Radioactivity in the environment

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Radioactivity in the environment

• Michael McNaughton
• For the Community Radiation Monitoring Group
• Wednesday, December 10th, 2009

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Radioactivity in the environment

• Response to the GAP Report
• Radioactivity in indoor dust
• Radioactive material downwind of LANL
• Can we tell where it came from?
• Is indoors different from outdoors?
• What are the potential health effects?
• Detailed calculations and references are
  available.

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3 categories of radioactive material

• Natural radioactivity
• Radon, potassium-40, uranium, thorium
• Global fallout from testing
• Cesium-137, strontium-90, plutonium, americium
• LANL radioactive materials
• Tritium, plutonium, americium, depleted uranium,
  cesium-137, strontium-90, cobalt-60

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Variability

• The concentrations of natural radioactivity vary
  greatly.
• High concentrations may be natural, or from
  global fallout, or from LANL.
• It is not possible to establish background
  concentrations.

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Potassium-40 in soils large variations
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Thorium in soils large variations
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Uranium in soils large variations
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NM Mining Districts

• Uranium
• Forest
• Metals
• Other

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Aerial Gamma Survey of LANL
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LANL has been extensively studied

• More than 99 of radioactivity detected on the
  surface is from natural sources
• Radionuclides are identified by spectroscopy
• Mostly natural potassium-40, thorium, and uranium
  decay products
• Pink, red, and black are LANL radioactivity

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Gamma Spectroscopy
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Downwind
No measurable effect from airborne deposition
source
5.0
Miles
1.0
Rio Grande
Sangre de Cristo
LANL

• Downwind concentrations depend on distance
• Calculations and observations show deposition (in
  soil and sediment) of airborne radioactive
  material is too small to measure beyond 1 mile.

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Plume from Cerro-Grande Fire
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Plume from Cerro-Grande Fire
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Plumes from known LANL sources extend less than 1
mile.
No visible deposition plume down wind from
potential LANL dust sources
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Indoor dust
Most dust particles are large

• Samples from NMED/OB and Los Alamos Monitor
  offices
• Analyzed by Paragon Analytics lab
• Greater than 99 from natural sources
• Mostly radon decay products
• .08 pCi/gram from LANL at L. A. Monitor

micrometers
nanometers
Radon decay products are on small particles
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DP Road

• At Los Alamos Monitor, 0.5 of the alpha
  radioactivity is plutonium from TA-21
• Concentration 0.08 pCi/g
• Potential dose from plutonium

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LANL Contamination

• LANL airborne contamination is found only within
  1 mile of Los Alamos County
• Beyond 1 mile, calculations and observations show
  deposition of airborne contamination is too small
  to be measured
• (Waterborne LANL contaminants may be found in
  canyons downstream of historical LANL outfalls)

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Radon

• Indoors, most of the radioactivity and most of
  the dose is from radon decay products
• They are attached to very small particles
• Small particles are difficult to collect, so the
  data vary
• Short-lived activity is 50,000,000 pCi/g
• Long-lived activity is 20,000 pCi/g
• Dose from radon is 250 mrem/year

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Accumulation of radon decay products
on an AIRNET filter
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How can we determine what comes from LANL?

• Regional Statistical Reference Level (RSRL) is no
  more than a reference level
• Radioactivity can be greater than the RSRL
• In such cases, consider
• What radionuclides are prevalent at LANL?
• What isotopes are prevalent at LANL?
• Then, compare using models and calculations

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Activity can differ from RSRL

• Elevation More rain and especially snowfall
  causes more fallout at higher elevations
• Soil and rock in some regions is high in
  naturally radioactive elements such as uranium
• Runoff from less permeable slopes can focus
  fallout in basins
• Bioaccumulation concentrates radionuclides in
  plant matter
• Forest fires concentrate radionuclides in the ash

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Other data RSRL

• Higher than RSRL concentrations are measured in
  many locations, worldwide
• In Colorado, Colorado State University measured
  cesium-137 concentrations greater than those at
  Trampas Lake.
• NMED/OB investigations are continuing.

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What radionuclides are prevalent at LANL?

• Largest historical emissions from LANL are
  tritium, plutonium-239, depleted uranium
• Much larger than strontium-90 or cesium-137
• In contrast, downwind data show mostly cesium-137
  and strontium-90
• Observations are not consistent with LANL origin
• Observations are consistent with global fallout

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Cobalt-60

• Cobalt-60 was prevalent at TA-2 and TA-53
• Emissions of cobalt-60 are comparable with
  strontium-90 and cesium-137
• But cobalt-60 has not been observed outside Los
  Alamos County
• This is consistent with models and calculations
• Measurements and models show LANL airborne
  contamination is not measurable more than 1 mile
  from Los Alamos County

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What isotopes are prevalent at LANL?

• LANL higher uranium-238
• Not observed downwind of Los Alamos
• LANL higher plutonium-239
• Fallout higher plutonium-240
• Proportions of uranium-238 indicate that airborne
  radiological contamination is not measurable more
  than 1 mile from Los Alamos County
• Plutonium investigation is ongoing

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Using models and calculations

• Two models (CAP88 and Hotspot) were used to
  calculate airborne cesium-137 and strontium-90 in
  Embudo Valley
• LANL contribution is a million times less than
  the amounts observed
• Results are consistent with global fallout, not
  with LANL origin
• LANL airborne contamination is not measurable in
  Embudo Valley

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Dose

• The measure of health detriment due to
  radioactivity is the dose, measured in mrem
• The maximally exposed individual, MEI, receives
  
• Total dose from all natural and man-made sources
  is 500 mrem/year around LANL
• Some natural locations 1,000 mrem/year
• These locations are extensively studied, and
  there is no measurable health detriment

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Doses
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Sources of Airborne Radiation Exposure Around LANL
Background radiation 500 mrem/year Additional
from LANL Man-made products e.g., building materials, smoke
detectors (2)
Potassium-40 e.g., bananas, food, ash (8)
Medical and dental (10)
Cosmic radiation (13)
Terrestrial Radiation e.g., in rock, potassium,
thorium, uranium (19)
100
Radon (48)
LANL all-pathways e.g., stacks dust (0.2)
Nuclear fallout i.e., tests 1940s-60s (0.2)
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Conclusions

• We studied the Government Accountability Project
  (GAP) data
• We gathered our own data
• Almost all the radioactivity in indoor dust is
  naturally occurring
• Measurements and models show that airborne
  contamination from LANL is not measurable more
  than 1 mile from Los Alamos County
• All data show no measurable health detriment from
  LANL airborne contamination