Collection search - ADVISORY COMMITTEE ON RADIOLOGICAL PROTECTION: Letter: Dr. R.J.A. Lévesque to Drs. H.E. Duckworth and B.C. Lentle re thank you for your letter of Oct. 16 on subject of "de minimis". c.c.: P.E. Hamel, F.C. Boyd, R.J. Atchison and W.R. Bush