. -A1 a . . . ' LOFT -ORNLP 1098 1 4 . *** : : B. .. TEEEEEEE i 1 an 11:25 11:4 :46 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS -1963 ri Kanpo098 LOTE PO W . - i ON.THE Choice of a Fallout Shelter Protection Factor.. . Eugene P. Wienert and Everitt P. Blizard, a.ciuptong toimia that i. Oak Ridge National Laboratory** Oak Ridge, Tennessee : FUR PUBLIC RELEAO . T INTERESTE ON RECEIVING U :: V leiki PROCEDURE SECTION . . . . . . . . . . . .. :. . .. ini معضی هستند -- DE There is no unanimity concerning the appropriate magnitude for a fallout, s helter protection factor. Assuming a two-week sheltering period, and that the fallout arrives one hour after the explosion, the intensity of the radiation at the time to at which people emerge from the shelter 18 1000 times weaker than at the time of arrival of the fallout. This would suggest that the protection factor of a shelter be at least 1000 so that no one be exposed to more intense radiation in the shelter than he will be when he emerges therefrom. On the other hand, the decrease of the radiation intensity 18 very much slower two weeks after than it 18 two hours after the explosion. Hence, the total amount of radiation which one receives during the period from te to a very long time after the explosion decreases much more slowly with in- creasing to than does the instantaneous radiation intensity at time te. In fact, the total dose received from the time of emergence te to a very distant future decreases only as the fifth root of t, that is, it is proportional to t1/5. Hence, if one is in the open, the dose between one hour and two hours, and the dose after two weeks, are in the ratio of 2.18 to l. It can be argued that it makes little sense to reduce the former dose by more than a factor 10, because such a reduction suffices to render the early part of the dose to be only about 20% of the latter, apparently unavoidable, dose. This is received at a much lower rate, but lasts much longer, than the early radiation. The last consideration disregards, of course, several factors which mayi ...be of great practical importance. One of these is that the radiation 18, --, . iem.cdi . IN NUCLEAR SCIENCE ABSTRACTS RELEASED FOR ANNOUNCEMENT --- ......... .. ... - - . .. -- : -- - - - *Consultant. **Research sponsored by the U. S. Atomic Energy Commission under contract. with the Union Carbide Corporation. - - .... . :* . 1. .. vi . . . 5 Y . 11 . 1 - . . ** , - ' 21 - - . . - .. . * i * . ... La 1 - 1 ** l - . 1 - - . 1 ' $ . .. . . . me . . .. - . ." . after two weeks, in fact a thousand times weaker than originally. Hence the possibility of decontamination, by wasbing Away the fallout or by removing and covering up the upper part of the soil, are much greater than in the early period of intense radiation. Also, since a few hours' sojourn in the reduced radiation field after two weeks would not represent a major hazara, people could then be moved out of particularly heavily affected areas more easily than at the outset. Hence, if one succeeds in avoiding the early intense radiation, one will have a much better chance of coping with the later, weaker but much longer-lasting, residual radiation. This shows that it is well worth reducing the effects of the early radiation, by an adequate shelter protection factor, well below the 20% of the post-emergence radiation dose because this can also be reduced. After about two weeks the duse rate outside the shelter will have been reduced sufficiently to permit leaving the shelters periodically if not permanently. Thus it would be possible to accomplish some decontamination, whereby the fallout is removed or covered over to reduce the dose l'ate. For cities, where the surfaces are more or less impervious, the fallout can be washed down or swept up and removed, possibly in shielded containers or by trucks with shielded cabs. The radiation could be reduced by, about a factor 10 this way. For fallout in the countryside, decontamination would be more difficult, but turning over the surface layer and burying it to a depth of 12 cm should reduce the radiation intensity also by a factor of: about 10. Thus while possibilities of reducing the exposure to radiation after emergence will vary considerably with local circumstances, significant reduction factors may be expected to be achieved. We wish in addition to call attention to the fact that the biological damage 18 not proportion to the total dose received: It is smaller if the same total dose 18 received over an extended period so that the dose rate 18 + + . . . . 7 TOT ! ! . . . . . - .. . smaller. The reason therefor 1s that biological systems can recover to a . considerable degree from radiation injury. Hence, if a given dose 18 spread out over en extended period (of the order of a month or more for mammals), the organism will have largely recovered from the radiation received in the early parts of the period by the time a significant dose has been accumulated. Because of this phenomenon, the calculation of our first paragraph exaggerates the effect of the post-shelter radiation. The mechanism of recovery from radiation is not completely known and there is even some doubt as to its exact magnitude. However, the data available permit at least an approximate comparison of the effects to be expected, con- sidering recovery, from the extended period of weaker radiation after the sheltering period, with that from the short period of more intense radiation from which the shelter should protect. . The formula which expresses the variation with time, t, of the deleterious effect of radiation, as measured by the probability of short-term lethality, received at time t = 0, is usually quoted as -t/to da de + de (1) In this, d is the total damage at time t after receipt of one wit of radiation, 18 the permanent part of the damage, de la 90) 18 the reparable part thereof, and to 18 the recovery period, taken to be about 23 days or 550 hours. The functional form of (1) is uncertain, as are also the magnitudes of the constants occuring therein. However, (1) has been derived from experiments in the same general area in which it will be used. : The Intensity of radiation from fallout particles decreases proportionally fission to t-9/9 where t is the time elapsed since/took place. (It 18 the Integral of this intensity, from t to infinity, which 18 proportional to t. -1/5.) This . .: . Lii . o -- . times. less than sid aths and mile 18 quite accurate and has been adequately tested experimentally. The deviations therefrom are of the order of 20% for times. less than six months are in the direction to cause an overestimate of the dose received fox times beyond this. It follows from (1) and the t / rule that the total damage accumulated from exposure to fallout radiation during an interval which begins at time t, after the fission products were formed and lasts for a period T 18 ... . . proportional to det (a + det.+T-t)/t.. alte, T) = f (2) A It is convenient to measure all times in units of the recovery period. t. 23 days; thus if the exposure begins one hour after fission took place, then to a 1.550. Figure 1 shows the damage. accumulation with time in the early period, actually assuming that the fallout arrives 70 minutes after the explosion. The maximum damage occurs about 50 hours after that; for the radiation implied by the radiation intensity 1/t+o2 it amounts to 8.9 units if = 0.1 and dp = 0.9; 1t amounts to 8.8 units if full recovery (d = 0, 4, -1) 18 assumed. These are the numbers which will be reduced by the protection factor of the shelter. Even the damage during the early period 18 much smaller than it would be if no recovery took place: in this case it would approach, after a very long time, 17. 4 units. Figure 2 gives the damage, as a function of the time t after emerging from the shelter, for the cases in which this period begins at te - 0.5 (11.5 days), 1 (23 days), and 1.5 (34.5 days) recovery periods after the explosion. The three dashed curves give the damage calculated without taking the recovery into account. These continue to increase; their asymptotic values (for - 1 and du * 0) are indicated. One will note that these values decrease quite slowly . 1 1 - 2 -50 as functions of t, and constitute a large fraction of the damage 17.4 which one would receive without any shelter. "Che lower three curves give the damage assuming full recovery ( = 0, 4, = 1). The demage which corresponds to the commonly accepted case ( = 0.1, d. = 0.9) can be obtained by averaging the lower and corresponding upper curves of Fig. 2, with weights 0.9 and 0.1; respectively. The maximum damage 18 reached roughly one recovery unit after emergence from the shelter; it amounts to 0.69, 0.42, and 0.31 units for to = 0.5, 1, and 1.5. These are 13, 21, 29 times smaller than the damage without shelter. The ratio of maximm post-shelter damage to the no-shelter damage 18 plotted in Fig. 3 as function of the time te at which the people emerge from the shelters. The damage numbers of Figs. 1 and 2 apply for a radiation intensity of 1/+5 where t is measured in units of the recovery period t. This corresponds to 3.5 rad/hr at t = 1 hr; if the rate is, let us say, 100 rad/hr at 1 hr, the numbers of Figs. 1 and 2 must be multiplied by 100/3.5. If it were not possible to reduce the radiation dose in the post-shelter period by decontamination, evacuation, etc., the reasonable protection factors of shelters would be relatively small multiples of the numbers of Fig. 3, . 1.e., would be around the number 40 which constitutes the present minimum prc' ection factor of fallout shelters. Since, however, the post-shelter radiation dose can be decreased, a considerably higher protection factor is worthwhile and hence desirable. .. The principal uncertainty of the preceding calculation is whether the maximim damage in terms of increased probability in short-term lethality is the proper criterion for judging the undesirability of a certain radiation history. That this does not increase over the effect of an instantaneous dose of about 400 rad may be the relevant factor for immediate survival, but this ".. . . 7. :: 1 . 1 . 1 1 1 + . A * T 1 i . LE r . . + . is not the only relevant objective. Evidently, much more study on the various effects of a given radiation history 18 needed, and this would be of interest not only from the point of view of civil defense. . VI . J . . .** . 1 - . : . 1 MI . . : . L ..: . LT MTE, . . 7 ' 11 " . . : . . .. 11 . . t 2 . -k. .1 .. . .." . .. . ;?'.. . : 1 " . 1 ::: :'!! 7 . r - . ....*.*:: 1 . M . . . 7 . or instance, S. M. Michaelson and R. T. Odland, Radiation Researc! 16, 281 (1962) which gives also references to other literature. 1 , R . - 11.11 S .. . ! • 1 LEGAL NOTICE 2 . . . . - Bil.., ..-. T? This roport mu prepared u an nocount of Governmnat sponsored work. Helther the United Hatm, por the Comminion, nor any partou nothing a bohult of the Coraindham A, Makor my warranty or reprosatation, expressed or implied, wo muepost to the noor racy, completenoni, or sofalbouof the information contabood han to report, or that do we of the thing information, apparatus, metsd, or proowus dieloned to the report may not intentant privately owned rights; or B. derma uny Habilities with sent to the woof, or for dum m es from the un of tay lnformation, apparatus, wabod, or proon dioland to the reports , As und in the above, "persoa sothes on behalf of the Commission todo muy ployw or coatractor of the Commission, or employu ol make contrastor, to the home they such omployw or contrrotor of Commissionor employw at wel contractor prepared dienominates, or provides 10000 10, any buformation period to Mo employ out of contract with the Commission, or bla omployment with muola contractor. . 7. . 1 T . +. Y . . IT . . •:: ' . ^, . . 1. - .. . ... . . 2 LI . ---- :1 **" ' "'- . . .. UNCLASSIFIED · ORNL-DWG 64-11340 .. m any komponen . -• .• . ..o WITHOUT RECOVERY DAMAGE WITH FULL R ECOVERY :.' 0.05 0.10 ....0.15. .0.20...0.25 ; . . i . i. .. . . . .... .. . .. 'i' . 1. . * . . IL 1: Asin - : . ' 1 11 . T- .*** * . . :,!. ": . 1 . . '' . UNCLASSIFIED. ORNL-DWG 64-11338, . O - . .. YUV:.. :"" ... : *.-.-. 1 - . . - . I . . . te=0.5 :.:.! DAMAGE . . . = 1.5 I ---- WITHOUT RECOVERY WITH FULL RECOVERY - - - . -. - "" . · 0.5 . 1.0 1.3 UNCLASSIFIED QRNL-DWG 64-11339 *** WITH FULL RECOVERY REDUCTION OF MAXIMUM DAMAGE ACTUAL RECOVERY, . ...... 4.5 0.5 1.0 te, SHELTERING PERIOD . .pe .. . . for . . . . . END . .. . a. DATE FILMED 0/ 6 / 66 .