Contribution of airborne radon and thoron progeny to track density recorded by progeny deposition-based direct sensors

Radon and thoron progeny are natural radioactive elements that significantly contribute to the risk of lung cancer. Understanding their behavior in the atmosphere is crucial, leading to the development of both active and passive measurement devices. Among these devices, Direct Radon/Thoron Progeny Sensors (DRPS/DTPS) stand out, utilizing aluminized mylar-mounted Lr-115 detectors to measure the deposition of radon and thoron progeny. DRPS/DTPS have the capability to discriminate alpha particle energies based on different absorbent thicknesses. The Lr-115 detector possesses energy detection windows spanning from 0.8 MeV to 4.5 MeV, subject to variations based on etching and reading conditions. Consequently, the appropriate thickness of the absorbent in relation to Lr-115 proves essential for detecting alpha particles with sufficient energy to generate visible tracks on the detector's surface. While these sensors primarily detect alpha particles emitted from their immediate surface, there remains an un addressed question concerning their ability to detect alpha particles emitted from the surrounding air near the absorbent's surface—an issue of considerable significance. This study aimed to provide a comprehensive theoretical and experimental assessment of Lr-115 sensors, in conjunction with absorbents, and their capability to detect alpha particles emitted by airborne radon and thoron progeny. To achieve this objective, a simulation was conducted, and experimental procedures were implemented utilizing Lr-115 detectors coated with commercial foils equivalent in thickness to aluminized mylar. The results revealed a quantifiable contribution to the overall track density from alpha particles emitted from the surrounding air, impacting Lr-115 sensors designed for radon progeny (²¹⁴Po) and thoron progeny (²¹²Po) measurement. This finding underscores the importance of accounting for this previously unexplored factor in accurate radon and thoron progeny measurements, with implications for both research and public health. (author)