Dr. Bernard Cohen has written extensively on radon, the LNT hypothesis and radiation hormesis in The American Journal of Roentgenology and elsewhere.
R Wilson M.D. Radiology ret.

http://www.phyast.pitt.edu/~blc/

I scanned his list, but did not download his 17 Mb "Catalog of Risks". Nothing in the other titles suggested natural gas as a source of radon.

There is no doubt that radon is a public health risk, but the source is structure (sometimes well water) and not natural gas used for cooking.

Alan