The draft document needs new supplementary information and revised conclusions in regard to Rn-220. A reference level including the exposure to Rn-220 should be proposed.
p 22 (21)…These typical (radon-220) values do not present radiological protection problems.
I can not agree with this statement considering e.g.
Shang, B. et al.. Thoron levels in traditional Chinese residential dwellings. Radiat. Environ. Biophys. 44, 193–199 (2005).
Sreenath Reddy, M. et al. Thoron levels in the dwellings of Hyderabad city, Andhra Pradesh, India. J. Environ. Radioact. 73, 21–28 (2004).
p 24 (25) Building materials…..However in the majority of cases this source of radon is of secondary importance compared with radon infiltration from the soil.
p 48 (136) …if building materials are controlled with regard to gamma-radiation, the radon exhalation is expected to be relatively low.
These statements are not true for Rn-220. Building material should be considered in more detail, e.g. traditional houses (clay) or multi-story houses (concrete contaminated e.g. with slag). Not only the radionuclide content is relevant, but the exhalation rate as well.
Chapter 2.2.2 should contain some paragraphs on Rn-220 measurement: in contrast to Rn-222, the indoor gas concentrations are highly inhomogeneous and progeny concentrations are more relevant for dose assessment.