Radon Level Assessment

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Radon Level Assessment

• Denis Rubin
• BME 519

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What is Radon?

• Radon (222Rn) is 86th element of periodic table
• Discovered in 1900 by German chemist Friedrich E.
  Dorn
• Chemically inert, uncharged noble gas
• Odorless, tasteless and invisible
• Produced from uranium-238 decay chain
• Decay product of radium-226
• Half-life 3.8 days
• Decays by alpha particle emission
• a-particle energy 5.48 MeV
• No beta or gamma emissions
• Produces short-lived solid alpha-emitters
• Polonium 218 and 214
• Produces short-lived solid beta-emitters
• Lead 214
• Bismuth 210 and 214
• Polonium 210 and 214

http//www.atral.com/U2381.html
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Where is Radon Found?

• Product of Uranium
• Ubiquitous
• Seeps out of rocks and soil
• Heavy gas builds up indoors (basements, etc.)
  and in mines
• Outdoor radon does not constitute a health risk
  due to its low concentration
• Can dissolve in water
• Low 222Rn levels in rivers, ponds, seas, etc.
• High levels of radon can be found in well water
• Can be present in water obtained from underground
• Average radon level in homes is about 1.25 pCi/L

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Rates of Developing Lung Cancer
Among Men by State
Rates of Developing Lung Cancer
Among Women by State
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Risk Assessment

• Annual lung cancer deaths from radon is about
  21,000
• (with an uncertainty range of 8,000 to 45,000)
• Leading cause of lung cancer among non-smokers
• 2nd leading cause of lung cancer among smokers
• Biggest contributor to natural background
  radiation level
• 200 out of 300 mrem/yr come from exposure to 222Rn

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 748.
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Three Types of Radon Level Measurement

• Grab sampling
• Instantaneous measurements of the radon or radon
  progeny concentration in air over time intervals
  that are short (on the order of minutes) compared
  to the time scale of fluctuations in
  concentration.
• The air is collected in a container and brought
  back to the laboratory for analysis. Typical
  containers include plastic bags, metal cans and
  glass containers.
• The volumes of the containers are usually between
  5 liters and 20 liters.
• Continuous sampling
• Continuous sampling involves the automatic taking
  of measurements at closely spaced time intervals
  over a long period of time. The result is a
  series of measurements which can give information
  on the pattern with which the concentration
  varied throughout the measurement interval.
• Integrating Sampling
• Integrating devices collect information on the
  total number of radition events which occur
  throughout some fairly long period of time,
  usually on the order of several days to months.
  The result from integrating devices is an
  estimate of the approximate average concentration
  through the environment interval.

http//enhs.umn.edu/hazards/hazardssite/radon/rado
nmeasure.html
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Measurement of Radon in Air

• Alpha-particle scintillation counting with ZnS
  (Lucas Cell)
• Uses grab sample
• The radon gas sample is introduced into a
  counting cell.
• The inside wall of the cell is coasted with zinc
  sulfide (ZnS), except one end which is covered
  with a transparent window for coupling to a PMT.
• When ?-particle strikes the wall of the cell, a
  flash of light is emitted from the ZnS coating.
  The light is detected by the PMT and translated
  into an electrical signal.
• The efficiency of these cells is typically 70 to
  80.
• Background rates are low, about 0.1 or 0.2 counts
  per minute (cpm).
• Internal ionization chamber counters
• ?-particles and daughters of radon can also be
  detected in ionization chambers.
• Used either to count electrical pulses from
  individual decay events or to measure currents
  resulting from the integrated effect of all
  decays.
• Not as popular as Lucas cells more expensive and
  show no major advantages.
• Two-filter methods
• For measurement of both radon and radon daughter
  concentrations
• Air is passed through the first filter where
  daughter products are removed.
• Air is passed through a long decay chamber, where
  daughter products are allowed to grow in and are
  collected on a second filter.
• Filters counted separately to determine the
  concentration of
• radon (from the second filter)
• daughter products (from the first filter).
• The above methods are used for measurement of
  both grab samples and continuous samples.

http//enhs.umn.edu/hazards/hazardssite/radon/rado
nmeasure.html
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Measurement of Radon Daughter in Air

• Radon daughters are solid
• Deposit on dust particles and other surfaces.
• Draw air through a filter and collect radon
  daughters with high efficiency
• Daughters have short half-lives (longest 27min)
  count quickly
• Need to know individual daughter concentrations
• Po-218, Pb-214, and Bi-214. (Po-214 not relevant
  extremely short half-life)
• Count the alpha-particle radioactivity deposited
  on the filter, using a scintillation counter with
  a ZnS phosphor.
• Determine the three radon daughter
  concentrations
• Because the half-lives of the three daughter
  nuclei are different, the relative number of
  counts in three time period determines their
  individual initial concentrations.
• Differentiate daughters based on their energies
  (?-particle spectroscopy)
• 6.00-MeV alpha-particle group from Po-218
• 7.69-MeV alpha-particle group from Bi-214
• Count the two groups separately during two time
  periods.
• Combined alpha-particle and beta-particle
  spectroscopy
• The counting of beta-particles from Pb-214 and
  Bi-214 in a plastic scintillator along with
  ?-particle spectroscopy with a surface-barrier
  detector determines the three daughter
  concentrations during a single time period.
• This method is clearly advantageous in terms of
  speed of measurement, but more complex in terms
  of the equipment required.

http//enhs.umn.edu/hazards/hazardssite/radon/rado
nmeasure.html
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Radon measurement in water

• Liquid scintillation counters
• When the radon concentration in water is
  sufficient high (gt 1000 pCi/L), the water sample
  can be mixed with the counting material and
  counted by the conventional liquid scintillation
  counters used for radon in air samples.
• Gas extraction
• For lower concentrations, extract radon as a gas
  and count the emitted alpha particles in a ZnS
  scintillation cell. Helium is bubbled through the
  water, striping the radon. The mixture of gases
  is then passed through a cold trap, for example
  activated charcoal at liquid nitrogen
  temperature, that traps radon while the helium
  passes through. The trap is then warmed and radon
  is transferred into a Lucas counting cell by
  stripping with a small amount of helium.
• Direct gamma counting
• For relatively high radon concentration in water
  (gt 500 pCi/L), it is possible to determine the
  radon concentration by counting gamma rays from
  radon daughter decay using standard gamma-ray
  spectroscopy techniques with a Ge(Li) detector.
  The original radon concentration can be
  distinguished from the radium-226 concentration
  by repeating the count after 30 days, at which
  time the original radon will have virtually all
  decayed and the only remaining radon is that in
  secular equilibrium with radium-226.

http//enhs.umn.edu/hazards/hazardssite/radon/rado
nmeasure.html
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Recommended Exposure Limits For Radon-222

• Miners Safety and Health Act (underground miners)
• No worker exposure to air containing 100 pCi/L of
  radon progeny
• Annual exposure limited to no more than 400 pCi/L
  per year
• Occupational Safety and Health Administration
  (all other covered workers)
• Exposure limited to 30 pCi/L based on continuous
  workplace exposure of 40 hrs/wk and 52 wks/yr
• Environmental Protection Agency (residential
  recommendations)
• year-long average radon exposure of less than 4.0
  pCi/L in any livable area of a home

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Radon-resistant construction techniques

• Gas Permeable Layer
• Placed beneath the slab or flooring system to
  allow the soil gas to move freely underneath the
  house usually, a 4 layer of clean gravel.
• Plastic Sheeting
• Placed on top of the gas permeable layer and
  under the slab to help prevent the soil gas from
  entering the home.
• Sealing and Caulking
• All openings in the concrete foundation floor are
  sealed to reduce soil gas entry into the home.
• Vent Pipe
• A 3 or 4 gas-tight or PVC pipe (commonly used
• for plumbing) runs from the gas permeable layer
• through the house to the roof to safely vent
• radon and other soil gases above the house.
• Junction Box
• An electrical junction box is installed in case
• an electric venting fan is needed later.

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References

• http//www.epa.gov/radon
• http//www.epa.gov/radiation/radionuclides/radon.h
  tm
• http//www.atral.com/U2381.html
• http//enhs.umn.edu/hazards/hazardssite/radon/rado
  nintro.html
• http//www.cdc.gov/CANCER/lung/statistics/risk_sta
  te.htm