Indoor environment factor · measured in Bq/m³
Thoron (radon-220)
Part of: Radon
Also: Rn-220, radon-220
A short-lived isotope of radon released from thorium in soil and, notably, from building materials such as clay, earth and some gypsum. Its 56-second half-life means it comes from surfaces close by — walls rather than the ground — and it is often overlooked in radon surveys.
Why it matters indoors
Thoron decays too quickly to travel far, so concentrations fall steeply within a metre of the emitting wall; measurements near walls of earthen or clay-rich buildings can rival radon levels. Its decay products, however, are long-lived enough to accumulate and contribute to lung dose. Standard radon detectors either ignore it or are confused by it; thoron-specific or paired detectors are needed.
What the studies report
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| — | median 13 | residential occupants · dwelling | simultaneous radon (222Rn) and thoron (220Rn) measurements in 3,534 residential homes in 34 Canadian metropolitan areas covering 71 % of the population, 2007-2013; pooled log-normal analysis restricted to the 1,738 homes with thoron above the detection limit | F-0612 Chen Assessment of thoron contribution to indoor radon exposure i… (2022) | machine |
| — | other 4 | residential occupants · dwelling | simultaneous radon (222Rn) and thoron (220Rn) measurements in 3,534 residential homes in 34 Canadian metropolitan areas covering 71 % of the population, 2007-2013; pooled log-normal analysis restricted to the 1,738 homes with thoron above the detection limit | F-0613 Chen Assessment of thoron contribution to indoor radon exposure i… (2022) | machine |
| — | share-below 11 | residential occupants · dwelling | one-year measurement of radon and thoron with twin-cup track detectors in dwellings of Buddonithanda village near a proposed uranium mining site, Nalgonda district, Telangana, India | F-0647 Suman Radon and thoron levels in the dwellings of Buddonithanda: a… (2021) | machine |
| — | share-above 37 | residential occupants · dwelling | one-year measurement of radon and thoron with twin-cup track detectors in dwellings of Buddonithanda village near a proposed uranium mining site, Nalgonda district, Telangana, India | F-0649 Suman Radon and thoron levels in the dwellings of Buddonithanda: a… (2021) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
In the literature
- Assessment of thoron contribution to indoor radon exposure in Canada (2022). Radiation and environmental biophysics. doi:10.1007/s00411-021-00956-0 CKB 0436
- Omori et al. Impact of wind speed on response of diffusion-type radon-thoron detectors to thoron… (2020). International journal of environmental research and public health. doi:10.3390/ijerph17093178 CKB 0415
- Carlo et al. Thoron Interference on Performance of Continuous Radon Monitors: An Experimental Study on Four Devices and a Proposal of an Indirect Method to Estimate Thoron Concentration (2022). doi:10.3390/ijerph19042423 CKB 0448
Studies in the Coridum Knowledge Base in which this term is used. The definition follows standard usage in WHO, ISO and textbook sources; it is not quoted from these papers.
CKB = document number in the Coridum Knowledge Base, our curated library of peer-reviewed studies. Follow the DOI for the original paper.
Cite this page
Coridum Research. Thoron (radon-220). Coridum Knowledge G-0089, 16 September 2026. https://coridum.com/k/G-0089/