Radioactive Materials II

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Radioactive Materials II

• Radiation Protection

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Major Types of Ionizing Radiation Alpha, Beta,
Gamma
Alpha Particle Helium Nucleus that has a 2
charge
He 2
Large Mass (nuclei) Range 1-2 centimeters in air
Beta Particle electron that originates from
inside the nucleus
Small Mass (subatomic particle) Range 0-2 meters
in air
Gamma Photon and X-Rays
Electromagnetic Radiation No mass Range of
meters in air
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Ionizing Radiation interacts with matter and
produces a dose that is absorbed by that matter
a
He 2
ß
Gamma and xray
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RAD and REM

• Rad is an acronym that stands for Radiation
  Absorbed Dose. It is a measurement of the
  amount of energy deposited by any type of
  radiation in any material.
• It does not account for the interaction with
  biological molecules and potential for biological
  damage.
• Rem stands for Radiation Equivalent Man or
  Roentgen Equivalent Man

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RAD and REM

• Rem Rad x Q, where Q is a quality factor
  related to the probability of damage caused by
  the particular type of radiation.

• Q factors
• X or gamma ray -- 1
• Beta particles -- 1
• Neutrons (low E) -- 5
• Neutrons (hi E) 10
• Alpha particles 20

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Radiation Risk

• High Dose (acute)
• 100-400 rem effects blood cell counts, but
  people usually recover
• 400-1400 rem GI track, and epithelial cells
  effected. Lower end survive,. Upper end dont
• Above 1400 rem..death likely
• Atomic Bomb Victims
• Chernobyl nuclear meltdown

• Low Dose
• Risk related to chance of mutation
• Above 50 rem, risk proportional to dose
• Below 50 rem, risk assessment less clear.
• Effects below 10 rem unknown.
• Primary risk is induction of cancer

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Acute Radiation Syndromes(Very high radiation
doses)
Between 0 and 100 rads Generally there are no
clinically observable changes Some nausea at the
high end of range in more susceptible
persons Some blood changes above 25 rads
100 - 400 rads The hematopoietic system is
affected Blood cell precursors are very
radiosensitive Gradual depression in blood count
over days or weeks Increased susceptibility to
infection and hemorrhage Most recover at lower
end of range with some medical care
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Acute Radiation Syndromes(Continued)
400-1400 rads Gastrointestinal system is
affected Cells lining the intestinal track are
radiosensitive Bacteria and toxic material gain
entry into the bloodstream Diarrhea, dehydration,
infection, toxemia Survival is unlikely at the
upper end of range
Above 1400 rads Cardiovascular and Central
Nervous System is affected Blood supply is
impaired leading to nausea, vomiting,
convulsions, or unconsciousness. There is no
hope for survival
LD 50/30 is approximately 450 rads with modest
medical treatement
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High Dose Radiation?

• How likely?
• Chernobyl-like explosion..a catastrophe
• Approximately 100x the radioactivity released as
  combined Hiroshima/Nagasaki bombs
• 134 persons received over 70 rem exposure
• 28 deaths from Acute Radiation Sickness
• Atomic Blast
• Hiroshima
• 90-140,000 persons died within 4 months, but that
  includes all causes of death. Estimate that
  2-5000 of these died of Acute Radiation Sickness
  
• So even in the worst case scenarioacute
  radiation sickness is not the big worry

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What this means

• Very few deaths have ever been tied in a clear
  cut correlation to radiation. It can only be
  done with acute radiation exposure.
• Many, many more people were exposed to low level
  radiation from these incidents.
• 5.5 million people continue to live in areas
  contaminated by the Chernobyl incident
• Longest running studies are of Hiroshima/Nagasaki
  survivors Of 52,000 survivors who received 0.5
  rem doses, 420 deaths due to radiation exposure
  observed, out of a total of 8100 cancer deaths.

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Low-Dose Radiation Effects

• Non-stochastic
• Severity related to dose
• Cataracts
• Threshold dose

• Stochastic effects
• Random, delayed effects
• Possibility related to dose
• Severity not related to dose
• Mutation vs. no mutation

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Low Dose Radiation Injury

• At low doses, radiation injury is a statistical
  probability of interaction of the radioactive
  emission and biological molecules.
• Low dose radiation injury is primarily due to
  mutagenesis.
• Primary somatic biological effect caused by
  mutagenesis is cancer.
• Radiation damage to DNA in eggs or spermatocytes
  can lead to heritable mutations.

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What factors influence probability of radiation
damage?
Type of Target Cell
Law of Bergonie and Tribondeau
The radiosensitivity of a population of cells is
directly proportional to their mitotic rate and
inversely proportional to their degree of
differentiation.
In other words, the more frequently cells divide,
the more sensitive they are to radiation injury.
The more specialized the cells are, the less
sensitive they are to radiation injury.
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What factors influence probability of radiation
damage?

• Radiation Dose
• Type
• Activity (how much)
• Time of exposure

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DOSE LIMITS
If risk of injury is stochastic, how do we know
how much radiation is required to increase the
risk? As with any statistical, stochasitic
process, you cant know for sure. Models are
developed. Most are very conservative. This
primary risk models have been developed by the
National Academy of Sciences, the National
Council on Radiation Protection and others.
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Models for risk estimation
New evidence from National Academies of Science
BIER VII, 2005 suggests that the Linear No
Threshold model is supported.
Range of estimated effects at low dose
Range of known effects at high dose
Additional cancer risk due to radiation
1 Linear model 2 Linear Quadratic model 3
Threshold dose effect model 4 Increased effect
at low dose
100
0
Dose (REM)
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DOSE LIMITS
Whats my risk of getting cancer from a radiation
exposure? This is hard to determine. The most
quoted estimate is that an exposure of 10000
workers to 1 rem of radiation would produce 4
cancers 0.04. Consider that in the US as a
whole the risk of cancer is about 25
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Regulatory Premises

• Competing and mostly unsupported models for risk
  require using a conservative approach
• LNT (linear, no threshold) assumes any dose is
  harmful.
• ALARA (as low as reasonably acheivable)
• Do better than the regulatory limits on dose
• Provides a margin of safety

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Regulatory limits

• Nuclear Regulatory Commission
• Sets the dose limits
• Radiological workers
• Members of the Public
• Neither limit is zero.
• States and other agencies may set more stringent
  limits
• All expect ALARA

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What are the regulatory limits?

• Members of the Public
• 100 mRem in year
• 2 mRem in one hour

• Radiological Workers
• 5 Rem in one year
• 50 Rem to one organ or tissue
• 15 Rem to eye
• 50 Rem to skin or extremity
• These are referred to as occupation dose limits.

Why are these limits different? Are members of
the public less sensitive to Radiation?
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Types of exposure
External Exposure High energy Betas Gammas
Internal exposure requires intake of
radioisotope Alpha, Beta and Gamma
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• External Exposure Reduction
• Time
• reduce time spent in radiation area
• Distance
• stay as far away from the radiation source as
  possible
• Shielding
• interpose appropriate materials between the
  source and the body

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Reducing Exposure Time

• Training
• Rehearsal of procedures prior to using
  radionuclide.
• Improves efficiency, reduces handling time.
• Equipment
• Shakers rather than hands!
• Lab/Workplace design
• Easy access to the equipment and components
• Task modifications from ALARA review

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Controlling Distance

• Remote operation
• manipulating devices forceps not fingers!
• Move away from sources
• remain near a source only when it is being used
• Removal of other radiation sources
• waste containers
• unnecessary sources

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Shielding

• Basic principle Place materials between the
  source and person to absorb some or all of the
  radiation
• a radiation no shield required for external
  exposures dead skin layer stops ?s
• b radiation ranges of meters in air some can
  penetrate dead skin layer thin plexiglass
  shields adequate
• Low Z shielding reduces Bremsstrahlung
• X and ? radiation highly penetrating, best
  shields are high atomic number materials (lead)

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INTERNAL RADIATION EXPOSURE

• Entry paths
• Dust inhalation, fume or mist inhalation
• Ingestion of contamination
• Food, water, or from contaminated hands
• Injection (puncture wounds, accidental hypdermic
  needle injection, broken pipets, etc)
• Absorption through skin

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INTERNAL RADIATION EXPOSURE

• Rarely any method to reduce exposure once in the
  body
• Length of exposure depends on the physical and
  biological half-life
• Dose estimates are very difficult
• Usually dont know the amount of intake
• Biological variability in elimination from and
  concentration in tissues and in energy
  deposition.

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Controlling Internal Exposure

• PREVENT INTAKE!
• Safe Handling Practices!
• Contamination Control
• removable surface contamination
• airborne contamination
• Standard Procedures help!
• Personal
• No eating, drinking, smoking, make-up
  application, etc when working with RAM
• Procedures
• Work in hood
• Wear PPE
• Clean up contamination
• Survey to make sure no contamination exists
• Monitor Air, to make sure procedure doesnt
  release dust or volatiles

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Exposures in perspective

• You are exposed to ionizing radiation all the
  time. This is called background radiation.

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Exposures in perspective
Estimate your annual exposure
http//www.umich.edu/radinfo/ Walts Annual
non-occupational exposure 393 mREM. This is
pretty typical of the average American. Remember
the dose limit for an individual of the public
from our activities is 100 mREM. Is there a
scientific basis for this limit? NO.
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Comparative Risk Estimates
For fatal cancer induction, whole-body
irradiation 0.0005/rem/person Compare to
non-radiation cancer fatality risk (U.S.A.)
0.223/person/lifetime
For hereditary effects expressed in the first two
generations 0.0001/rem/person Compare to
single generation non-radiation risk
0.09/person
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BUT!

• The public perception of radiation risk is that
  it is always DEADLY RADIATION!
• This graphic shows how the media place stories on
  radiation out of proportion to risk. nb. There
  were NO documented deaths due to radiation in the
  time shown here.

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So, many of the issues related to management of
radioactive waste are related to public
perception as much as good science.
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Some Risk ComparisonsOne-in-a million chances of
dying
Situation
Cause of death 2.0 mrem
cancer from radiation travelling 700 miles by
air accident crossing the ocean by
air cancer from cosmic
rays traveling 60 miles by car
accident living in Denver for 2 months cancer
from cosmic rays living in a stone building for
2 months cancer from radioactivity working
in a factory for 1.5 wk accident working in a
coal mine for 3 hr accident smoking 1-3
cigarettes cancer heart-lung
disease rock-climbing for 1.5 minutes accident 20
min being a man aged 60 mortality from all
causes living in New York City for 3 days lung
cancer from air pollution
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Health Physics Society Recommends

• Estimates of risk should be limited to
  individuals receiving a dose of at least 5 rem in
  one year or a lifetime dose of at least 10 rem in
  addition to natural background.
• Below these doses, individual risk estimates
  should not be used expression of risk should be
  qualitative emphasizing the inability to detect
  any increased health detriment (i.e., zero health
  effects is the most likely outcome).
• For a population in which all individuals receive
  lifetime doses of less than 10 rem above
  background, collective dose is a highly
  speculative and uncertain measure of risk and
  should not be quantified for purposes of
  estimating population health effects