NRSB RMT key terms

A colorless, odorless, radioactive noble gas produced by the decay of radium-226; it seeps from soil and rock into buildings and is the leading environmental cause of lung cancer after smoking.

The short-lived solid decay products formed after radon decays, including polonium-218, lead-214, bismuth-214, and polonium-214; these emit alpha particles and deliver most of the lung dose.

A radioactive metal in the uranium-238 decay chain with a 1,600-year half-life; it decays into radon gas and is the parent nuclide that supplies radon in soil and building materials.

The long-lived primordial isotope that begins the decay series leading through radium-226 to radon; its concentration in underlying rock and soil largely determines regional radon potential.

The time required for half the atoms of a radioactive substance to decay; radon-222's 3.8-day half-life lets it migrate from soil into buildings but limits how far it travels.

The probability per unit time that a given radioactive atom will decay, equal to the natural logarithm of two divided by the half-life; used in activity and equilibrium calculations.

The SI unit of radioactivity equal to one nuclear transformation per second; radon concentrations are often reported in becquerels per cubic meter (Bq/m3).

The customary U.S. unit for radon gas concentration in air, where one picocurie equals 0.037 becquerels; U.S. action and mitigation decisions are usually expressed in this unit.

A historical unit describing the concentration of radon progeny that releases a defined amount of potential alpha energy per liter of air; it applies to decay products, not to radon gas itself.

A cumulative exposure unit equal to breathing air at one Working Level for 170 hours; it combines progeny concentration and time and is used in occupational and epidemiological dose estimates.

The total alpha energy that would be released as a radon progeny mixture decays to long-lived lead-210; it is the physical quantity underlying Working Level measurements.

A steady condition in which a parent nuclide's half-life is far longer than its progeny's, so progeny activity equals parent activity; radon and its short-lived progeny approach this state in closed spaces.

The ratio of measured radon progeny activity to the radon gas activity present; values below one reflect ventilation, plate-out, or dust conditions that shift progeny away from equilibrium.

Deposition of charged radon progeny onto walls, floors, and furniture, removing them from the breathing air; it lowers measured progeny concentrations and affects equilibrium assumptions.

The radon concentration at which mitigation is recommended; U.S. guidance sets 4 pCi/L for homes and 2 to 4 pCi/L as a range for considering action in schools and workplaces.

The 4 pCi/L indoor radon threshold in U.S. Environmental Protection Agency guidance; results at or above it generally prompt confirmatory testing and consideration of mitigation.

A prediction of the indoor radon concentration a building could reach based on geology, soil, and construction factors; it is mapped by region and does not replace measurement of an individual building.

A classification of geographic areas by predicted average indoor radon potential, commonly zone 1 (highest), zone 2 (moderate), and zone 3 (low); it guides testing priorities, not individual building conclusions.

A radon measurement lasting from a few days to about 90 days, typically using charcoal or electret devices; it gives a quick screening result but is more sensitive to weather and seasonal variation.

A radon measurement lasting more than 90 days, usually with alpha-track detectors; it averages seasonal swings and better estimates the year-round concentration a occupant actually experiences.

Test protocols requiring exterior doors and windows kept closed and permanent ventilation shut for a set period before and during sampling, so results reflect normal occupied conditions without excess ventilation.

A second measurement made after an initial short-term result at or above the action level, intended to confirm the concentration before a mitigation decision is made.

Choosing detector locations that represent breathing-zone conditions, such as the lowest livable level, away from exterior walls, drafts, heat sources, and moisture, while avoiding kitchens and bathrooms.

The documented set of procedures for device deployment, exposure duration, retrieval, and documentation that must be followed so results are valid and defensible.

A written record tracking each detector from deployment through shipping, analysis, and reporting, showing who handled it and when so results can be trusted in legal or real estate contexts.

A written program of procedures, responsibilities, and checks ensuring measurements meet defined accuracy and precision goals; it includes calibration, blanks, spikes, duplicates, and audits.

The routine operational checks that verify individual measurements, such as blanks, duplicates, spikes, and calibration verification, and flag results that fall outside acceptance criteria.

A detector or sample dosed with a known amount of radon or progeny to verify that the measurement system recovers the expected value within acceptance limits.

An unexposed detector carried and shipped alongside field devices but not deployed for sampling; its result reveals contamination, handling errors, or background in the measurement process.

Two detectors deployed at the same location for the same period to assess measurement precision by comparing their reported results.

The degree to which repeated measurements under the same conditions agree with each other; it describes random variability and is distinct from accuracy, which concerns closeness to the true value.

How close a measured result is to the true radon concentration, reflecting systematic and random error combined; it is assessed through spikes, calibrations, and reference comparisons.

The process of comparing an instrument or detector response against a known reference standard traceable to a national source, and adjusting or correcting results accordingly.

An unbroken documented chain linking a measurement result to recognized national or international standards through successive calibrations, establishing the credibility of reported values.

A passive short-term device in which activated charcoal collects radon for days, then laboratory analysis measures the collected activity; exposure timing and moisture strongly affect results.

A passive long-term device in which alpha particles from radon and progeny leave microscopic tracks in a plastic film, which is etched and counted to estimate average concentration over months.

A passive device that measures radon through voltage change on a charged electret caused by ionizing radiation inside a chamber; usable for short- or long-term exposures with proper calibration.

An electronic instrument that samples air and reports radon concentration at intervals, providing time-series data useful for detecting tampering, ventilation changes, and diurnal patterns.

Building modifications that reduce indoor radon entry or concentration, such as sub-slab depressurization, sealing, or ventilation; testing verifies whether the chosen approach actually works.

A measurement performed after a mitigation system is operating, conducted under defined conditions, to confirm that indoor radon has been reduced below the action level.