NRPP RMP key terms

The unit used in the United States to express radon concentration in air, meaning one trillionth of a curie of radioactive decay activity per liter. Federal guidance treats 4 pCi/L as an action level for mitigation.

The SI unit of radon activity concentration, equal to one radioactive decay per second in a cubic meter of air. One pCi/L equals 37 Bq/m3, so international data must be converted before comparison.

The time required for half the atoms of a radioactive substance to decay. Radon-222 has a half-life of about 3.8 days, long enough to migrate indoors but short enough to reach equilibrium with its decay products.

The radioactive noble gas produced by decay of radium-226 in the uranium-238 series. It is colorless, odorless, chemically inert, and the isotope of concern in most indoor radon investigations.

The short-lived solid isotopes formed as radon-222 decays, including polonium-218, lead-214, bismuth-214, and polonium-214. When inhaled, these attach to lung tissue and deliver most of the radiation dose.

A radioactive solid in the uranium decay chain that decays into radon-222. Its concentration in soil, rock, and some building materials largely determines how much radon can be produced nearby.

The release of radon atoms from solid material into surrounding pore spaces or air as the parent radium decays. Only radon that escapes the grain can migrate and potentially enter a building.

A measure of the potential alpha energy of short-lived radon decay products in a liter of air, defined as any combination totaling 1.3 x 10^5 MeV. It is used to express decay product exposure rather than gas concentration.

The ratio of measured decay product activity to the activity expected if decay products were in full equilibrium with the parent radon. Values below 1 reflect losses from ventilation, plate-out, and deposition.

Movement of soil gas into a building caused by a pressure difference, typically from stack effect, exhaust fans, or wind, with the building acting as a low-pressure zone that draws soil gas through openings.

The upward movement of indoor air caused by warm air rising and escaping high in a building, which creates negative pressure at lower levels. This pressure pulls soil gas through foundation openings.

A condition in which indoor air pressure is lower than pressure in the soil or outdoors, causing air and soil gas to be drawn inward. Diagnostic testing uses fan-induced depressurization to simulate worst-case conditions.

The process by which radon-bearing soil gas or water-derived gas moves from outside or below a building into occupied indoor space through cracks, joints, drains, sumps, and other pathways.

A perimeter system of perforated pipe around a foundation that collects groundwater. When connected to interior spaces, it can serve as a major radon entry route and is often targeted during mitigation.

A pit or basin at the lowest point of a basement or crawlspace that collects water and houses a sump pump. An open or poorly sealed pit can act as a direct entry point for soil gas.

Test conditions in which exterior doors and windows are kept closed for a specified period before and during measurement, with normal HVAC operation. These conditions represent typical occupied use and are required for most short-term tests.

A radon measurement conducted for a period of a few days to about 90 days, commonly using charcoal or electret devices. Results guide decisions about follow-up testing or mitigation.

A radon measurement lasting more than 90 days, typically using alpha track or electret devices. Because it averages seasonal variation, it better estimates the year-round average concentration.

A passive integrating radon device in which radon decay ionizes air and discharges a charged electret. The voltage drop, measured before and after exposure, indicates the time-integrated radon concentration.

A passive device using a plastic film that records alpha particle tracks from radon decay over months. Etching and counting the tracks yields a long-term average radon concentration.

An electronic device that samples air and measures radon or decay products at intervals, storing time-series data. Its records can reveal tampering, unusual ventilation, or non-steady conditions during a test.

Features or data patterns that indicate whether a test device was moved, opened, or exposed to abnormal conditions. Monitors may record motion, power loss, or unusual temperature and pressure changes.

Rules for locating a measurement device, such as placing it in the lowest livable level, away from exterior walls, drafts, heat sources, and moisture, and at a specified height above the floor.

A quality assurance procedure in which a device is exposed to a known radon concentration, often in a chamber, to verify that its reported result agrees with the reference value within acceptance limits.

Two devices deployed side by side at the same location and time to assess precision. The difference between results is compared with a predetermined acceptance criterion based on concentration.

An unexposed or field-handled device used to detect contamination or background signal unrelated to radon exposure. Blank results should remain below a defined threshold.

A written document describing the procedures, responsibilities, and acceptance criteria used to ensure reliable measurements. It covers calibration, duplicates, spikes, blanks, audits, and corrective actions.

The degree to which repeated measurements under similar conditions agree with each other. In radon testing, precision is evaluated through duplicate devices and expressed against a relative or absolute criterion.

A systematic departure of measured values from the true value in one direction. Bias is assessed with spikes and reference comparisons, while random error is assessed with duplicates.

The process of comparing an instrument's response with a known reference standard and adjusting or documenting its accuracy. Devices must be calibrated on a schedule specified by the program.

The radon concentration at which mitigation is recommended, commonly 4 pCi/L in the United States. It is not a strict safety threshold; lower concentrations still carry some risk.

Building modifications that reduce indoor radon concentrations, such as sub-slab depressurization, sealing, and ventilation. Post-mitigation testing verifies that the reduction was achieved.

A mitigation method that uses a fan and piping to draw soil gas from beneath the slab and vent it outdoors, lowering pressure under the floor so soil gas does not enter the building.

A published procedure describing how radon measurements or mitigation should be performed, including device placement, test duration, and reporting. Following the applicable protocol supports defensible results.

A situation in which a tester's financial or personal interest could bias results, such as testing and mitigating the same property. Disclosure and separation of roles protect objectivity.

Obtaining a client's clear agreement to testing procedures, limitations, and use of results before work begins. It includes explaining that no test can guarantee a specific exposure level.

The process of explaining test methods, results, uncertainty, and recommended next steps in plain language. Effective communication helps clients make informed decisions without overstating or minimizing risk.

Changes in indoor radon concentration across the year caused by weather, heating, ventilation, and soil moisture. Short-term results may differ from the annual average because of this variation.