Correction for radon distribution in solid/liquid and air phases in gamma-ray spectrometry

The effect of radon diffusion and distribution between a 226Ra matrix and the top air gap inside sample containers for gamma-ray spectrometry was studied. Containers filled at almost 100% or just 70% of total capacity yielded correction factors of about 7% and 20% respectively. Applying these correction factors allowed activity values calculated from 226Ra or radon decay products to agree within 2%.

► Secular equilibrium is required for 226Ra gamma spectrometry based on radon decay products.
► If an air gap is present, change in geometry for radon products occurs due to radon diffusion.
► A model was developed and validated to take into account this effect.
► Efficiency transfer methods were applied for sample holders filled at 100% or 70% of total capacity.
► Correction factors were about 7% and 20%.