Secondary Standard for ²²²Rn Activity in Air and Water
Radon (Rn) is a noble gas with over 30 isotopes, of which three occur naturally:
- ²²²Rn (Radon) with a half-life of 3.824 days,
- ²²⁰Rn (Thoron) with a half-life of 55 seconds,
- ²¹⁹Rn (Actinon) with a half-life of 3.96 seconds.
Origin and Health Risks
- ²²²Rn is a decay product of ²³⁸U, produced by the radioactive decay of ²²⁶Ra.
- The primary source of radon is the Earth's crust, while oceans and groundwater are secondary sources.
- Due to air circulation, the concentration of radon in the atmosphere remains low, but in indoor environments, it can reach significant levels (tens to hundreds of Bq·m⁻³).
- Radon decay products include heavy metals, which can attach to aerosols. When inhaled, these radioactive particles deposit on lung epithelium, increasing the risk of lung cancer.
Legal Regulations
The importance of radon exposure monitoring is recognized in regulatory frameworks, including:
- Act No. 87/2018 Coll. on Radiation Protection and amendments,
- Council Directive 2013/59/Euratom, which establishes basic safety standards for protection against ionizing radiation.
Metrological Support for Radon Measurement
Accurate radon activity measurement is critical for radiation exposure assessment and relies on direct measurement of radon concentration in different matrices.
According to Decree No. 161/2019 Coll. on Measuring Instruments and Metrological Control, instruments for measuring radon activity concentration (²²²Rn) in air and water and equivalent activity concentration in air are regulated measuring instruments and require annual verification.
Composition of the Secondary Standard for ²²²Rn Activity
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Radon Chamber (Figure 1)
- Storage unit for radon atmosphere with a volume of 1000 liters,
- Dimensions: 2 meters in length, 80 cm in width.
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Measurement System
- AlphaGUARD DF2000 (Saphymo, Bertin Instruments, Germany),
- Equipped with an integrated pump for flow mode measurement,
- Traceability to SÚJCHBO (Czech Republic).
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Gaseous ²²²Rn Source
- Activity: 100 kBq, Radon yield: 0.25 Bq·s⁻¹,
- Type: RF 100 (Secondary Standard, ČMI, Czech Republic),
- Dry-flow source containing ²²⁶Ra salt.
Applications
- Calibration and verification of radon activity measuring instruments,
- Environmental and occupational health monitoring,
- Regulatory compliance for indoor radon exposure control.
This secondary standard ensures accurate, traceable, and internationally comparable radon activity measurements, supporting both public health protection and scientific research.
