operation sandstone. nuclear explosions 1948, scientific director's report of atomic weapon tests

8/9/2019 Operation Sandstone. Nuclear Explosions 1948, Scientific Director's Report of Atomic Weapon Tests

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FROM:Distribution authorized to U.S. Gov't.agencies and their contractors;Administrative/Operational Use; 01 JAN1949. Other requests shal l be referred toAir Force Special Weapons Center, KirtlandAFB, NM.

AUTHORITY6 Nov 1957 AFSWC, per document marking; 9Oct 1958 AFSWC

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AUTHORITY31 Jan 1952 DoDD 5200.10

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OPERATIrON SANDSTONENUCLEAR. EXPLOSIONS

1948

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BEST AVALABLE COJPYApproved lo., pu:K

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SCZITIIC DW1MTaRIS RIMJTC' ATOMIC WEA.P TESTS

AT ZWIl3TCK, L94

Amex 9

f ~CO!ITANINTIC9 STUDIISPart I

RZ5IDKUL CONTANIMlTICt N miH RAMS

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Task Group 7.6 - Project Report

R!SIDUAL CONTAMINATION IN THE CRATERS

OPERATION SANDSTONE

byCiM. H. L. Andrews, USPHS

Rt. L.N9rph

1 Januar7 1%9 rojrot, 7.1-17/38-3


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TABLE OF CONTNITS

PageABSTRACT . ................ . 3

OBJETIVE .................. . . . . . 6

HISTORICAL .................. 7RESUPLMTAL ........... ....... . . . . 8

1. X-ray Crater . .. .. .... ... 12

2. Yoke Crater . . . . . . . . . . . . . . 223. Zebra Crater . . . . . . . . . . . 244. Alpha Measurements . .......... 24

DISCUSSION AND CONCLUSIONS . . . . . . . .*. . 26

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ABSTRACT

Residual contamination in the crater was measured af-te r each of X-ray, Yoke, an d Zebra explosions, A sampletaken about 100 feet from each tower base was followed fordecay using a Geiger-Muller counter an d when sufficientlyreduced in radioactivity to permit handling, the specificactivity of the sample was determined. In addition to thecrater samples, material from the skin of drone aircraft,collected by use of scotch tape, were examined after testsYoke and Zebra.

For test X-ray, at about H plus 7-1/2 days, a cratersurvey was made extending along the Hartman line from 100feet to 1200 feet from the base of the tower, measurementsbeing taken at 100-foot intervals. At each station the ra-dioactivity of soil samples was determined at one-inch, two-inch and four-inch-depths. Gamma radiation above the sur-face was determined with an ion chamber survey instrument.

Decay curves did not fit the expected curve fo r a Mix-ture of fission products and Na24 but indicated that per-haps some other activity, not identified, wa s present.Fractionation of the fission products is another possibleexplanation. The best fit was obtained with t-1-45 for thefission products but this was outside of any probable value

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fo r this time period. At all distances studied the sam-ples from two inches and four inches below the surface showednearly pure fission product activity. Neutron induced ac-tivities were observed in concrete and steel at about 1000feet from the tower base.

For test Yoke, at about H plus 57 hours, a crater sur-vey was made extending from 1200 to 4500 feet from the tow-er base, and decay curves were taken of the samples. Sam-ples were removed from the drone planes at about H plus 7hours and decay curves were run. The drone plane decaycurves are substantially different from the crater decaycurves, probably because the ratio of fission products toactivated surface material in the cloud was different fromthat in the dirt samples. As in test X-ray, the decaycurves indicated a mixture of fission products, Na2 andperhaps some unidentified activity. Since all samples fortest Yoke were taken at greater distances than fo r testX-ray, direct comparison is not possible.

For test Zebra, as in test Yoke, crater decay curvesand drone plane decay curves did not agree. Again these in.-dicated a mixture of fission products, Na24 and unidentifiedactivity. No crater sampling survey was made.

It is concluded that failure of samples to follow theexpected curve is perhaps due to large amounts of activity

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induced in unknown elments with fractionation another pos-sible explanation. Because of the atypical nature of thesurface, the data are not very useful fo r predicting theradiological hasards following air bursts.

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OBJBCTIV

Heasurements in connection with this project were madefo r the purpose of obtaining as complete information aspossible about the radiation hazards existing in a laud a-rea which had been exposed to an air burst atomic bomb.They were designed to be useful in planning operations inthe future as wel as during OPEATION SANDSTOZ i tself.With reasonably good data obtained as soon as possible af-ter the burst it is considered possible to extrapolate backso that the hazards existing very soon after burst can bedetermined.

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HISTORICAL

Following the test at Alamagordo, measurements weremade of radioactive material from the crater. These meas-urements were made primarily fo r determining the perform-ance of the weapon and were not completely satisfactory forestimating the rad'ation hazards existing in the crater.The decay curves indicated the activity fell off accordingto t-1, 2 . At Bikini measurements indicated that most ofthe residual contamination following the air burst was dueto the neutron induced activity in the sodium of the seawater. In the underwater explosion at Bikini most of theactivity resulted from fission products and the decay ratefollowed a t-l' 3 1 aw. It was hoped that the present projectwould provide more complete information on the radioactivesituation existing after an air burst bomb.

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EPMIMNTAL

As soon as possible after each detonation, which inpractice turned out to be about H plus 7-1/2 hours, a sam-ple of crater material collected from a point about 100feet from the tower base was delivered to TaEk GroLap 7.6on the USS BAIROKO. Aliqaots of this sample were finelyground with a mortar and pestle and thin layers of this ma-terial were put into sample cups fo r measurement. The spe-cific activity of this material as received was so highthat original samples could not be weighed. Specific ac-tivities were determined from later measurements made onsamples large enough for accurate weighing.

One sample was run using a thin window beta sensitivecounter having a window of about 2.0 mg. Der cm.2 equiva-

lent thickness, and a second sample cup was run using athick wall gamma sensitive counter with an equivalent wallthickness of about 200 mg./cm. 2 . These counter tubes wereconnected to General Aadio Company type 1500-A countingrate meters which in turn were connected to Esterline-Anguscontinuous chart recorders. Th e sizes of the initial sam-ples were adjusted so that a counting rate of aporoximately18,000 counts per minute was obtained. After the sampleshad decayed so that only about 600 counts per minute wereobtained, the samples were replaced with larger ones tobring the counting rate back to about 18,000 per minute.

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After the initial rapid decay had taken place somue ofthe samples were transferred to counter tubes connected totype 161-G scaling circuits of the Instrument DevelopmentLaboratories. Counts were taken on these scaling circuitsat appropriate intervals and, wherever possible, the sam-ples were left in position between measurements. This wasnot always possible because the analytical requireut.1ts in-cidental to radiation health protection required the use ofscaling circuits on several occasions.

In addition to the crater samples described in theforegoing paragraphs, scotch tape samples, taken from thedrone airplanes, were run on tests Yoke and Zebra. Thesesamples were obtained by applying a niece of scotch taneto the leading edge of the wing of a drone plane known tobe contaminated and then stripping the scotch tape andsending it to the laboratory fo r analysis. In the labora-tory a small portion of the tape was placed in a samplecup with the sticky side up so that the beta measurementwould not be affected by the absorption of the scotch tapebacking.

All of the counting equipment used in these measure-ments had been carefully calibrated before the measurementswere started and calibrations were repeated at frequent in-tervals throughout the run. Beta calibrations were made

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using standard samples of radium D plus E, making use ofthe 1.17 Mev beta particles from radium L. Gamma-ray cali-brations were made using Co60 secondary standards which hadbeen checked against Co6 0 standards furnished by the Nation-al Bureau of Standards. Frequent determinations were madeof the resolving time of the GM counters and all data ob-tained from the records were corrected for this resolvingtime. All the samples had a sufficiently high specific ac-tivity so that very thin samples could be used, and none ofthe results were corrected fo r self absorption.

On X-ray plus 7 days a crater survey was made extend-ing along the Hartman line from 1200 feet to 100 feet fromthe base of the tower. Readings were taken at stations at100-foot intervals; the 400-foot distance was omitted be-cause of over-exposure to radiation. At each station soilsamples were obtained by driving into the ground a sharp-ened piece of aluminum tubing to a depth of about 6 inches.When this tubing was removed it contained a core sampleof soil down to a depth of about 4 inches. These werecarefully wrapped to prevent loss of material and were tak-en aboard the USS BAIROKO fo r analysis. At each stationgamma intensity measurements were made with an ion chambersurvey instrument held about 3 feet from the ground. Theintensities given in this report are averages of readings

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taken over a radius of about 10 feet from the station. Inaddition, surface samples were taken at each ,tation bycarefully scraping up the top layer, not over 1/16 of aninch deep, from an area close to the station which had ob-viously not been disturbed since the blast.

In the laboratory these samples were prepared fo r a-nalysis by grinding, and decay curves were run in the sameway as fo r the crater samples described in the foregoingparagraph. Samples from the aluminum tubing were obtainedby drilling holes through the tubing at distances of 1 inch,2 inches, and 4 inches below the surface of the soil sam-ples inside the tube. Through these holes small sampleswere extracted fo r analysis. In addition to the foregoingdescribed measurements, measurements were made on surfacesamples brought in at irregular intervals by the monitoringgroup.

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RESULTS

1. X-ray CraterFigures 1 to 4 show the decay curves obtained from

the crater samples collected at about H plus 4 hours. Aninspection of these curves, particularly the log-log plots,shows that the decay is fa r from the t" 1 "2 law expected forfission products. From the semilog plots it is evident thata large fraction of the activity was due to 14.8 hour Na24produced by the Na2 3 (n, 1) Na24 reaction.

Attempts were made to fit the observed decay curveswith an equation of the typeA = K" -Xt plus L Mi

t1. 2where A = observed activity (counts per minute)

A= decay constant of Na24 = O.0468/hourt time in hours

K and L = constants

The first term in Eq. (1) gives the contribution of Na24to the total activity, and the second is the fission pro-duct contribution. By choosing two points on the observeddecay curve the two constants can be evaluated.

When this process was carried out it was found thatthe decay predicted by Eq . (1) did not fit the observed de-cay curves. The fit depended on the points chosen fo r th edetermination of K and L and by a suitable choice a

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reasonably good fit could be obtained at either short orlong times, but not at both. It appeared certain that thesample contained some other induced constituent which wasdecaying with a half-life considerably longer than that ofNa24 or that fractionation of the fission products had oc-curred, thereby changing the second term of Eq. (1).

In an attempt to determine other constituents Eq . (1)was extended by adding terms of the type

and using values fo r X' appropriate to constituents whichmight have been present in appreciable quantities. Amongthe isotopes suspected and tried were

14.3 day p32 from p31 (n , ' or S32 (n,p)8.5 day Ca4 l from Ca40 (n , 2n)12.4 hour K42 from K41 (n, 9)

18 0 day Ca4 5 from Ca44 (n, V)No consideration wa s given to s35 from C1 (n,p) because thesoft beta emission unaccompanied by gammas would have beendetected with very low efficiency by the beta counters andwould have produced no response in the gamma counters.

Even with tw o additional exponential terms in Eq. (1)there was little improvement in the fit beyond that expected

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from the fact that more points were forced to coincide inthe determination of the constant terms. Th e lack of fitis beyond the experimental error, but at the present timeit is not known what elements are producing the deviationfrom the expected curve. Longer term measurements mayserve to identify them.

Some attempts were made to obtain a better fit by ad-justing the exponent of t in the fission product term.These attempts were not successful. It may be noted thatthe beet fit was obtained with t-1 .45 but this is outsideof any probable value and undoubtedly represents a compen-sation fo r the unknown elements or fo r the possible frac-tionation.

The results of the crater survey of X-ray Plus 7 daysare shown in Figures 5 to 10. It should be noted that inFigures 5 to 10 the relative heights of the curves are with-out significance. The large spread in the values of specif-ic activity did not permit a ready comparison of decays, sothe heights in Figures 5 to 10 were adjusted arbitrarily.The slopes of the various curves were not changed by the ad-justment and may be compared directly.

A comparison of these curves with the expected t-1.2fission product decay shows that at all distances studiedthe samples from 2" and 41 below the surface show nearly

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pure fission product activity. The samples taken fromnearer the surface show a decay corresponding to variousmixtures of fission products and other constituents. Thefact that surface samples did not follow the expected t-1.2fission product decay while samples at 2" and 4" below thesurface did follow the expected decay is strong evidence a-gainst fractionation and for the formation of unidentifiedinduced activities. Fractionation, however, is still be-lieved to be a possibility.

To calculate the percentage activity due to fissionproducts the assumption was made that the only other activeconstituent was Na2 4 . This is not true, but the error isnot great and is probably less than the sampling error re-sulting from the use of data from the small samples whichwere taken. Table I shows the percentage of fission pro-ducts calculated in this way at H plus 186 hours, the timeat which measurements were begun.

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Table I

Percent F, P. at 186 HoursA B C D

Depth 0 li" 2" 41

Distance 100 ft. 46 100 100 10020 0 ft. 48 69 100 1003OOft. 42 42 100 100500 ft. 44 100 100 --600 ft. 32 100 -...700 ft. 37 100 100 -800 ft. 35 100 100 100900 ft. 44 47 100 10 0

1000 ft. 36 36 100 1001100 ft. 98 100 100 1001200 ft. 100 100 100 100

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The results shown in Table I are somewhat surprising.In view of the penetrating power of neutrons it is diffi-cult to explain the low values of induced activity shownby the one inch samples, and the absence of induced activi-ty at greater depths. Th e presence of fission products inthe lower samples is explained by assuming that the fissionproducts settled out on the surface and were carried downinto the soil by subsequent rains. Neutron-induced iso-topes will be produced throughout the entire volume re-ceiving the neutrons and hence will not be washed down byrain.

Equally surprising is the absence of induced activityin the surface sample at 1200 ft. Measurements made on avariety of samples taken from-above the ground surfaceshow that there was a substantial neutron flux at 1200 ft.The original surface material with the induced activitymay have been carried away in the bomb cloud.

Th e total specific activities as calculated from thebeta measurements are listed in Table I.

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i-The data of Table II are plotted in Figure 11 together

with the readings of an ionization chamber survey meter.It will be noted that there are two "hot soots" at 700 ft.and 1000 ft. respectively. These "hot spots" appear onlyin the surface samples and are not evident in either thesub-surface samples or the survey meter readings. The sur-vey meter readings show a maximum at 800 ft. which ma y bedue to the gamma radiation from the two "hot spots".

The total residual fission products left in the craterwere estimated by the following procedure: Each radioac-tive assay was assumed to be representative of an annularvolume extending to equal distances from the samplingpoint. Thus the 800 ft. surface sample was assumed to rep-resent the conditions in a ring of radii 750 and 850 ft.to a depth of 1/2", and the 900 ft. 2" sa&-ple, the condi-tions in a ring of radii 850 and 950 ft. from depths of1-1/2" to 3" . The specific activity of the sample was mul-tiplied by the total mass of sand in the appropriate vol-ume, assuming a density of 2.0. This activity was correct-ed by applying the proper percent fission product obtainedfrom the decay curves so that the contribution of Na2 wasexcluded. The results were then corrected by the t"1"2law to H plus on e hour. No calculations were made for thecontribution beyond a radius of 1250 ft. This probably

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introduces very little error because the specific activi-ties at 1100 and 1200 ft. are low.

The values found by this calculation are:Total fission products in crater at 7H plus one hour 2.3 x 10 curies.Total fission products in crater atH plus 186 hours 6.4 x 104 curies.The sampling errors in this estimate are undoubtedly largebut this method appeared to be the only way of approximat-ing the figure from the data at hand. Since these valuesare only a small fraction of the total fission productsresulting from the explosion it may be concluded that mostof the active material was carried away in the cloud.

Lack of facilities prevented a comprehensive study ofbeta and gamma energies. One gamma absorption curve wasrun at H plus 15 hours with the results shown in .Figure 12.Th e absorption curve is characteristic of a monoenergeticgamma ray with a half-value thi*.ness of 1.13 cm. of lead.This half-value layer corresponds to a photon of 1.3 Mevenergy. Th e activity of the sample at H plus 15 hours wasapproximately 75% Na24 and 25% fission products. The pho-ton energy observed agrees as well as can be expected withthe 1.38 Mev gamma ray from Na2'. The 2.76-Mev gamma rayemitted in cascade with the l.4-Mev photon was not observed,probably because of a lower counter efficiency for the

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higher energy and because the lead absorption coefficientsfor the two energies are not greatly different.

Some of the random samples measured are of interestparticularly in connection with the low induced activityfound in the soil samples at 1000 ft. On H plus two daysa sample of the cement from the O.C.E. structure at 1000 ft.was carefully removed. The sample was taken from the in-terior of the proximal wall and care was exercised to pre-vent its contamination with residual active proAucts. Th ebeta decay curve on a finely powdered aliquot of this sam-ple is shown in Figure 13 . Most of the activity is due toNa24 induced by neutrons. The specific activity of thesample at H,plus 22 hours was 2.8 x 10-4 microcuries permilligram. Since the original sodium content of the ce-ment is unknown this figure cannot be used to determinethe neutron flux.

Neutron induced activities were also observed frCEsamples taken from the interior of iron stakes driven in-to the ground just in front of the 1000 ft. O.C.E. struc-ture. Th e samples studied were about 3" above the groundlevel at the time of the blast. The decay curve, Figure14, is complex and has not been analyzed into its compo-nents. Th e specific activity at plus 130 hours was4.8 x 10"3 microcuries per milligram.

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The cement sample from the 1000 ft. O.C.S. structureappears to differ in activity from a sample taken from th ebase of zero tower. The first measurements oi. the lattersample curve were made at H plus 272 hours and unfortunatelymeasurements on the other samples were terminated at aboutH plus 150 hours so they are not directly comparable. AsFigure 15 indicates the tower base sample shows an activity4ith a half-life of at least 19 days with shorter-lived com-ponents.

2, Yoke CraterMeasurements were started on the Yoke crater sample at

about H plus 9 hours and on the scotch tape samples from thedrone planes at H plus 7 hours. The decay curves are shownin Figures 16 to 23. As in the previous test the crater de-ca l curves indicate a mixture of Na24 and fission products.Ot)ier active materials may be present fo r observed curves can-not be fitted with a two-constant equation having terms forNa2 4 and fission products.

The decay curves fo r the drone plane samples are sub-stantially different from the curves from the crater samples.The differences cannot be attributed to fractionation butare probably due to differences in the amounts of surfacematerial picked up and carried into the cloud along with th efission products.

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Lack of time prevented a crater survey comparable tothe one carried out fo r the X-ray crater. On Yoke plus 3days a series of surface samples was collected along a radi-al line from the Yoke tower. The specific activities asmeasured at H plus 57 hours are given in Table III.

Table IIIDistance ft. rnicrocuries/miL

1200 0.0831500 6.6 x 10-61800 1.9 x 10-62100 7.0 x 10-72700 1.4 x 10-63000 4.8 x 10o-3300 4.6 x 10-83600 5.8 x IC-53900 1.7 x 10-84200 1.0 x 1094500 1.2 x 10-8

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The samples were all taken from greater distances thanin the X-ray crater survey and so direct comparison is notpossible. Th e data seem to indicate, however, that at a-bout 1200 ft. the contamination drops sharply to relative-ly low values. This is not inconsistent with the findingsfor the X-ray crater.

3. Zebra CraterTh e decay curves fo r the 2 samples are shown in

Figures 24 to 31. Once again the curves show a mixture ofNa2 4 and fissi~n products together with unidentified com-ponents. The decay of the drone samples does not agreewith the decay of the crater samples. Here again the lackof agreement is probably due to the pickup from the sur-face of variable amounts of contamination or to fractiona-tion of the fission products. No crater sampling surveywas made so there is no data corresponding to that obtainedfrom X-ray and Yoke.

4. Alpha MeasurementsSome alpha particle measurements were made using

Eastman nuclear particle emulsions and a Simpson propor-tional counter. Alpha particle tracks were identified inthe photographic emulsion but quantitation was made dif-ficult by the background fog produced by the high beta andgamma activity. Quantitative results from the track

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counts did not check with the re-ults from the proportionalcounter and no satisfactory explanation for this discrep-ancy has been found.

Alpha activity in all samples was low so that longcounting times were required to obtain significant results.Values of beta/alpha ratios on soil samples were about 105at plus 72 hours fo r both X-ray and Yoke tests. This cor-responds to a plutonium content of about lo-3 microgramsper gram of soil but this figure is not accurate beyond or-der of magnitude.

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DISCUSSION AND CONCLUSIONS

The outstanding result of all of the decay curves isthe failure to find components corresponding to the t-1.2law to be anticipated fo r fission products. This is dueto the large amounts of induced activities observed or tofractionation. The amounts of these activities variedfrom sample to sample and contained unidentified isotopesso that a separation of the composite decay curve was notobtained. It is probable that with long-continued runssuch a separation could be obtained. The value of suchan analysis, however, is rather doubtful.

All of the craters were atypical in that detonationsover soil of the type encountered are not to be expected.For this reason a large scale continuation of the decaycurves seems unwarranted. Some measurements are beingcontinued on one sample from each crater.

No clearcut evidence of fractionation was obtainedbecause of the large and variable amount of induced activi-ty ,

Because of the atypical nature of the surface the da-ta obtained are not very useful in predicting the radio-logical hazards following an air burst. It is hoped thatsubsequent tests may be held over more typical terrain sothat a complete analysis can be obtained.

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pi 4GAMMA DECAYX CRATERFIG. I -I VT

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1 310 X--SH R TI 'De A?--"4Z(u E I EFT HAND SCA

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a. a"BEOURFACE -=- D x4" "" -

0 100 200 30 0 400 500 60 0 70 0HOURS AFTER DETONATION

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vai- r -- X GRATER D

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HOURS AFTER DETONATION

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V

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-X GRATER DECAY7,__100) FEET>t---, ILE:. FIG.9 7

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LEDSHEETSF ABSORBERFIG82


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HOURS INTERIO C.0A~0FRO ZER TOERB


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HOURS~FTRAETNAIOFIG26


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HOURS FEDETNTON

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4 +t + tTTMTlL10 .1 110 2 3 4 5 6 7 a 9ib 4 " 160 3 4 it;boHOURS AFTER DETONATION

46


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:- ;YOKE CRATER;...

i 1 4 H-,.i A t.V

' S 6HOURS 7JAFTE DETNAIO- 47T


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105, +WV4++H4HfHf4-+ 144++H++H+ F+ ! i I4i-iF++-j4 1- ' litI-H 4 -4m. :,:F- IX: T! A QECAF,...... ... MOYOKF NF

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HOURS AFTER DETONATION

48 -


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- - -BETADECAY- ''DRONJ1 _ FI. 23:

-1--7 7

tt 4+41

LO ~ ~ H 1 -1 T, J?8HOUR ATERDTNTO444.


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10

GAMMA QECAYI I T I I I I I F IG. 24

104,

I I I T I

.110

TIT,

7 T4-4-

210 2-80 40 so 120 160 200 240 280HOURS AFTER DETONATION

50


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SHORT TIME DECAY- ;-

1000 12 4

HOURS ATIER DETOATO

Ti5ll


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10

~ G'AMMA DECAY

HOURFER DTONTIO- 52IG.


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-----------. . . . . . . . . .

BETA DECAYz F1

1104 SH -RT TIME DECAY....

... ............

... . .......

tun)

10 ME DECAY...............

I I T

I ab 0 20 4- so so 100 120 --- 1400 100 200 300 400 500 600 700HOURS AFTER DETONATION

53


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5, .I.....TE

1 ....... 00HOURSAAMDTREETNAYO

B R4E


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105-- Fr" 14 BETA DECtt Z E B RA GRATEW

. .... ... ...

.. .... It

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IT' I"

10 LL6 2 3 4 5 6 1 a 2 3 4 5 6 '160 2 3 4 & 6 7 OboHOURS AFTER DETONATION

55


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5to7GAMMA DECAY:w ; p ZEBRA DRO-NE:

FIG. 30:7- 1'1'.:ITI I

410 FI, 44 - 7A 2.0pTIT ..... up

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t4 1.32iT:;V TEll102 Ei i t3 4 s 6 7a lb 2 3 4 5 1 1 fdo 2 3 b 6 WboHOURS AFTER DETONATION

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105, i 1 1 1 t H++41111 1,41+ -4+ 1; 4" f1144- i- 7r T. ,,,,BETA DECAY,

7, 1 1 ::zj.-' I p A"L::: z

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110 1 IV I 4-H1: Iffi2 s 4 11 6 7 a 90 0 2 4 6 6 1 a 100 2 s 4 6 6 r 0 WooHOURS AFTER DETONATION

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SCJUTIFIC DUM.TIMS' RIPMTCr &TOMC, IRFPOM TE~ST

&T ZlIwmvm., 19/4.

AD1ms1 9

CONTAMIW~foN STUD=~

par L 11

AIR SURVI~! M?&OMU GOOIAjMITIWf


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Task Group 7.6 -PrOJ*Ot RePort0-47 Radiological ROhLusisseflov Siurw'Y

AIR SURVE OF GROUND CONTAMINATION

I OpERATIO1N SANDSTONE

by*LCDR Be e KING* (M) Ss

projgot ofrioer

30 June 1948 Proeoot ?.1-17/RS(DL)-4


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TABLX OF COEBITUSpage

ABSTRACT 2OBJCTIVI 3HISTORICAL 3

Materials and lquimonnt 5Calibratiou Procedures 6Decay 7Surface Measurements a

OpsRATION8 9Phase I 11

Phase 3 12RMSULTS 13

Test X-ray 16Test Yoke 20Test Zebra 25

INSTRUVENT TZSTS 27DISCUS810N 31

Maximm Intensity at oach Altitude 31Boundaries of the Radiation Field Abowe the Crater 33Intensity of Radiation Field Abowe Crater 35

ttenuat ion 36-1-


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TABLE OF CONTENTS (continued)Page

Mrial Survey of Fall-Out Areas 37CONCLUSIONS AND RECOMMENDATIONS 38REFERENCES 40

APPENDIX I - Test X-ray - Charts and GraphsAPPENDIX 2 - Test Yoke - Charts and GraphsAPPENDIX 5 - Test Zebra - Charts and GraphsAPPENDIX 4 - Air Radiologioal Survey in Helicopter,

Type HOS3, Zebra Plus Four DaysAPPENDIX 5 - A Oorrelation Between Aerial Survey

Data and Ground Survey Data, byT. N. White, MD

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ABSTRACT

Air radiological surveys were conducted with a C-47airplane on eight occasions during the three atomic weapons'tests at OPERAION SANDSTONE* A single survey at low

* Ialtitudes was also conducted with a Type HOS helicopterfollowing the third test. These surveys provided informa-tion which could be used to estimate intensities of sur-face contamination and to measure the extent of the radia-tion field above the crater* It was observed that theradiation at 1,000 feet was approximately 1/120 of theaverage intensity in the orator itself* Crater activitiesestimated by means of this factor and an average intensitymeasured at 1,000 feet might have been in error by asmuch as a factor of two. The maximum altitude at whichradiation could be detected a few hours after each testwas 7,000 feet. The results obtained from these surveysare considered -to be of sufficient accuracy to warrantcontinued analysis. Preliminary work has indicated thatthe orator aots as a point source for altitudes greaterthan 1,000 to 2,000 feet. Various types of existing fieldsurvey instruments were tested and a number of improvementsare reoommended. The over-all results of the project indi-cate that the aerial survey shows promise as a possiblemethod of measuring the approximate extent of a oontaminatedarea in the event of atomic warfares

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OBJWCTIVB

The objeotive of this projeot is threefold, (1) toprovide an serial reoonnaissanoe survey fo r the determina-tion of intensities of gaia radiations within the blastarea without exposing personnel to harmful intensities ofradiations suoh as would be encountered in surface opera-tions; (2) to aooumalate data fo r oonfirmation of theoret-ioal caloulations regarding the attenuation of ganma radi-ation above large land and sea area bouroes3 and (3) totest instruments which would be practical for use in aerialsurveys of oontaminated areas in the event of atomic war-fare*

HISTORICL

The first aerial survey of a land area exposed to anatomic bomb explosion was made at the Trinity site approx-imately one year after that test had been conducted. Thissurvey was made in a small single engine airplane. Thedelay from the date of th e test to the date of th e surveysomewhat limited its praotical value, but it pointed out

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the possibilities of this type of operation (i)*. Aotiv-ity at altitudes as high as 1000 feet was measured in theTrinity air survey.

At Bikini aerial redio'logioal surveys at altitudes upto 4000 feet were made with FBM type aircraft after eachtest, Aocuracy of the results of this survey was hamperedby the types of instruments used, by the inability to lo-cate quickly the position at which a reading was made, andby shifting lagoon currents which constantly changed theradiation intensity of specific areas of the contaminatedwater. No surveys of contaminated land areas were made atBikini. Nevertheless, the tests at Bikini proved that itwas possible to obtain reasonably reproducible values forthe decrease in radiation field with altitude (2).

Eirsohfelder, Hull, and Magee have made a number oftheoretical calculations of attenuation of gamma radiationin air above an infinite contaminated land or sea souroeTheir studies involved gamma radiations of a number of dif-ferent energies and took into account multiple scattering.The experimental data from the aerial surveys followingtest Baker at Bikini gave values in agreement with those

Numbers in parentheses indicate references on page40 of this report.

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calculated fo r three million eleotron volts (3 Mav) gammaradiation* A number of uncertainties still exist in theseoaloulations and further experimental confirmation is re-quired.

IXPERIMENTAL

Th e present project was proposed by the U. S. Navy,Bureau of Aeronautios and endorsed by the Arned ForcesSpecial Weapons Project and the U. S. Air Foroe. It wasapproved by the Scientific Director of OPERATION SANDSTONEand assigned to the cognizance of Task Group 7.6.

MATERIALS AND EQUIPMENT

All available types of portable radiao instruments foruse in the serial survey were flight tested to determinetheir adequacy fo r this purpose. Th e following types weregiven particular studys

a. National Technical Laboratories, Geiger CounterModel MX-5.

b. Viotoreen Instrument Company, Ionization ChamberModel 247-A-Sp (high range).

a. National Teohnioal Laboratories, Ionization Cham-ber Model U-6.

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Th e aerial survey of ground oontamuination was made ina C-47 type airplane furnished by Commander, Task Group7.4. Tie C-47 wa s chocked prior to each tests A desk wasinstalled with a sunken oompartoent to hold the radiationdetection instruments. Special lights were available; ared light with the switch in the navigator's eompartentto indicate the exact time over the point zero, and a greenlight operated from the copilot's seat which registered thetime on a particular flight logo Headphone and microphoneleads were available for use by the Radiologioal Safetyofficer.

Film badges were worn by each member of the crew oneach mission and dosimeters were carried on the plane.

CALIBRATION PROCEDURES

All instruments were calibrated on the ground and inthe air with a radium source prior to their use in theaerial radiological survey. Measurements were made ofthe time oonstant of the various instruments*

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DECA.YAll readings were corrected fo r decay as follows The

X-ray orator readings were corrected to X-ray hour plus 1,the Yoke orator readings corrected to Yoke hI6ur plus 6, andthe Zebra orater readings corrected to Zebra hour plus 2.The variance in the corrections was due to different trisein which the test day missions were started, all correctionsbeing made to the approximate hour of starting each mission.Th e decay correction curves were obtained as a part of Proj-*Ot ,1-17/AS-. Residual Contamination of Crater (5), inwhich decay curves were measured fo r actual samples obtainedfrom each orater* These curves were converted into cor-rection factor surves; whereby the decay factor fo r anytime may be obtained and multiplied by the reading to givea figure corrected fo r deoay. Please ase Appendix 1, Figure231 Appendix 2, Figure 191 and Appendix 3, Figure 14. Allgraphs and charts shown use radiation intensities which havebeen corrected fo r decay with th e exception of those for th eOross Section Radiation Field which use actual readings.

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SURFACE MEASUREMENTS

On many of the graphs, ground areas and rates of radi-ation measured on the surface have been inserted, Theseare for direct correlation with the air readings and arealso corrected fo r decay. At various points throughoutthe report, references have been made to the differentcraters and to crater readings. The orator is defined asthe are& around the point of detonation which is directlyoontaminated by the bomb explosion. It does not includethe areas contaminated by material falling from the cloud.This area ma y extend 1000 feet or more from the initialposition of the zero point.

Surface monitors, in measuring the crater areas onsuceeding days, discovered that the intensities increasedrapidly to a certain distance and then leveled off for avarying distance. Within a few inches of the tower stumps,or the ground between them, the radiation rate increasedtremendously. For this reason. an average of the "plateau*of radiation which ranged from 100 to 1000 feet from thetower stumps (depending on the particular crater) wastaken as the crater reading fo r this report. It is quiteapparent that the very high intensities recorded withininches of the stumps, or cement blocks, or the ground

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between them could not be detected in the air in the pros-ence of the radiation frum th e large contaminated area.

OPERATIONS

The survey was to provide rapid information on intensi-ties of nuclear radiations within the blast area and toaccumulate precise scientific data in regard to the attenu-ation of gamma radiation above land and see surfaoes con-taminated by atomic bomb explosions.

these operations the crew consisted of a pilot, oo-pilot, navigator, radiomen, and engineer. In addition totheir regular duties, the following special tasks were as-signed to crew members. The pilot studied end practicedthe rather intricete fl ight pattern necessary fo r such anoperation with the assistance of th e copilot who timed eachle g and croos leg with a stop watch. The copilot also noti-fied th e Radiological S 'ty officer the time each leg wasstarted end completed by means of th e speoially installedgreen l ight, and kept a running log of the times of eachleg, and the time over th e point zero. The navigator com-puted th e headings, true course, a ir speed, ground speed,and time over point zero of th e different legs. He alsocheocked the instant the plane passed over point zero in

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his driftumter, and notified the Radiologioal Safetyofficer of this time by means of the specially installedred light. During the Phase 3 operations, he oharted th ecourse of the airoraft with the times over the strategicareas, using the plot as a fall-out chart. Th e radiomanhandled the radio traffic necessary fo r a special missionand in addition, on the teat days, transcribed the codedmessages given him by the Radiological Safety officer aftereach leg. The engineer assisted the Radiological Safetyofficer in his functions, and copied on prepared forms all.eadings taken by the monitor.

The crew of the 0-47 aircraft were at Eniwetok onPeter (practice), X-ray, Yoke', and Zebra days by it-hour.After H-hour, the crew was prepared to take off immediatelyin case the cloud should drift across the island. Th e sur-vey unit took off on the mission at H-hour plus thirtyminutes and at 5000 feet altitude, orbited at a point fivemiles upwind from point zero until directed by Commander,Air Force, to proceed with the flight plan as outlined inthe following paragraphs.

The survey plan consisted of three phases as follows

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Phase 1Khen directed by Coummander, Air Force, the C-47 commencedhorizontal survey at 5000 feet. First leg was over pointzero on a bearing determined so as to avoid any downwindcontaminated a ir mass. All legs were made at a constantair speed and along a constent bearing fo r three miles oneither side of point zero. The plane then turned and madeanother leg at an angle of 045 from the original leg.This maneuver was continued until a complete asteriskpattern with legs at an angle of 450 had been made. (Inoperations over the Yoke and Zebra craters only three legswere flown at 1200 angle to each other.) After completingthis horizontal flight pattern, the same pattern was flowna t 4000 feet, 3000 feet, 2000 feet, 1000 feet, and lowerif rediological safety conditions permitted.

Phase 2After completion of Phase 3, the survey unit retired fromthe contaminated area and requested permission to surveyabove 5000 feet. When approval was received, the surveyunit flew a six-mile leg at 6000 feet along the same axisas the first le g in Phase 1. The second log was flown at7000 feet on an axis 1800 to the first leg. The unit wasprepared to ascend by 1000-feet intervals on each reversaluntil normal background was reached.

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Phase 3Phase 3 wps inserted primarily for radiological safetypurposes in OPERATION SANDSTONE after the original planshad been submitted. This survey was flown after Phase 1,and is the fall-out survey. (Appendix 1, Figure 31;Appendix 2, Figure 27; Appendix 3, Figure 20.) Here theaircraft flew downwind from the crater for a distance ofeight or ten miles and returned by four-mile cross legsspaced at a distance of two miles. This survey was tocheck areas possibly contaminated by fall-out from thealoud.

Th e survey unit was prepared to repeat the afore-men-tioned flight on succeeding days if deemed necessary. Whenneeded for radiological safety purposes, the air survey ofground contamination was continued in a helicopter, TypeBH3S. The general plan for this survey was vertical flightsover radioactive areas, taking readings of the radiationintensity at various altitudes. These aeriel readingswere to be integrated with surface rerdings made by groundmonitors directly beneath the helicopter unit. Th e hell-copter survey was not conducted until the ground radiationintensity was low enough to permit ground monitoring.

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RESULTS

During the three tests the C-47 Arial RadiologiolReconnaissance Survey was flown on eight different days;three days over Engebi and Akman (X-ray and Yoke Islands);and twice over Runit (Zebra Island)* Th e particular daysflown were X-ray, X-ray plus 6, Yoke, Yoke plus 1, Yokeplus 9, Zebra, and Zebra plus 1. Th e aerial survey wa sflown in a helicopter (Type H03S) on Zebra plus 4.

In completing these surveys, two hundred end eightruns were made over the three craters, end three fall-outsurveys were performed at a low altitude. Th e total timflown in actual radiological reconnaissance for all threetests was twenty-five hours.

Several complicating feators were encountered, es-peoially on the first test. Slight to moderate contami-nation of the airoreft due to unexpected fall-out occurredfollowing Tests X-ray end Yoke. Consequently, for TestZebra, the time of the survey was set back to H plus twohours, instead of H plus one hour. The ion ohambers usedbecame badly saturated over 3000 milliroentgen per houron X-ray day. This was corrected by the Instrument Groupafter experimentation by increasing circuit voltage. Itwas also found on Test X-ray that altitudes under 1000 feet

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should be flown in order to obtain date for an accurateestimate of the crater intensity. Consequently, altitudeswere decreased to th e point where the intensity was th emaximum which could be measured by the available instruments.(The maximum intensity which could be recorded by the in-struments used was 25,000 mr/Ar.)

The results of the missions were most satisfactory.A tremendous amount of data were obtained and en analysis

made fo r this report of as much as time permitted. It isrecommended that further careful study be made of thismaterial. The missions proved useful from the standpointof rediologioal safety in that readings of high intensityareas could be taken, thus advising surface monitors ofsuch areas. The fell-out survey proved practical in givingthe surface monitors informrtion on areas of high contami-nation. Ten types of instruments were tested during thesurveys.

The primary objective of the mission, that of measur-ing the attenuation of gamma radiation in the air above alarge contaminated surface, was aooomplishedj but th eanalysis is not yet completed and it is felt that muchinformation was obtained which will further the study ofthis work. A study by Dr. T. Ni. White on the correlationof ground and air readings is included as Appendix 5.

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There is also a series of graphs made from the results ofeach teat by which a relatively good estimate of groundreadings may be made from aerial surveys. One point ofinterest is that the easm general ourve exists for obtain-ing the correction fector used to determine ground intensi-ties from aerial readings fo r all surveys made over theX-ray and Yoke cretera. See Figure 1, page 34.

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TEST X-RAY

Th e C-47 with crew took off from Eniwetok Island atplus 30 minutes and arrived ten miles upwind of point zeroat plus 50 minutes, where it orbited awaiting further in-structions. At plus 69 minutes, orders were received toproceed on the mission.

In approximately one minute the Radiological Safetymonitor motised an instantaneous reading of 120 mrA/re Heordered the pilot to change course, and the navigator re-ported the plane under the uppermost fringe of the aloud.Although the plane was not in the fall-out area, it wasapparent it had encountered some fell-out from the upperportions of the cloud which had moved in a direction 180cto the surface winds. The plane wa s moderately contami-nated and the background remained at approximately 8 mr/irfo r approximately one hour, decreasing to 1 mr/Ar uponlanding. This background reading was for gamma only, therebeing no beta encountered inside the plane. This back-ground was subtracted from subsequent readings.

Phase 1 was then started at 0738 at an elevation of5000 feet. Readings of 4 .r/hr were encountered at thislevel. The pattern was also flown at elevations of 4000,3000, 2000, and 1000 feet. The highest rate of radiation

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of 3500 mr/ir was enoountered at the 1000-foot elevation.This value when iorrected fo r instrument error would givea reading of 8700 ArAhr. A discussion of this instrumenterror will be found on page 18 of this report.

As stated previously, an additional survey, the fall-out survey, or Phase 3, was added a few days before thefirst test. This mission oonsisted of flying directlydowiwind from the teat island fo r a distanoe of eight milesand returning by cross Legs of four-mile lengths with two-mile intervals between. Th e flight was made at an altitudeof 200 feet with a constant air speed of 140 knots. Read-ings of 500 mrAr were detected over the islands of Bogon,Bogairikk, and Teiteiripuoohi which were directly west ofEngebi (Zero Island) and were in the expected fall-out area.Lower readings were detected throughout the area, partiou-larly over reefs and smaller islands.

Phase 2 was then started the first leg being at 5000feet and other legs at 6000 feet, 7000 feet, and B000 feet.The highest altitude flown where radiation was encounteredwas 8000 feet at plus four and one-half hours. This read-ing (0.1 ar/hr) is somewhat doubtful due to the high back-ground in the aircraft. However, a definite rise abovebackground was encountered at 7000 feete

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It had been anticipated that following Test X-raysome changes in the operation plan would have to be made.Such changes were found necessary and were instituted assoon as prectioable.

Three complicating factors presented themselves onX-ray day. These were all corrected prior to the lastmission. Before the actual survey was started, the air-plane had been contaminated by fall-out, although therewas none anticipated from the cloud at the height it wasencountered. Consequently it was decided to stay out fromunder the cloud, no matter what it s altitude, and if neoes-sary to delay the beginning of the mission one hour. Thelatter was actually done for the Test Zebra day flight.

At the 1000-foot level on X-ray day, and the lowerlevels on X-ray plus one, the instruments appeared sluggishin high intensity flights. Following the X-ray plus oneflight, the ion chambers were returned to the ship andrecalibrated. It was found that the MX-6 type instrumentwas saturating on the 500 and 5000 mr/hr scales. Thiswas especially true of reading. over 3000 mr/hr. The in-strument was found to read only 500u mr/hr in a radiationfield of 21,000 mr/hr. The instruments were calibratedusing a large radium source, and all readings taken on thefirst two days were corrected for calibretion.

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Other instruments were obtsined which had a higher voltagesupply and were direct reeding. These instruments wereused fo r the remainder of the operation and werm chockedafter each mission fo r calibration and funotioLing.

It was determined after the X-rsj day flight that itwould be necessary to fly at a lower level to obtain theproper curves and to extrapolate with sufficient accuracy

the maximum reading versus altitude curve to ground level*On X-ray plus one, altitudes of 750 bnd 500 feet were flownand, while the resultant cu.ves mere better, it was decidedthat even lower levels should be tried. The intensity ofthe crater had decreased enough by X-ray plus six thatflights at 250 and 100 feet were added to the Phase 1 plansReadings of 80 0 mrAr were recorded at the lower level.

Ground monitors were in the crater at this time, andtheir average reading was found to be 1800 mr/hr which read-ing was also determined approximately by extrapolation ofthe curve of maximum readings as a function of the altitude.On later missions, the altitude was decreased until th emneximum limit of th e instruments used was reached.

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TEST YOKE

The 0-47 with crew took off from Eniwetok Island atplus 31 minutes, and at plus 64 minutes was ordered tostart on its survey. It hod been orbiting ten miles up-wind from Zero Island (Aoman) end the cloud wps pleinlyvisible and easily observed. This cloud, unlike the oneover Engebi which conformed to the expected pattern, wasspread ou t over a tremendous area at a much lower level.It was anticipated that certain iegs of the survey couldnot be completed because of the close proximity of a por-tion of the cloud. At th e turn between legs one and two,at the 5000-foot level, the cloud appeared very near;and although the course was changed, fal l -out was contacted.The reading inside the aircraft rose to 150 mr/hr, bu t un-like the Test X-ray contamination, did not drop as rapidlyand persisted at a relatively high level fo r some time*Several rein clouds were flown through; but when it be-came apparent that the background inside the plane was to ohigh to make accurate measureiaents, th e airplane was or-dered to return to Eniwetok. Here the plane was monitoredand allowed to sit and "cool off". Readings taken insideth e plane were as follows:

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Time Readingmr~hr0725 Fall-out eanoountered 150

0728 Aborting flission 480730 440731 Flying through rain clouds 440740 Flying through rain clouds 350756 Over base 300756 Over base 280805 Landed 250820 On Eniwetok 200857 On Eniwetok 181015 On Eniwetok 111232 On Eniwetok 61310 Take-off for resumption of 4

missionAs indicated, the decay rate was rapid, and the plane

took off under instructions at 1310 the same day. After ashort time the background in the plane had dropped to 3 mr/hr , and it gradually dropped during the remainder of themission.

In certain respects the mission was flown the afternoonof Yoke day more successfully than it could have been flownat plus one hour* For one thing, no cloud was present todisrupt the mission and there were no other airplanes In

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the vicinity, except two helicopters at very low altitude.The crater had decayed enough that it was possible to de-soend to 600 feet to make a survey and stay within themaximum limits of the instruments. On this occasion it waspointed ou t again how valuable it would have been to havean instrument that would measure higher intensities than26,000 mr/hr. At 600 feet the highest intensity recorded

was 21,000 mr/hr. On e pass had been made at 500 feet, andthe 247-A-Sp went off scale.

Following Phase 1, Phase 3 was carried out as planned.This survey was a t 200 feet altitude and 140 knots constantair speed, it wvas found that fall-out had occurred on allislands north and west of Aoman, to and including Engebi(X-ray Island)e Intensities as high as 6000 mr/hr weremeasured over the island adjacent to Aoman (northwest),Eberiru, and levels of 100 mr/hr or more were recorded overthe other islands, including Engebi.

Because of the delayed mission on Yoke day, the readingat the 5000-foot level was negligible, and Phase 2 was notnecessary,

An will be noted in the graphs and charts, only threelegs were flown on Yoke day and on succeeding days. It hadbeen decided following X-ray day that lower altitude f l ightswere needed; so in order to compensate to some extent for

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the added dosage of radiation this would necessitate, threelegs at each altitude were used instead of the originalplan of four. These legs were to be 1200 apart with thefirst leg always along the long axis of the island, unlessfall-out or some other factor necessitated a change. Thealtitudes planned were as previously described, but alsoincluded flights at 1600, 750, and 500 feet. On later daysit was possible to go even lower.

On Yoke plus I day the mission was repeated. Th ehighest altitude where appreciable radiation was detectedwas at 3000 feet. The reading here averaged 31.3 mr/hr.The lowest level flown was 250 feet where an intensity of25,000 mr/hr was recorded.

On Yoke plus 9 day the mission was repeated, and at thesame time a survey party measured intensities in the oratoritself. Thus it was again possible to correlate directlyground readings with air readings. The lowest intensityrecorded on this day was at 50 feet where the reading was60 0 mr/hr. This corrected fo r decay gave 120,000 mrlhr,and the curve of maxim= readings as a function of altitudewhen extrapolated out came to approximately 260,000 mr/hrwhich was very near the average corrected ground readingfor the crater outside the tower etumps.

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Despite the oontamination of the 0-47 on Yoke day, itis felt that the reeults of th e Yoke orater readings weresatisfaotory, more so than th e X-ray orator readings. Thiswill be disoussed more in the next section of th e report.

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TEST ZEBRA

Prior to Test Zebra it had been deoided that if theoloud appeared to be lingering in the area, the surveywould be postponed until H plus 2 houirs. It was alsoplanned to do Phase 2 first, starting at 10,000 feet andworking down, in order to determine accurately just howhigh the gamma rays oould be deteoted.

The C-47 and crew took off from Eniwetok at plus 30minutes, as on the previous tests, and resahed its orbit-ing point ten miles upwind of Zero Island (Runit) in tenminutes. It orbited here until plus 118 minutes at 10,000feet when it was ordered to start it s mission. Th e aloudwas not enoountered.

No radiation was deteoted at altitudes above 7000feet, at whioh altitude the instrument showed about twioebaokground fo r the entire length of the leg. At 6000 feeta reading of I mrl/hr was obtained. Th e survey was con-tinued until a level of 400 feet was renohed where therate reoorded was 21,000 mr/hr. It was not deemed neces-sary to go lower than this altitude as there were no in-struments available that would measure that high rate.

Following Phase 2 and Phase 1, the fall-out surveywas started. As on the previous teats, the islands upwind

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of the Zero Island were contaminated by fall-out, withPiiraai showing an intensity of 400 mr/hr, Biijiri andRojoa 800 mr/hr, and islands north of Aoman having higherreadings than they had just before Zebra day. The missionon Zebra day was carried out uneventfully, and it was feltthe results here should be better than those obtained fromany previous mission. However, the rapidity with which theoperation was being terminated preoluded the possibilityof additional flights at a later date during which intensitymeasurements were made of the orater at point zero byground monitors. In general, this detracted from the valueof the survey as it is necessary to have a ground readingof the orater taken at the same time for checking with theextrapolated readings from the aerial survey.

On Zero plus one day the mission was repeated, and areading of 0.5 mr/hr was recorded at 5000 feet. Th eflights were continued at altitudes down to and including150 feet where the reading was 20,700 mr/hr. One leg wasattempted at 100 feet, bu t the 247-A-Sp went off scale at25,000 mr/hr.

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INSTRUMENT TESTS

After oheoking several types of instruments as torange, sensitivity, needle fluctuation, time oonstant, andaltitude effects, certain ones were ohosen fo r the firsttest with the understanding that they might be exohangedlater if deemed neoessary. Those ohosen for the routinesurveys were the XX-5 and NX-6 of the National TechnicalLaboratories and the 247-A-Sp produoed by the ViotoreenCompany. The MX-5 employed a Geiger-Mueller tube in de-teotion of radiation, while the NX-6 and 247-A-Sp used ionchambers. The NX-5 was se t on the 20 soale (range up to20 mr/hr) and the MX-6's were se t on 50 , 500, and 600scales (ranges up to 50 mr/hr. 500 m-/hr, and W00 mr/hrrespeotively)* Th e 24 7-A-Sp was set on the 1000 1 scale(range up to 25,000 mr/hr). It later was neoessary to usean aX-6 on the 5 soale (range up to 5 mr/hr) when the MX-5started saturating. These instruments were fitted intothe spaoe in the deok espeoially designed to hold them.During the mission all instruments, exoept the MX-5, wereleft on during the entire flight. Th e MI-5 was turned offwhen its upper limit was reaohed, then turned on after pointzero had been passed and intensities within the range of theinstrument were again enoountered. This was neocessary asthe Geiger oounters were known to saturate when exposed

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to high intensities, while it was not believed the ion

chambers would*Ans to the performance of these particular instruments,

it can be said that as a whole they were satisfactory.However, the MX-5 saturated badly on X-ray plus six, Yoke,and Yoke plus one, but after a new tube was installed itperformed much better. The NX-6 saturated in high intensi-ties and it was necessary to install more batteries. Th e247-AP-Sp appeared to be quite adequate. It had been cali-brated several times with a large source and needed no re -setting or calibration curve. As stated previously, afterX-ray plus one, no curves were necessary fo r the 11X-6's asthey were direct reading.

The mechanical time constant was cheocked fo r all pre-viously mentioned instruments, plus the 247-A and the 263-AGeiger counter. These values were determined by exposingthe instruments to an X-ray machine which was switched onand off fo r an instant. Adequate radiation intensities wereproduced by regulating the amperage of the machine so allthe instruments oould be tested.Results are as follows:

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11X-6 0 secondsNX-5 0.2 seconds247-A-Sp 0.2 seconds247-A 0.2 seconds263 0.2 seconds

In addition to saturating with their standard powersupply, the MX-6 was also affected by humidity toward thelatter part of the operation. It was necessary to removethe instrument from the case several times during the lastfew weeks. During Zebra day and Zebra plus one, two of theIM-6 instruments used were rendered useless by moistureoollecting in them.

As will be pointed out, extremely high intensities,higher than the range of instruments available fo r thisoperation, can be measured in a rapidly moving airplane.Consequently, if instruments with higher ranges were avail-able, lower altitudes could be flowvn and test results wouldbe more significant% In tests these surveys could be madeby teams with no one group exceeding a toleranoe dose.

On Yoke day plus nine, an additional monitor was carriedwh o cheocked four instruments in addition to those used by theregular Radiological Safety officer. These instruments were:Viatoreen 263-A Geiger counter, Viotoreen 247-A ion ohamber,Viotoreen 247-A-Sp ion chamber, and the Instrument

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Developing Laboratories 2610 Geiger oounter. As a wholethe instruments were satisfactory, although they all dis-played more of a mechanical time constant than the MX-6.In higher intensities, all of the Geiger counters had atendency to saturate. Of the instruments tested, th eViotoreen 247-A appeared much more stable and performedbest, although readings on this instrument were not as highas those recorded by th e regular monitor. The instrumentsregularly used on the mission were tested on all scales andgave readings within expectancy.

It should be stated that for the most part instrumentsused in this survey were fo r low altitude flights, usuallyunder 5000 feet. On two occasions flights were made at analtitude of 10,000 feet. The air monitoring section, TaskUnit 7.6.1, altitude tested all their instruments, and th eoffeot of altitude upon these instruments is discussed inthe report of Task Unit 7.6.1. Prior to X-ray day, anMX-5, three MX-6, and one 247-h-Sp were calibrated at 1000feet intervals from 1000 to 7000 feet. The instruments werealso calibrated at ground level and curves fo r both alti-tude and ground readings were drawn. The varianoe betweenreadings at 7000 feet and ground level were negligible.

Consequently, readings taken were not corrected for alti-tude calibration.

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I. - -~ --- ----- - .3 - - .

DISCUSSION

As a result of this project a vast amount of data hasbeen accumulated on the radiation field above the oraterfrom an atomic bomb detonation. At this time it is onlypossible to make a very general analysis of these results,but it is planned to initiate continuing studies with aview to obtaining a better understanding of the phenomenainvolved. The detailed data obtained fo r X-ray, Yoke, andZebra are included as Appendices 1, 2, and 3 respeotively.For the purposes of this discussion the analysis has beenbroken down into the following categories:

Maximum Intensity At Bach Altitude

The maximum intensity was measured fo r each traverse ofthe crater, and the average of these fo r all legs a t a givenaltitude was taken to be the maximum intensity at that alti-tude. The detailed data for the various tests are presentedin Figures 1 through 3 of Appendices 1 and 2 and Figures 1and 2 of Appendix 3. The maximum intensity at each altitudehas been plotted as a function of altitude in Figures 8through 10 of Appendix 1, 7 through 9 of Appendix 2, and 6and 7 of Appendix 3. The data were exceedingly reproduciblefo r the maximum for the several legs at a given altitude

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.nd he variation with altitude followed a relativelysmooth curve. The one possible exception is the X-rayplus six day survey on which the lower intensity readingswere measured with an VX-5 type instrument which wa ssaturating badly. Extrapolation to the ground level wasattempted, and on two occasions ground measurements wereactually made on the same day as the survey was flown.The extrapolated value obtained from the aerial surveyagreed very closely with the values obtained by the groundmonitors.

In order to apply these results obtained by means ofthe aerial survey to operational conditions, it is necessaryto have a se t of factors Ly which the air readings can beconverted to the reasing fo r the intensity on the ground.Such correction factors '.ave been computed for all surveysmade and the cmposite data Flotted as a function of alti-tude in Figure 1 to this repot. The curves for all sur-veys fall more or less along the same general line andtherefore a final curve can be drawn which will be usefulfo r all occasions. The factors obtained from such acurve should prove of considerable value in the event thatprompt aerial survey would be required of a bombed area.

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Boundaries Of The Radiation Field Above Th . CraterThe outer limits of the radiation field (this was

selected as the 4 m/hr line) have been plotted fo r eachsuccessive survey in Figures 4 through 7 of Appendix 1,4 through 6 of Appendix 2, and 3 through 5 of Appendix 3.The boundaries for the separate legs provide a three dinm-uional picture of the volume within which the intensitywas greater than 4 mr/hr. Th e pattern conforms in generalto a large dome, and there wa s not much evidence of a de-crease in the diameter at low altitudes. However, thesurveys in general were carried out at relatively highaltitudes, and it is quite understandable that this effectwas not observed.

Following Test Zebra a very low altitude survey wasmade by means of a helicopter. This survey indicated thatbeyond 350 yards from the center of the orater the intensityincreased with altitude up to 200 feet, while at 200 yardsand closer the intensity Increased as the ground was ap-proached. Details of the survey are given in Appendix 4.

The presence of scattered areas of high activity inthe periphery of the orator and on adjacent islands ao -counted to some extent for the irregularities in soms ofthe boundaries of the radiation field. These highly activeareas on the ground were also detected and measured by

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06

JF -

7--

nowc- YK- -IL . .. . .-

9

oJ 3- - - -4 ___.

. . .... . . . . ...

o .- -OKE + 9Al

ALTITUDE (ft.)


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ground monitors.Th e highest altitude to which any radiation was do-

tooted was 8000 feet over Engebi at approximately H plus4 hours and at 7000 feet over Runit at H plus 2 hours.

Intensity Of R~adiation Field Above Crater

In Figures 11 through 22 of Appendix 1, 10 through 18of Appendix 2, and 8 through 13 of Appendix 3, the intensi-ty as measured on each leg has been plotted as a funotionof the distance from point zero. These figures demonstratethe extremely rapid rise and fall of the intensities en-countered in flying over the crater. In general the fallis roughly sym-netrioal -about the center, but on occasioncontaminated downwind areas oaused irregularities in theradiation field. The land mass areas have been insertedalong the base line of the curves in order to explain someof these irregularities. However, it is to be noted thatunder most conditions this did not appreciably affect thedistribution of the field, indicating that at least at thehigher altitudes the orator mats as an approximate pointsource. It is to be noted that in the three test daysurveys the base of the curves wa s considerably broaderdue to the higher intensities of radiation encountered*

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AttenuationIn order to make a preliminary analysis of the factors

involved in th e attenuation of the gamea radiation as afunction of altitude th e intensity times the altitudesquared was plotted as a function of altitude on semi-logpaper. These plots and the basio data are included asFigures 24 through 27 of Appendix 1, 20 through 23 ofAppendix 2, and 15 through 17 of Appendix 3. From these itwill be seen that above an altitude of 1000 to 2000 feet th einverse square law is playing an important part in the de-crease in intensity and that, therefore, at these altitudesthe crater nan be approximately treated as a point souroe*No attempt has yet been made to calculate th e mean freepath from the slope of these curves and to interpret th eresults. However, preliminary investigation reveals thatthese slopes are not too different fo r the various surveys.Below 1000 feet air absorption is playing th e largest partin reducing the gamna radiation. Dr. White has attempted tocorrelate these results obtained by means of the aerial sur-vey with those obtained from the ground survey, assumingthat in both oases the crater could be considered as aradioactive souroce onoentrated a t some point. This analy-sis is presented in detail in Appendix 5b

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Aerial Survey Of Fall-Out Areas

A. Phase 3 of the aerial survey operations, passeswere made at low altitudes over ereas downwind of th ecrater. The results of these flights are shown in Figure31 of Appendix 1, Figure 27 of Appendix 2, and Figure 20of Appendix 3. These surveys indicated clesrly whichislands were contaminated and approximately to what extent.The results were oonfirmed when land parties went ashoreand monitored the dow'ind islands.

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CONCLUSIONS AND RECOMMSUATIONS

Th e results of the C-47 survey show that it is feas-ible to conduct an aerial reconnaissance of a bombed orcontaminated area in order to determine the extent of th econtaminated area and obtain a reasonably accurate esti-mate of the intensities involved. This type of surveywould be invaluable in th e event of atomic warfare sinceonly by this method will it be possible to obtain a quickestimate of the radiological defense problems involved sothat adequate planning can be undertaken without the delayrequired if ground monitors have to survey the area. Withthe present equipment it does not appear possible to detectby aerial methods the local 'hot spots* within a contaminatedareGA

Arial survey of a contaminated area appears sufficient-ly accurate to obtain data which can be used for detailedanalysis of the radiation field produced. It in recom-mended that such analysis be undertaken with th e presentdata and that similar operations be conducted in futuretests.

Although the instruments used during the operationproved satisfactory, a number of improvements should bemade in order that this type of survey can be adopted for

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operational use. They should be more adequately sealed inorder to prevent damage by moisture and to protect againstpressure changes, The time oonstant should be essentiallyzero and th e instrument direct reading with a reoordingmechanism which would eliminate the errors due to the nooes-sity of making rapid readings as the plane traverses th earea. Sinoe the plane itself may provide some shieldingfo r the instrwuents, it is reeommended that the countingtube or ion chamber be placed in a window in th e deck ofthe plane. Instruments with a range of at least 100,000mrAhr should be available for this work.

It is reoonmended that th e development of this typeof survey be given high priority so that it can be adoptedas a standard operation in the event of atomic warfare.

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REFERENCES

(1) "Trinity Air Survey" by Howard L. Walton, 17April 1946, (Copy in Armed Forces Special Weapons Projectfiles)*

(2) 'Nuolear Radiation Effects in Tests Able an dBaker," Preliminary Report of, Seris SLW/RS/-2 of 25September 1946, Appendix III.

(3) "Residual Contamination of Crater,* Project 7.1-17/R

operation sandstone. nuclear explosions 1948, scientific director's report of atomic weapon tests

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