Luminescent personal dosimeters
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Personal dosimeter
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• Provides real time monitoring of individual radiation dose
• Digital dosimeters can set alarms for dose rate and total dose
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Instrument Types Detection Principle ApplicationsIon chamber (IC) Ionization of air
(or other gases)Direct measurement of exposure or exposure rates, with minimal energy dependence.
Geiger-Mueller (GM)Proportional counter (PC)
Ionization of gas withmultiplication ofelectrons in detector
Detection of individual events, i.e. alpha or beta particles & secondary electrons, for measuring activity (in samples or on surfaces) & detecting low intensities of ambient x or gamma radiation; precautions required due to energy dependence.
Solid state diodes Ionization ofsemiconductor
Detection & energy measurement of photons or particles; primarilyfor laboratory use.
Solid state diodes Ionization & excitationfollowed by light emission
Detection of individual events
Solids NaI (Tl) - photons; energy spectrometryZnS (Ag) - alpha particles; detection only
Liquid Detection of low-energy beta emitters mixed with the scintillation fluid.
Luminescent dosimeter
Excitation of crystal;light release by heating or light
Personal and environmental exposure monitoring.
Why we measure anything
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Processes,Conditions,Behaviors
Reasons for doing surveys/monitoring
• Compliance with requirements (posting, controls, levels)
• Verifying what should be there• Looking for something that shouldn’t be there• Looking for changes
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How to interpret measurements
Do the survey/monitoring results:• Reflect anticipated conditions?• Reveal unexpected/expected changes in
conditions?• Seem unusually high/low?
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Places you might see contamination Broken or leaking containersWhen opening, pouring, or dispensing Spills or airborne releases Inadequate clean up
Regulatory requirements for surveysWAC 246-221-110 “Surveys” – says you have to do them
WAC 246-221-230 “Records important to radiation safety” – tells you how to document them
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Survey documentationEstablishes legal proof of complianceEnables verification of radiological conditionsEnables trending to provide early detection of adverse conditionsProvides effective hazard communication to workers
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Why a measured “zero” is so important
A documented “zero” provides incontrovertible, legal proof of a verified physical measurement
Some companies try to save money on dosimetry if they can demonstrate individuals are below 100 mrem/yr by surveys and area monitoring.
If individuals are working inside a “restricted area” they should have personal dosimetry
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Case studies1. Contaminated shoes in nuclear repair facility2. Internal dose mystery at Three Mile Island3. Elevated radiation levels near Brookhaven National Lab4. Fukushima scare in Half Moon Bay, CA5. Radioactive waste from a screw factory
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More Health Physics fun• Cascade Chapter of the Health Physics Society
May 4, 2018 (follow us on Facebook!)• Joint ANS/HPS topical symposium Tri-Cities
Sept 30 – Oct 3, 2018http://www.lowdoserad.org
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