Geology and Soil Mechanics, UW-Stout
Radon Fact Sheet for Construction
Radon (
Rn, or its
isotope 
Rn) are decay products of the naturally occurring
radioactive elements uranium and thorium. Radon is an inert gas and usually diffuses out
into the air from the ground (soil or permeable rocks). Radon is also radioactive and
decays to a sequence of alpha particle emitters (alpha particle radiation is very
ionizing, but not very penetrating). The largest danger arises from the inhalation of
Radon and the radiation exposure to the lungs. The dose received by individuals depends
upon building materials, type of construction, subsoil, and building ventilation.
Average Radon concentration in US homes is 50 Bq/m3. The EPA
recommends remedial action if the concentration is above 150 Bq/m3 per year.
(The unit Bq stands for Becqerel and the unit Ci stands for Curies. Note
that 150 Bq/m3 = 4 pCi/L. Some other useful information
includes: 1 Bq = 1 radon decay per
second, 1 pCi = 1x10-12 Ci, 1 dm3=1 L, 1000 dm3 = 1 m3,
1 Ci = 3.7x1010 radon decays per second.)
It is estimated that 6% of all homes exceed the EPA guidelines.
About 100,000 US homes have a concentration about 10 times the average.
A few (on the order of single digits) homes have been found to have concentrations as high
as 100,000 Bq/m3. Concentrations of 100,000 Bq/m3 pose a 25%
lifetime residency risk of dying from cancer as a result of exposure to this level of
Radon.
Radon gas enters a home through natural convection (low pressure
inside/high pressure outside) between the indoors and outdoors. Even when windows are
closed, as in winter, air enters and leaves through ordinary imperfections in the building
shell - cracks around windows and doors, openings for wiring and plumbing, cracks in the
floors or walls from a variety of causes (some include soil foundation settlement,
expansion and contraction from temperature changes). This air convection is estimated to
exchange the air in a typical house about once an hour.
Primary contributors to radon gas concentrations: radium
concentration in the soil, the permeability of the soil and house understructure
to gas flow, and the leakiness of the house shell.
Remediation methods: Sealing cracks in understructure, a
fan-and-pipe system that pressurizes or depressurizes the layer of soil or gravel existing
immediately beneath the substructure (or ventilates existing sump and drain-tile systems),
extended surface filters, electrostatic precipitators, negative-ion generators.
[It should be noted that quantifying the health risks of low level
exposures to radon gas has been difficult. Public policy has traditionally followed the
linear, no threshold model. This model simply states that the more exposure (no matter
what level) the higher your health risks. Scientific studies on laboratory rats and atomic
bomb survivors (Hiroshima and Nagasaki) suggest that a very small exposure may
reduce your health risks! In other words, you would have a higher health risk from no
exposure as compared to a little exposure.]
USGS On-line book The Geology of Radon
by by James K. Otton, Linda C.S. Gundersen, and R. Randall Schumann
** Most of the information for this sheet comes from a Physics Today
(April 1989) article "Earth, Air, Radon and Home" written by Anthony Nero - a
senior scientist with Lawrence Berkeley Laboratory’s indoor-environment program.
For questions or comments regarding these pages contact Dr. Alan
Scott / scotta@uwstout.edu / this page was last updated July 09, 2002