ne an Seas cae. ah et ee 592 : Gorpon MM. Dunyina Tance TI: Estrtareo Repuction in Gamma Doss Rates AT Tiree Feet AROVE THE GRoUND TO B& Expecrep Fro“ Various DECONTAMINATION Procepurnes on Lanp SurPaces* Procecure Ploviug (to depth of 8 inches) + Bulidozing or grading (to depth of 4 inches) Fj (clean dirt to depth of 6 inches) Seraping (to depth of 4 inches, with concurrent removal of exhumed dirt) Afproximete eduction 4 5 duction of radiation dose is the laase of 10 made accordingly;. it is not possible to establish beforehand any general rule of action based on radiologica! considerations clone. The complex factors entering into this problein cannot be discussed here. There is available, however, a considerable aniount of data on the radiological aspects of fallout to aid civil defense authorities in waking the decisions which will ultunately rest with them. The amount of protection afforded by ‘shielding is suggested in Table I. The exact dose rates that might be expected from a fallout cannot be predicted, but it appears reasonably certain that a shielding hee wane ted: . 6 ’ ~ “4 4ys aay tm * . . eenmpaeggiminnds Jag ‘ my oe : . oho , . A 2 Ryf factor of 1,000 would, even in the areas of . ft eee faa a “f gives reductions of contamination of sur- faces as estunated by one method of cieter- mination. (For more extensive anclyses sec references 12, 13, and 14.) * Based on data in Radiological Recovery of Fixed eras ground which might be accomplished by various operations on the soil. Table IV Factor Nilitary lpstallations (12). fa April 1958 The final factor of major benefit in re- fame, On the basis of radiological decay Tapié IV: Estraateo Repuction in CONTAMINATION OF SuRFacts Usinc a Fire Hosine ALETicb* Surface Concrete Wood Metal Roofing Approximate Reduction - Factor 10 . 0 30 30 * Based on a dry contaminant. For a slurry contatmiaant, the reduction factors might be only onethird a3 great. Pre-protection of wood aud conc:ete suriaces, ¢.g., wilh sealers or paints, mizht merease the reduction facter by a factor of about 3. (Based ou cata in Radislegical Recovery of Fixed Aciliiary Installations (12)). alone, the activity (disintegrations per minute) decreases approxiinately according to the principle of (time)~*. Thus, for every sevenfold lapse of time aiter a nuclear explosion, there will be a tenfold heavy fallout, reduce the radiation below reduction in dose rate. For example, if Jevels which might produce sickness. Such fallout occurs one hour after a detonation, a reduction might be attained by about 3 the dose rate will be one-tenthof its initial feet of earth or sand or 19 inches of con- value by the seventh hour; an additional crete. Even the cellar of a frame house tenfold reduction would require about two will reduce the dose rate by a2 factor of additional days of waiting. Si:milarly, the about 10, which might spell the difference total possible out-of-doors dose accumubetween relative safety and the danger in- lated from the first to sixth hour after detcident to full exposure. In the area of onation would be approximately the same maximum contamination, however, located as that from the sixth hour until one week within the 400 r ellipse of the fall- later. Further, this first-week dose would ot diagram, a factor of 10 might not be be about twice as great as the entire reenough to keep the accumulated dose be- maining dose possible for the lifetime of the low a hazardous level, even for a period of activity, even in the absence of weathering. half a day following fallout; in that case This rapid decay suggests the benefits of more protective shelters or evacuation protection in the early periods after fallout and, where possible, delay of entry would be required. The third measure that might be taken into a contaminated area. to reduce the radiation dose is decontaminaThe question is frequently asked as to tion of the environment after fallout has the time one must spend within a shelter occurred. Table III, based on field data or remain outside of a contaminated area. (12), indicates the degree of reduction in The answer depends upon a number of gamma dose rates at three feet above the parameters, such as the critera estabiished