Ephant said:
I read 80% of Radon that can get into the house is from U-238 isotope. But how about Radon 223 (from U-235).
The proportions of Rn isotopes will depend on proportions of Th-232 and U-238 in the geological deposit, as well as the decay constants of various intermediaries and the respective Rn isotopes. Also, note that 'natural U' is about 0.72% U-235, although some deposits might be slightly greater.
The Rn from U-235 is Rn-219, with Ra-223 being the precursor. Actinium is a decay product in the U-235 decay series.
Rn from U-238 is Rn-222 and -218, the former having a short half-life (3.8 d) and the latter a very short half-life of 35 ms.
Rn from Th-232 is Rn-220 with a very short half-life of 55.6 s, the precursor being Ra-224.
Ref:
http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/radser.html
https://www.nndc.bnl.gov/nudat3/
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/isotopes-of-radon
"The average rate of production of
220Rn in the ground is about the same as that of
222Rn."
The articles emphasize
222Rn and the balance apparently being
220Rn. An article also mentions, "Radon accounts for up to 50% of the total internal dose from all natural background radiation sources and this, in turn, is due almost completely to two of its progeny, namely, polonium-218 and polonium-214, which decay via the release of
α-particles.
Alpha particles, while lodged in the airways of the lung can damage the cells lining the airways, thus inducing lung cancer." The
218Po and
214Po are decay products from the
238U decay series with precursor
222Rn.
With respect to "But how about Radon 223 (from U-235),"
223Ra is a precursor to
219Rn;
223Ra is solid so should be in the vicinity of it's production unless it or a precursor is dissolved in groundwater.