What Is Radon?
Radon is a naturally occurring, radioactive noble gas produced by the decay of uranium in soil. It’s colorless, odorless and tasteless, and can enter indoor spaces through leaky spots in buildings (e.g. cracks in the foundation). There are two relevant isotopes of radon — Radon-222 and Radon-220 (thoron) — both are captured by the air-Q Radon measurement module.
Radon can accumulate especially in poorly ventilated basements. Long-term exposure to high radon levels increases the risk of developing lung cancer.
EU guidelines set the legal limit at 300 Bq/m³, the WHO already at 100 Bq/m³. In general, the less radon exposure you’re subjected to, the better.
1. Patented air-Q Radon Module
When radon decays, alpha radiation (α particles) is emitted. This consists of helium nuclei (2 protons, 2 neutrons) and has a very short range (a few centimeters in air), but a high ionization effect.
After several years of development, we were able to create our own radon measurement module. Radon is quantified here by detecting light pulses from a scintillator material. The α particles are then detected indirectly via their interaction with the scintillator, which produces flashes of light when hit by ionizing radiation — these flashes are counted and thereby measured. The scintillator is used in a gas-permeable but light-tight measurement chamber. The flashes of light are captured by a highly sensitive modern photon sensor, a so-called SiPM (Silicon Photomultiplier), which is able to detect even individual photons. The number of light flashes (equal to radon decay events) per unit of time reveals the radon concentration and is converted into becquerels per cubic meter. The developed radon module has a patent pending (EP23176915.9 / 4 471 462).
2. Calibration of the Radon Measurement Module
Our radon modules are individually calibrated at our factory using measuring devices tested according to DAkkS (German accreditation body) guidelines at a calibration lab (Sarad). The calibration references were tested and calibrated for 300, 3,000 and 30,000 Bq/m³. Every air-Q goes through a complete measurement cycle spanning several days and receives individual calibration values for sensitivity and baseline. Testing follows strict, standardized procedures to ensure accuracy, repeatability and linearity.
3. Challenges in Measuring Radon
a. Measurement speed and accuracy vs. sensor size
One becquerel means one radioactive decay event per second. The usual unit of measurement is becquerel per cubic meter — for example, the German Federal Office for Radiation Protection sets a limit of 300 Bq/m³. Radon meters are typically expected to be much more compact and even portable, so measurement happens in a volume far smaller than 1 cubic meter (a 1×1×1 meter cube) — e.g. 200 cm³ (0.0002 m³). If you want to measure with a sensor with a small measurement chamber, response behavior, measurement resolution and accuracy decrease accordingly. The challenge is to develop a measurement chamber or method that allows for a high-quality, comparable real-time measurement. For the air-Q Radon, we therefore opted for a relatively large chamber. In addition, the measurement module uses optimized passive ventilation of the measurement chamber, so it can deliver readings in a relatively short time that also respond quickly to environmental conditions such as ventilation.
To illustrate how many decay events per measurement volume need to be measured, we’ve put together an overview here. For example, 50 Bq/m³ corresponds to 3,000 radioactive decays per cubic meter, but only 0.6 decays per minute.
Radioactive decays per measurement volume per minute
Radon concentration → decays/minute (1 m³ · 200 cm³)
50 Bq/m³ — 1 m³: 3,000 · 200 cm³: 0.6
100 Bq/m³ — 1 m³: 6,000 · 200 cm³: 1.2
300 Bq/m³ — 1 m³: 18,000 · 200 cm³: 3.6
1,000 Bq/m³ — 1 m³: 60,000 · 200 cm³: 12
b. Averaging algorithm necessary for measurement in small volumes
Radioactive decays are statistical processes. There’s therefore a certain probability of a decay event. At low radon exposure, one more or fewer radioactive decay in a small measurement volume can mean a doubling/halving of the reading (and thus a possible over- or underestimation of the actual radon exposure). An averaging mechanism is therefore necessary to obtain a steady measurement curve. At the same time, averaging leads to worse response behavior. That’s why a sophisticated mechanism is needed. For the air-Q Radon, a customized Kalman filter was used.
The air-Q Kalman filter helps calculate the most accurate possible estimates from just a few data points. It combines past values and trends with current readings. Each new measurement is used to improve the previous estimate. The filter works step by step and continuously updates its estimate with each new piece of information.
c. Measuring radon and thoron
Most radon meters are designed/calibrated for Radon-222. It’s the most common radon isotope and thus, in practice, the greatest health hazard.
Building materials that may contain thorium can potentially emit thoron (Radon-220). These include, for example, clay plaster, pumice, natural gypsum, tuff, or fly ash cement. Thoron escapes at the surface and decays extremely quickly due to its short half-life (55 seconds). This means it can only move a few centimeters away from the material in that time, and is only measurable in the immediate vicinity of the aforementioned building materials. The air-Q Radon measurement module cannot distinguish between Radon-222 and Radon-220, and outputs both as the "radon" reading.
Certified Quality
The WELL Standard is an international rating system for building certification, developed and regulated by the Well Building Institute (IWBI) in the USA. It is the first standard of its kind focused exclusively on the health and wellbeing of people in buildings, setting high standards for it. The air-Q meets the high demands WELL places on air quality monitoring and is certified by the IWBI.
Our Partners in Sensor Development
Together with many partners, we develop the air-Q air analyzer and the air-Q app to improve people’s health and performance. Our development partners are especially important here, with whom we work daily on new solutions for healthy, conscious breathing and living.
