Learn About Radon
A progressive course from atoms to indoor measurements. Understand the science of radon: what it is, where it comes from, how it travels from rock to buildings, and how to measure it.
The Radon Atom
Understanding radon as a chemical element, its cosmic origin, radioactive decay and detection physics.
What is Radon
The Radon Atom
Understanding the fundamental properties, isotopes, and physics of radon — the naturally occurring radioactive noble gas at the center of indoor air quality concerns.
Radium and Geology
The Link Between Rock Chemistry and Indoor Radon
How radium-226, continuously produced deep in the uranium-238 decay chain, becomes the critical bridge between geological processes and radon accumulation in buildings.
Radon Decay Products
What Happens After Radon Decays, and Why It Matters for Health
Understanding the chain of solid, radioactive progeny that radon produces, how they deposit in airways, and why they — not radon gas itself — deliver the carcinogenic dose that makes radon the second leading cause of lung cancer.
From Rock to Air
How radon is generated in soil, transported through the subsurface, and released from water and building materials.
Radon in Soil
From Radium Decay to Soil Gas
How radon is continuously generated in soil grains, what fraction escapes into pore spaces, and why soil characteristics control how much radon reaches building foundations.
Radon Transport
The Physics of Radon Movement Through Soil and Rock
Understanding the two fundamental mechanisms — molecular diffusion and pressure-driven advection — that govern how radon migrates from deep soil to building foundations, and why advection dominates in real buildings.
Radon and Water
The Groundwater Pathway and Water-to-Air Transfer
How radon dissolves in groundwater, reaches homes through wells and municipal supplies, and degasses into indoor air — accounting for about 1–2% of indoor radon on average, but up to 30% in high-radon groundwater areas.
Radon from Building Materials
When Construction Materials Are the Radon Source
While soil is the dominant radon source for most buildings, certain construction materials — especially those derived from uranium- or radium-bearing minerals — can contribute significantly to indoor radon, adding 5–200+ Bq/m³ depending on material type, radium content, and building ventilation.
Radon in Buildings
How radon enters buildings, accumulates in indoor air, and varies with climate, time and building operation.
Radon in Buildings
How Soil Gas Enters and Why Buildings Differ
Understanding why radon entry is dominated by pressure-driven soil-gas flow, how foundation types and building characteristics control entry rates, and why neighboring buildings can have radon levels differing by an order of magnitude despite sitting on the same soil.
Radon and Climate
How Weather and Atmospheric Conditions Drive Radon Entry
Weather affects indoor radon primarily by changing the pressure difference between soil and the building. [Stack effect](learn:radon-in-buildings) from indoor-outdoor temperature differences is the dominant driver, while barometric pressure changes, wind, [soil moisture](learn:radon-transport), and frozen ground add shorter-term modulation.
Radon and Time
Why Indoor Radon Changes From Minutes to Years
Indoor radon varies constantly because concentration reflects the balance between entry rate (driven by soil-gas pressure, stack effect, wind, and weather) and removal rate (ventilation and decay). Both change on every timescale, making no single measurement "the" radon level. Only long-term measurements (≥3 months, ideally 12 months) reliably estimate the annual average on which reference levels and health risk are based.
Measuring Radon
How radon is measured using passive and active detectors, and how to interpret measurement data correctly.
From Geology to Indoor Radon
The Complete Chain from Uranium to Lung Dose
Indoor radon represents the endpoint of a multiplicative chain spanning cosmic nucle osynthesis, planetary differentiation, radioactive decay, soil transport, building entry, and progeny behavior. High uranium content does not guarantee high indoor radon — geology explains only 10–25% of indoor radon variance because transport, entry, and building factors dominate.
Measuring Radon
Methods, Detectors, and Protocols
Radon measurement devices fall into two categories: passive integrating detectors that accumulate signal over weeks to months without power, and active continuous monitors that provide real-time readings. Each detector type measures different aspects of radon decay — some count radon gas directly, others detect alpha-emitting progeny — requiring different calibrations and applications.
Understanding Radon Measurements
Interpreting Results, Uncertainty, and Statistics
Radon concentrations follow lognormal distributions — not normal — making geometric means more representative than arithmetic means. Measurement uncertainty combines detector calibration uncertainty (~7–20%), temporal variability (dominant for short tests), spatial variability within rooms (typically 10–30%), and year-to-year variation (15–30% CV). Understanding these sources is essential for interpreting results near reference levels.
Radon Testing Strategy
Protocols, Decision-Making, and Follow-Up Actions
Effective radon testing matches measurement duration and method to the decision being made. Screening uses short-term tests for rapid risk assessment; compliance and mitigation decisions require long-term measurements; diagnostics need continuous monitoring. Understanding when to test, where to place detectors, and how to interpret results in context drives appropriate action.
Ready to Test Your Home?
Understanding the science is the first step. Learn how to measure radon levels in your home with our comprehensive testing guide.