Looking forward to the results of Thomas's discourse with Pam Mosier-Boss and the discussion of similar papers. My question would be if the phenomena could be attributed to 'background noise' i.e. radon, then what controls were there to eliminate this?
Good controls and enough runs can eliminate this kind of question. Mosier-Boss et al. rule out air-borne radiation. Also, they use an americium standard on the corner of each chip in order to have something to compare against.