Correcting for H₂O interference using a RAD7 electrostatic collection-based silicon detector

Area of Science:

• Environmental Science
• Nuclear Physics
• Analytical Chemistry

Background:

• Radon monitoring is crucial for assessing environmental and health risks.
• Silicon detectors are used for electrostatic collection of polonium ions, but their efficiency can be affected by environmental factors.
• Understanding the influence of water molecules on ion collection is essential for accurate radon measurements.

Purpose of the Study:

• To investigate the effect of water molecules on the electrostatic collection efficiency of polonium-218 ions onto silicon detectors.
• To compare the performance of silicon detectors with a humidity-insensitive scintillation cell under varying humidity conditions.
• To develop correction factors for soil radon readings affected by humidity and desiccant use.

Main Methods:

• Utilized a radon monitor (RAD7) connected to a stainless steel chamber with both a silicon detector and a ZnS scintillation cell.
• Manipulated water molecule concentration in the chamber by using desiccants or bubbling water.
• Measured the relative efficiency of the silicon detector against the scintillation cell across a range of water content (0.00075 to 0.014 g).

Main Results:

• Silicon detector efficiency decreased with increasing water molecules, indicating a negative impact of humidity.
• The humidity effect was more pronounced during humidification than drying, attributed to cluster formation of polonium ions.
• Temperature (18.5-35.6 °C) did not significantly affect detector efficiency.
• A humidity-dependent error range of 1.8% to 7.5% was observed.

Conclusions:

• Water molecules significantly impair the electrostatic collection efficiency of silicon detectors for polonium-218 ions.
• Developed correction factors are necessary for accurate soil radon measurements, especially after desiccant removal following potential Non-Aqueous Phase Liquids (NAPLs) leakage.
• The findings are critical for improving the reliability of radon detection systems in diverse environmental conditions.