Be-7 measurement in an urban area using a low-resolution gamma spectrometer

Area of Science:

• Environmental Science
• Radiochemistry
• Geochemistry

Background:

• Beryllium-7 (Be-7) is a cosmogenic radioactive isotope produced by cosmic ray spallation in the atmosphere.
• Its distribution in urban soils and sediments is not well understood, limiting its use in environmental studies.
• Understanding Be-7 distribution is crucial for environmental monitoring and tracing pollutant transport.

Purpose of the Study:

• To quantify Beryllium-7 (Be-7) concentrations in urban soils and sediments.
• To investigate the influence of different urban scenarios on Be-7 distribution.
• To identify factors contributing to Be-7 accumulation in urban environments.

Main Methods:

• Samples of soil and sediment were collected from three distinct urban scenarios: a natural slope, a rainwater drainage ditch, and roadside sediments along asphalt curbs.
• Gamma spectrometry using a thallium-activated sodium iodide (NaI(Tl)) detector was employed for Be-7 activity measurements.
• No chemical separation was required for the analysis, simplifying the measurement process.

Main Results:

• Be-7 activities in soil samples from the natural slope and drainage ditch ranged from below the detection limit (5 Bq/kg) to 39±5 Bq/kg.
• Sediment samples from paved areas (roadside curbs) exhibited significantly higher Be-7 activities, reaching up to 873±5 Bq/kg.
• A clear contrast in Be-7 concentrations was observed between natural soil environments and accumulated urban sediments.

Conclusions:

• Urban roadside sediments accumulate significantly higher concentrations of Beryllium-7 (Be-7) compared to natural soil environments.
• Surface runoff during rainfall events is the probable mechanism for mobilizing and depositing Be-7 in roadside sediments.
• This study highlights the importance of considering urban runoff dynamics in understanding the distribution of cosmogenic isotopes like Be-7.