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Thanks again to all of you who visited the Daghlian
website
(http://arnold_dion.tripod.com/Daghlian/) and I am especially grateful that some of you have expressed a desire to use it in your lecture courses. Recent discussion of criticality accidents have mainly concerned the blue glow phenomenon and its cause(s). Limiting the discussion to fatal accidents with an associated blue glow in Los Alamos, there are three documented incidents: Harry Daghlian, Jr. (August 21,1945), Louis Slotin (May 21, 1946) and Cecil Kelley (Dec. 30, 1958). The 1945 and 1946 accidents involved the same 6.2 kg plutonium core with tampers composed of WC bricks and hemispherical Be shells, respectively. The 1958 accident, by contrast, occurred when Kelley started a stir motor in a covered 225 gallon stainless steel tank (with a small viewing window) used for recovering plutonium from waste solutions. My interpretation of the accident reports, which are very incomplete, is that the blue glow occurred after an initial bright flash?? In an effort to explain the blue glow (1945-1946), Marshall Holloway (cf. Daghlian website) noted that a blue glow was associated with cyclotron beams, specifically a 20-microamp beam of 5-Mev deuterons in a darkened room. Also, Don Martin pointed out that 10 curies/sq. cm Po emits a blue glow, about 5 cm deep - the range of 5.3-Mev alphas. This phenomenon was directly demonstrated (June 6, 1946; 4 PM) with 5 curies Po/sq. cm on a sphere (total 18 curies) and with 1.5-2.0 curies/sq. cm (total 3 curies). Both required "lights out" and dark adaptation for the latter. (Note: The Daghlian and Kelley accidents occurred at night under artificial lighting; the Slotin accident happened mid- to late-afternoon, so the lab was lit with overhead lights and was partially sunlit.) More to the point, a rerun of the Daghlian accident was performed on October 2, 1945 by Aebersold, Frisch and Slotin. They were not able to see a blue glow in a darkened room in which 6 X 10E15 fissions occurred and the intensity of prompt gammas increased within "several seconds." I hope these these observations, as fragmentary as they are, are pertinent to recent postings. Arnold Dion (asdion@cyberenet.net) |