Radiation Protection Basics

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Radiation Protection Basics
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Internal Dose
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• Routes of entry
– Inhalation
– Ingestion
– Percutaneous (skin absorption)
– Wounds (through openings in skin)
• Bioassay: measurement of radioisotope burden
– Products for sampling: urine, nail clippings, sweat,
exhaled air, hair, etc.
– In vivo: various whole body scanners
A snapshot
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• Radioisotope burden at time of measurement is
just that.
– Actual amount of radioactivity at time of uptake will
be greater
• Decay
• Excretion
• Chemical form of radioisotope is important
– Especially, whether soluble or insoluble
Fate of contaminants
• Insoluble
– If inhaled, trapped in mucus layer
– Eventually shuttled to GI tract
– Particle size, pulmonary rates important
– Pass through GI tract if ingested.
• Soluble
– Evenly dispersed through body fluid, or
– Seeks specific organ (testis, thyroid, colon)
– Seeks bone
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Kinetics of soluble contaminants
• Body fluids
– Filtered by kidneys
– Exponential decrease in concentration
• Organ uptake
– Rapidly cleared with sizeable portion take up by
organ
– Slower, long term release from organ
• Bone uptake
– Much slower turnover, long term deposition
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Uptake of commonly used radioisotopes
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• Note: levels of interest range from organ system
down to molecular
• Tritium (3H)
– Readily exchangeable element
– Absorbed through skin, enters total body fluid
– Limits on how much can be used before bioassay is
required; urine samples
•
14C
– Critical organ: fat tissue (high C concentration?)
– Entry depends on chemical form
continued
•
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32P, 33P
– 20% of ingested or inhaled soluble isotope taken up
by bone. Lungs and GI tract also affected,
depending on route of entry.
– Rapidly dividing cells incorporate isotope into
nucleic acids, long retention.
•
35S
– Entry depending on exposure
– Testis most at risk
continued
•
125I, 131I
– Sizeable amount absorbed by thyroid gland.
– Iodine isotopes are gamma emitters
– Work with Iodine usually requires monitoring by
thyroid scan.
•
51Cr
– Used in immunology research
– Excreted through GI tract, so accumulated and
concentrated there.
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Terms related to dose calculations
• Effective dose
– Like rem calculations, except in addition to the
radiation type getting a fudge factor, the target
organ gets one also.
– The rem x the organ sensitivity factor, all added to
get a whole body equivalent dose.
• Committed dose
– Dose received from an intake, calculated on the
basis of 50 years (70 for children or members of
public)
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Basic Tenets of Radiation Safety
• ALARA
– As Low As Reasonably Achievable
– Reflects uncertainty re dangers of low dose
radiation.
– All work to be carried out in ways that minimize
dose as much as possible without huge
inconvenience or expense.
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The 3 Guiding Principles
of Radiation protection
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• Shielding
– Know the radiation you are working with; choose a
barrier that is suitable.
• Lead for gammas, wax for neutrons; avoid lead
for high energy betas
• Time
– The less time you spend in a radiation field, the
lower your dose.
• Distance
– The inverse square rule: intensity = 1/r2 The farther
you are away, the lower your dose.
Rules reflect concerns
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• Danger: internal contamination
– Radioisotopes used in biological research seldom
irradiate much, so internal exposure bigger problem
– NO EATING, DRINKING, SMOKING or applying of
cosmetics. All actions that potentially produce
internal exposures.
• Loss of Control
– Careful record keeping
– Frequent swipe tests, surveys
– Locking of doors, challenging the unauthorized
Emergency actions
•
•
•
•
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1. health is first
2. cordon off area
3. maintain constant monitoring
4. contact RSO- he makes further decisions on
calling ADH, instructing on cleanup.
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Regulatory Issues
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• Society’s changing views and historical events
– Pre-1945: Drinks & baths in radium salts for health
– 1945: Boom; 1950’s mutants in the movies
– 1960’s: counterculture + industry arrogance +
earthquake zones in California, epicenter of
counterculture. “The Atom and the Fault”- good reading
– March 1979: Three Mile Island, Pennsylvania
– April 1986: Chernobyl, the Ukraine
– September 11, 2001: Terrorist attack on NYC
• Increasing fear, so increased regulatory
pressure
Who’s in charge?
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• Nuclear Regulatory Commission (NRC)
– Reports to Congress
– Oversees programs of “agreement states”
– Oversees nuclear power industry and governement
research facilities.
• Agreement states
– Make up their own rules, within NRC guidelines
– Administer their own programs
– 34 out of 50 currently
– Arkansas is an agreement state
Who’s in charge-2
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• Arkansas Department of Health (ADH)
– Not as reasonable as in the past
– The BIG YELLOW BOOK
• Rules and Regulations for Control of Sources of
Ionizing Radiation”
– Universities, hospitals, industries
– Issue a license to use and possess radioactive
materials
• On campus: the Radiation Safety Committee
The License
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• The license spells out our responsibilities as an
institution
– We spell out how we will meet the requirements
specified by ADH
– We get to write the license (within certain
guidelines), but we are held explicitly to it!
– Examples: how much radioactive material we will
have on hand, who gets to use it, how we will police
its use and check for contamination, etc.
Radiation Safety Manual
• Mostly for benefit of faculty and staff
– Shows ADH that we are in control of program
• Lists a variety of useful information
– Summary of state regulations
– License requirements
– Administrative structures
– General practices and requirements
• Online:
– http://ehc.astate.edu/Radiation.htm
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To use radioactivity on campus
• Provide proof of training
• Specific requests for isotope and amounts
• Clearly described experimental procedures
– So committee can evaluate safety
• Promise to be in compliance with all rules,
regulations, and procedures
– Includes records of receipt, use, disposal, wipe
tests.
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The biggest issue on campus:
Control of material
Safety obviously important, but
danger posed by isotopes used on
campus is minimal.
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