Well, here's the thing to remember: "background" varies from place to place. I used to live in Seattle, where the background was very low -- most of the local ground was glacially deposited mud and gravel, which itself was originally sedimentary in origin; the ground there is just less "hot" than some places. Now, I live in North Carolina, where I understand one of the reasons most houses don't have basements is that radon buildup is a real problem -- there's enough thorium in the bedrock and overlying clay to significantly raise the background here.

I'd bet I'm getting more "extra" radiation above the low background I've lived in for the past 20+ years from the soil than from the radioactive element in Super Takumar 1.4/50 -- and I can't put the ground in another room or get further away from it to attenuate the radiation.

In any case, 40% above average background is really, *really* not a big deal. You don't see a huge increase in cancers in the thorium belt on the eastern slopes of the Appalachians, where the background itself is 2-3 times what it is in Seattle (except where basements concentrate the radon exuded from the ground), after norming out lifestyle differences. Smoking is MUCH more dangerous, even than basements full of radon...