Post on 11-Jan-2016
transcript
Field Methods
Rado
Copyright © 2012 by DBS
Contents
• What is radon?
• Health effects
• Radon risks
• Testing and Remediation
What is Radon?Natural Radioactivity
22286Rn
Invisible, odorless, colorless, tasteless
Only gas in 238U decay chain
220Rn from 232Th has 55s t1/2
What is Radon?Radon Gas50 minutes
26.8m
What is Radon?Natural Radioactivity
Source: http://energy.cr.usgs.gov/radon/DDS-9.html
What is Radon? Stanley Watras
• Limerick Nuclear Power Plant, Christmas 1984
• Set off radiation alarm bells• Home basement Rn ~
100 000 Bq m-3 • Risk equivalent smoking 135
packs of cigarettes per day
Designed to detect radiation on workers leaving…Watras was entering!
What is Radon? 1988 EPA orders every home tested
What is Radon?
What is Radon?
• Radon is a gas
• It is naturally occurring
• You cannot see or smell it
• It enters buildings from the soil via diffusion (concentration gradient)
Uranium
Radium
Radon
1,600 years
4.5 billion years
Question
Radon is said to be a daughter of radium-226, polonium-218 is a daughter of radon. Why are these not called sons?
Radon decay products (RDP’s) continue to decay giving birth to new daughters (progeny).
Indeed these RDP are the real culprits in the radon story!
What is Radon? Stack Effect
• Warm air rises and escapes home
• Pressure difference inside-outside
• Replacement air drawn in from below
• Increases with wind speed
http://www.cornwallradon.co.uk/page21.html
Stack effect enhances Rn movement
What is Radon?Spatial Distribution
• Radon enters from beneath foundation and travels upward
• Diluted with outdoor air infiltrating building
10
< 5
5-6
Health EffectsRadon Gas
Progenies (‘daughters’) build up in confined space –are breathed in, stick to surface of airways and emit α-particles
Radon Progeny
218Po and 214Po deliver the radiologically significant dose to the respiratory epithelium
Lead-210
Polonium-214
Bismuth-214
Lead-214
Polonium-218
Radon-222
ββ, , γγ
αα,,γγ
αα,,γγ
αα,,γγ
ββ, , γγ
Lead-206
Polonium-210
Bismuth-210
ββ, , γγ
ββ, , γγ
22 yrs22 yrs
4 day
3 min
27 min
20 min
0.2 ms
5 day
138 day
Stable
αα,,γγ
Health Effects Alpha Decay
4He Nucleus Ejected from 222Rn Nucleus
+2+2
4He + He + 218PoPo
+
+
+
+
+
+
+
+
+
Radon - 222Radon - 222
alpha alpha particleparticle
Highly energetic α, β particles rip through tissue causing cellular and genetic damage
Health Effects Interaction with DNA
• Highly radioactive particles adhere to lung tissue, where they can irradiate sensitive cells
• Radiation can alter the cells, increasing the potential for cancer
Double Strand Breaks+ ionize water to produce free radicals
NCRP 93 (1987)
Natural (mrem)Radon 200Cosmic 27Terrestrial: -external 28 -internal 39
Artificial (mrem)-Diag. X-rays 39-Nuc. Med. 14-Consumer Pro. 10-Other ~1TOTAL ~360
Radon delivers > 50% radiation dose
Radon Risks Radon Levels
http://energy.cr.usgs.gov/radon/georadon/2.html
GW > Soil > Indoor Air > Outdoor Air
Outdoor?
Radon Risks
• Average Rn concentration inside a home 1 pCi L-1
• Roughly 2 decays per minute
• 1 Working Level (WL) = 100 pCi L-1
(defined for no ventilation or walls)• Effect of removal can be taken into account by x2 WL = 200 pCi
L-1, thus 1 WL = 200 pCi L-1 at home
WL = qRn / 200
e.g. 1 pCi L-1 = 0.005 WL
Question
Convert pCi L-1 to dpm L-1
1 Ci = 3.7 x 1010 dps
60 secs in 1 minute
1 pCi = 0.037 dps x 60
= 2.22 dpm
Health Effects Group A Carcinogen
• Radon is ranked as a Group A carcinogen
– Highest ranking for cancer potential
– Known to cause lung cancer in humans
– Tobacco smoke and tobacco products in same category
• Long-term exposure increases chances
– Risk of lung cancer in normal life = 1-2 % (10-20 in 1000)
– Risk of lung cancer at 1 pCi = + 0.3-1.3% (3-13 in 1000)
Health EffectsEpidemiology
• ALA, AMA and Surgeon General all recommend reducing indoor Rn
• 15,000 – 22,000 deaths a year• Epidemiology confirmed by NAS, WHO, NCRP• Combined effects of Rn and smoking particuarly dangerous
2nd hand smoke!
Health Effects Human Studies
• How do we know radon is a carcinogen?
• NCI study examined 68,000 uranium miners
• Miners die at a rate 5 x general population
Dose (rem)
Ad
vers
e H
ea
lth E
ffect
s
Atomic Bomb Survivors
Medical Patients
Observed EffectsObserved EffectsObserved EffectsObserved Effects
? ?
?
Underground MinersUnderground Miners
Linear
No threshold
Health EffectsBiological Effects of Ionizing Radiation (BEIR) VI (1999)
• Risk estimates based primarily on radon-exposed miners
• Est. 15,000 – 22,000 lung cancer deaths each year in the U.S. from residential exposure
• 10-15% of all lung cancer deaths in US (150,000)
• Confirms 2nd leading cause
02000400060008000100001200014000160001800020000
U.S
. L
un
g C
ance
r D
eath
s/yr
Smokers Non-Smokers
Health Effects Comparing Radon Related Cancer
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
An
nu
al U
.S.
Can
cer
Dea
ths
Lung Cancer (radon)
Liver Cancer
Brain Cancer
Stomach Cancer
Melanoma
Oral Cancer
Gallbladder Cancer
Bone Cancer
Health Effects How Radon Compares To Other Causes Of Death
0
5,000
10,000
15,000
20,000
25,000
Dea
ths
per y
ear
Low
er e
stim
ate
Drunk Driving
Drownings Fires/Burns Air Transportation
Radon
Upp
er
estim
ate
Source: U.S. EPA’s Home Buyer’s and Seller’s Guide (Radon: National Academy of Sciences, Non-radon: National Safety Council)
Health Effects Radon and Smoking
Darby et al., 2004
Question
Convert pCi L-1 to Bq m-3
1 pCi L-1 x 1000 L m-3 = 1000 pCi m-3
1000 pCi m-3 x 3.7 x 1010 Bq / Ci
= 1 x 10-9 Ci m-3 x 3.7 x 1010 Bq / Ci
= 37 Bq m-3
Health Effects Radon Risks
Comparing Rn cancer rates to rates for smokers
20x
Turko, 2002
Basement level
Radon-222Zone 1: > 4 pCi/L (red)
Zone 2: 2-4 pCi/L (orange)
Zone 3: < 2 pCi/L (yellow)
Based on indoor measurements, geology, aerial radioactivity, soil parameters and foundation type
End
• Review
Testing and RemediationFrequencies of 222Rn in US Homes
Radon levels depend on:• Radon strength in soil• Soil porosity• Building to soil pressure difference• Building ventilation rate• Openings into the soil
Testing and RemediationFrequencies of 222Rn in US Homes
8 million homes
Types of Measurement
• Continuous• Integrated long and short term• Multiple• Single 1-7 day – ‘screening’
All rely on measurement of emitted radiation
Testing and RemediationTesting
Alpha Track
Photovoltaic Alpha-track Sensor
Charcoal
Testing and RemediationTesting
Alpha Track
Alpha-tracks are plastics - microscopic radiation tracks after chemical treatment
Magnified only 100 times3 months at EPA Action Level of 4 pCi/L
These are pits in CR-39 plastic made by alpha particles. If they can make these pits in plastic, imagine what they can do to your DNA
Testing and RemediationTesting
Sun-NuclearPhoto-diode – EPA verified continuous monitor
Detects radon’s α-particle with 5.590 MeV energy. Works by measuring the voltage change across an P-N semiconductor bridge.
Factors Affecting the Emission of Radon
• Frost, rain, asphalt caps soil – stack effect exerted on larger area
• Wind
Factors Affecting the Emission of Radon
What interpretation can you provide for the data in Fig. 1?
Factors Affecting the Emission of Radon
• Concentration varies continuously
• High in winter• Low in summer
Testing and RemediationRadon Mitigation
• Active Soil Depressurization (ASD)
– Creates a vacuum beneath the foundation
• Caulking and sealing
• Ventilation
http://www.radon-services.com/animations/animation.htm
Testing and RemediationPassive System
Large gravel beneath slab
Polyethylene soil-gas retarderbetween slab and gravel
Sealing and caulking
Vent pipe running betweensub-slab gravel and roof
Junction Boxes(to power fan and warning device, if needed)
Key Findings
• Studies of uranium miners implicated radon as a known cause of lung cancer in humans
• Recent residential studies have provided direct evidence of increased lung cancer risk due to radon
• Suggest radon may play a role in 10% of all lung cancer deaths
• Nearly ¾ of radon-associated deaths occur among smokers
• Radon is an avoidable risk
Rebuked
• http://www.seered.co.uk/radon_newsci.htm
• http://removeradon.com/articles.htm
Further Reading• Cothern (1999) Indoor Air Radon. Environmental Geochemistry and Health, Vol. 21, No. 1, pp. 83-90.
• Darby S., Whitley E., Silcocks T., Thakrara B., Green B.M.R., Lomas P.R., Miles J.C.H., Reeves G., Searn T. and Doll R., (1998) Risk of lung cancer associated with residential radon exposure in South - West England: A case-controlled study. British Journal of Cancer, Vol. 78, No. 3, pp. 394-408.
• Hess C.T., Weiffenbach, C.V., and Northon, S.A. (1983) Environmental radon and cancer correlations in Maine. Health Physics, Vol. 45, No. 2, pp. 339-348
• Krafthefer B. (1984) Measurements of radon decay products in residential environments, Ashrae Journal - American Society of Heating, Refrigeration and Air-Conditioning Engineers, Vol. 26, No. 5, pp. 55.
• Harley N.H. (1984) Radon and lung cancer in mines and homes, New England Journal of Medicine, Vol. 310, No. 23, pp. 1525-1527.
• Joyce C., Kenward M. and Pearce F. (1986) Perils in the all-American home, New Scientist, Vol. 110, No. 1511, pp. 22-23.
• Pearce F. (1987) A deadly gas under the floorboards, New Scientist, Vol. 113 (1546), pp. 33-35.
• Oge M. (1994) The US environmental agency`s strategy to reduce risks of radon, Radiation Protection Dosimetry, Vol. 56, No. 4, pp. 343-354.
• Phillips P.S. and Denman A.R. (1997) Radon: a human carcinogen. Science Progress, Vol. 80, No. 4, pp. 317-336.
• Phillips P.S., Denman A.R., and Barker S. (1997) Silent, but deadly. Chemistry in Britain, Vol. 33, No. 1, pp. 35-38.
Books
• Brookins, D.G. (1990) The Indoor Radon Problem. Columbia University Press.
• Cole, L.A. (1994) Element of Risk: The Politics of Radon. Oxford University Press.
• Cothern, C.R., and Smith, J.E Jr. (1987) Environmental Radon. Springer.
• Durrani, S.A., and Radomir, I. (1997) Radon Measurements by Etched Track Detectors : Applications in Radiation Protection, Earth Sciences and the Environment. World Scientific Publishing Company.
• National Research Council (1989) Health Effects of Exposure to Radon. BEIR IV. National Research Council.
• Nazaroff, W. and Nero, Jr., A. (1988) Radon and its Decay Products in Indoor Air. Wiley, New York.
Modeling Radon ExposureBox Model
Q = S τ
q = Q / V = Sτ / V
Source
S
Sink
L
V
Q
q
Q = quantity
q = concentartion
Modeling Radon ExposureSources and Sinks
Sources,
SRn = 0.01 – 10, mean = 0.5 pCi L-1 h-1
Background concentration, q0Rn = 0.2 pCi L-1
Residence time of air in the home, τvBackground gas ventilation rate (per unit voume),
Sv = Q0 = q0Rn
V V τv τvSinks,
Ventilation loss rate, Lv = qRn / τv (qRn = Rn concentration inside)
Decay loss rate, Ld = qRn / τRn (τRn = half-life = 91 hrs)
Steady-state: SRn + Sv = Lv + Ld
Question
SRn + Sv = Lv + Ld
SRn + q0Rn / τv = qRn / τv + qRn / τRn
Rearrange to find qRn
qRn = q0Rn + τv SRn
1 + τv / τRn
Modeling Radon ExposureRadon Concentration
SRn + Sv = Lv + Ld
SRn + q0Rn / τv = qRn / τv + qRn / τRn
qRn = q0Rn + τv SRn
1 + τv / τRn
Usually simplified: qRn ≈ q0Rn + τv SRn (denominator = 1)
Since: q0Rn = 0.2 pCi L-1, SRn = 0.01 - 10, mean = 0.5 pCi L-1 h-1
and τv = 1 hr
qRn = 0.7 pCi L-1
Rn concentrations are clearly dependent on source and ventilation!
Modeling Radon ExposureRadon Concentration
qRn ~ q0Rn + τv SRn
• With fast ventilation τv = 0, qRn ≈ q0Rn (depends on outside air
conc.)
• With no ventilation τv = ∞, qRn ≈ τRn SRn (depends on source and t1/2)