Measuring radon-222 in soil gas with high spatial and temporal resolution

Area of Science:

• Environmental Science
• Geophysics
• Analytical Chemistry

Background:

• Radon-222 (²²²Rn) is a naturally occurring tracer in soils.
• High spatial and temporal resolution is needed to measure soil gas radon isotopes without disturbing in situ conditions.
• Minimizing sample volume is crucial for improving measurement resolution.

Purpose of the Study:

• To develop and validate a method for sampling and measuring ²²²Rn in soil gas with high resolution.
• To enable the use of ²²²Rn as a tracer in soil studies.
• To provide an alternative to existing field-portable instruments.

Main Methods:

• Designed a soil gas probe with minimal dead volume (45 cm³ sample volume).
• Extracted ²²²Rn from soil gas samples into a scintillation cocktail.
• Measured ²²²Rn activity using a conventional liquid scintillation counter.

Main Results:

• Achieved a detection limit of 320 Bq m^-3 for ²²²Rn in soil gas with a 1-hour count.
• The method is suitable for typical soil gas ²²²Rn concentrations (2000-50,000 Bq m^-3).
• Demonstrated advantages in smaller sample volumes, speed, and reliability compared to field instruments.

Conclusions:

• The developed method allows for high-resolution soil gas sampling for ²²²Rn tracer studies.
• The primary limitation is the short 3.824-day half-life of ²²²Rn, requiring timely sample analysis.
• The method is not suitable for short-lived radon isotopes like ²²⁰Rn.