Thoron (220Rn) decay products removal in poorly ventilated environments using unipolar ionizers: Dosimetric implications

Ionizers are proven to be effective in reducing the activity concentration of radon/thoron decay products in workplace environments. However, limited studies have been conducted on understanding the mechanism of removal and the related size dependency. This study demonstrates the feasibility of reducing the activity concentrations in small chambers and in room environments up to a factor of about 7. Field experiments in an uncontrolled ventilation area such as a thorium oxalate storage shed have also shown promising results with a possible concentration reduction by a factor of 4. However, these reductions have been necessarily associated with an increase (3–5 times) in the unattached fraction of the decay products which is a significant contributor to the lung dose. Owing to this, aspersions have been cast on the capability of the ionizers in reducing the effective dose. An attempt has been made here to estimate the effective doses over a wide range of parameters such as the initial unattached fraction, activity reduction ratio and the change in the unattached fraction, which get altered due to the use of ionizers. The study proves that for realistically achievable activity reduction ratios of about 3–5 with the employment of ionizers, the inhalation dose in workplace environments can be reduced by a factor of at least 4, as indicated by model calculations.