Radon Science and Health Effects
This domain tests the physics and health basis behind radon testing: what radon is, how exposure becomes dose, and which thresholds drive recommendations.
Radon and its decay chain
Radon-222 is a colorless, odorless, radioactive noble gas in the uranium-238 series. It forms when radium-226 decays in soil, rock, and some building materials. Its half-life is about 3.82 days-long enough to travel from soil into a building, short enough that its decay products accumulate indoors. The main lung hazard comes from short-lived alpha-emitting progeny such as polonium-218 and polonium-214, which can attach to particles or remain unattached and deposit in the bronchial epithelium.
Health risk
Residential radon is an established lung carcinogen. In the United States it is widely described as the second leading cause of lung cancer after smoking, with an EPA estimate of about 21,000 radon-related lung cancer deaths per year. Risk rises with concentration and duration; smoking multiplies the absolute risk. EPA's action level is 4 pCi/L (148 Bq/m³). It is a decision level, not a safe/unsafe line. WHO's reference level is 100 Bq/m³.
Units and conversion
1 pCi/L = 37 Bq/m³.
Worked example
A report states 200 Bq/m³. Convert: 200 ÷ 37 = 5.4 pCi/L. This exceeds both the EPA action level (4 pCi/L) and the WHO reference level (100 Bq/m³). The reasoning is to convert first, compare in one unit system, and remember that 200 is not a pCi/L value.
Traps
Treating 4 pCi/L as a health guarantee; confusing radon gas with its alpha-emitting progeny; using 3.7 instead of 37 for the conversion; and assuming a short test proves a home is permanently low.