External Radiation Survey and Dose Predictions for Rongelap, Utirik, Rongerik, Ailik, and Wotje Atolls

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External radiation measurements were made at several atolls i.nthe rtorchern.?farshrnllIslands, which are known ar suspecced to have been che recipience of tropospheric failouc during che ?acific Testing Programs. Sufficiencydata were available to ascertai:.realistic dose predictions for the inhabitants of RongelaD and Ut:rik Aco:ls where che 30 year integral doses from external sources excluslve 2f $ackgrc)uncradiation were 0.65 and 0.06 rem respectilvelv These estimates are baged on realisc:iclifestyle models based cn observations of each ato 1 :mmlunity. Ailuk and

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In 1976, 3rookhaven Xational Laboratory initiated a program of external radiation 9ur~ey for the Rongelap, Rongeri&,,Ai.luk,Uocje and Utirik Atolls. The purpose of these surveys was co provide sufficient information concerning the ambient radiation levels resulting from the)mid 1950’s weapons testing program to make external dose calculations for the individuals living in the sumeyed areas, During the last two years, sufficient measurements were made to provide external dose information for most of the populations in the region. The data from Rongerik, AiLuk, Wotje, Rongelap and Utirik Atolls were acquired during trips in September 1976, MaY 1977 and October 1977. All the exposure rate information gathered from these i~tollg was obtained with a pressurized ion chamber. ‘Theequipment used in these studies consisted of a Reuter Stokes Environmental Radiation Honitor, Model RSS-:11 and a gexmnaspectroscopy system consisting of a sodium iodide detector mental exposure levels were meter was ‘usedco determine coupled to a portable multichannel analyzer. ZnvironThe field trips were staffed by 8NL personnel and guest scientists from ocher institutions. Participants are listed later in the report. Th$a report represents all of iar the people livlng on Rongelap,

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Instrumentation and Methods .U1 environmental exposure rate measurements were abtalned ‘usinga Reuter Stokes environmental radiation monicar modeL RSS-111. The instmment is designed to neasure environmental radiation as Low as 100 JIadlyear. The RSS-111 consists of a spherical high pressure ion chamber filled to 25 atmospheres of Izgon. Incident radiation produces LOn pairs within the active volume of the chamber which result in a current flow. The current flow is measured by an electrometer and is directLy related to the free air exposure The active voLume of the stainless steel ionization chamber is known to ~lz. The current produced Lnthe chamber is a function of incident radiation from an external field,cosmic ray-response and contamination found in the stainless steel. The equation relating instrument incident radiation is: response to energy of the current produced in tha chamber by che incident proportionality ccnstant stating che variability instrument respcn~ to the energy of the incident intensity of the gamma field in -R/hr current produced 5y activity in the staialess steel proportionality constant for cosmic rays intensity of cosmic rays

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For a given area, the values of Kc and XC ‘tillbe constant Since we measure RT, the only unknti are Kj and Ij. The value detemained o’ncethe ambient samma spectrum is knon. Data from of <j can be indicates an error of as much as 6 to 10% could result if energy corrections are not nude to the gross readings. The RSS-lllS used in ehis study were calibrated at the factory using radium sources whose calibration is traceable co the Xational Bureau of Standards. Calibration of che instruments were also checked by M (formerly HASL) prior to field Energy Dependence Corrections In the 1977 surveys, BNL used a sodium iodide detector, whose output was coupled to a multichannel analyzer, The purpose was to enable the BNL team to acquire ~pectra of the terrestrial background radiation at one meter above the surface. This was done at the same height and in the same areas where the RSS-Ul measurements were taken. Consequently, energy dependence factors could be calculated by examining the lnvironmental gananascan for the lnergies of those nuclides most predominant in the terrestrial environment. The equipment used to accomplish this part of the work was a computing Gamma Spectrometer, Yodel ‘~ 74-008 Jillbuilt bv Lamence Livemore Laboratory (2). The system uses a Harshaw 5.08 cm diameter x 5.08 cm thick NaI(Tl) scintillation detector. The spectrometer can be operated from AC power or on internal batteries. Spectra are visually displayed on a CRT, and transferred to magnetic tape for storage..- Using the math package with zhe system, each spectr’~mwas examined L3 the energy dependence factors. The range of factors needed to compensate the RSS-’LL1respor.sed’-!eco e~ergy

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dependence was 1.OL to 1.05. The mean correction was approximately 1.02. Consequently, ve felt no need to correct the remaining :976 or 1977 data for the minor energv dependence encountered. A total of 112 RSS-L1l measurements vere taken on five atolls. Each data paint is the average of at Least 20 individual readings. This assures the precision of the value while the LnitiaL calibration guarantees accuracy. The one sigma error is on the mean exposure rate. All exposure race values include natural background except where otherwise noted. Figure 1 graphically presents the data obtained at Eaivetak IsLand, Rongerik Atoll. Oa this island, random measurements were taken along a central northsouth transect. Table 1 presents the raw data collected with one sigma error. The average exposure rate for this island 1s 6.3 dR/hr. This is about 1.5 times higher than the cosmiciterrestrial date rate found on uncontaminated coral islands. Eniwetak was the island surveyed in the Rxmgerlk Atoll due to preeence of U. S. servicemen at the weather gtation there at the time of the BRAVO falLout incident. Tables 2, 3, 4, 5 and 6 present the raw data from Rongelap Atoll. The islands surveyed were Kabel.le,Yaen, Eniaetok and Rongelap. yaen is located at the aorthwest corner of the atoll, and Kabelle at che northeast corner. KabelLe is a significant copra resource; and both of these islands may be used for 5rief visits, but neither of them is permanently inhabited. These islands received a significant amount of fallout debris and consequently, are still gubstantiaLL~ east and eastern parts of the atoLL. Tbe current ‘~aiues for external exposure razes on these islands are Listed below and in Table 14. The entire population present!.:{ Island Average Zxacsure lace in -R’hr

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lives on Rongelap Island. The people obtain most of :heir food from ?.ongelap with occasional supplemental trips to Eniaetok and to other southern islands in the atoll. Little or no activities currently takes place on ?Jaenor Kabelle, or ocher islands in the north. Figure 2 is a graphic presentation of the ~asurernent points and exposure rates along the main road of Xongelap Island. The eqosure rate is fairLy unifo~ averaging 7.3 &Rlhr over the island. This is about twice the background radiation level of uncontaminated atolLs in the Marshall Islands. TabLes 7, 8 and 9 present the data for the islands surveyed in the L!tirik Atoll. These islands, Aon, Eorukku and !Jtlrik,represent the major isLands within the atoll. Aon, located in the southwest corner and Utirik located in the southeast corner of the atoLl, are the major areas for Living and food production. The externzl exposure rate for all these the regionaL background level. Tables LO, LL, 12 and 13 present islands is about 4 -Rlhr, i.e., very near ‘JotjeIslands of Wotje Atoll and for Bigen and Ailuk Islands of AiLuk Atoll. These islands were surveyed to determine whether they were representative of baseline external exposure rates for the >farshall Islands. The individual island averages are found in Table 14, but range from 2.7 -R)hr to 3.9 -Rfhr. These exposure races are about the same as f5.ac for Kwajalein and other areas noc exposed to gross contamination from fallout; radiation Levels for the we assumed them to be representative of amblenc background The average exposure rate as measured ior each island is listed in Table 14.

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results are presented in Table 15. Tkese dose estimates were aade based Jpon 2) The averag,eexposure race represents the average for alL islands witiin 3) Wotje and AiLuK Atolls are representative ofk natural background in che Northern Marshall Islands. It is difficult to estimate an external dose for the inhabitants of Rongelap Atoll apart from typical residents who spend most of their time on Rmgelap Island. The reason Lies in the ?onunifonn distribution of radioactive material from island to island within the atoll.. ‘fiilethe southern islands of Rongeiap were determined to have uniform exposure rates on a per isl+nd basis, there were significant differences in the exposure rates between islands and substantial heterogeneity in exposure rates on any given island in the northern sector. In LJCRL 51879 Rev. L (3,4), this problem was approached by estimating che frac:ion of the time that an individual spends on ‘/ariousactivities. This estimate is reprinted here as Table 16, Wing :nis as a basic assumption, we have based ~pon our measurements reported in Tables .-L3. The value for :he lagcon exposure rate was assumed to be the game as ~~,acfor uncontaminated atolls in che which we surveyed. All other estimates are made 3V caking :he average of ail measurements made within che area of i?.ceres:

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Table 1; represents the exposure rate at each pattern of activity as listed in Table 16 calculated assuming 1007.occuparcy for Rongelap Atoll. Tab!e :3 ?ercent of time spent in each area for the Lawrence Livennore lifestyle ?fodel each area provides the average exposure nhabitants of Rongelap Atoll based on Using the averaga hourly exposure rates, the long temn external dose was calculated. Mese iata, presented in Table 9 for Rongelap Atoll, have been corrected for background (terrestrial and cosmic) radiation by using the average exposure rate of Wotje and Afluk Atolls as a representative sample of :he normal (unexpo?ed) Marshall Island environment. We feel that this is a very consemative estimate for RongeLap Atoll since the people ratel.yvisit the mre heavily contaminated islands in the north, and tend to restrict their “other islands” visits to the southern sector where exposure rates are similar co that on Rongelap Island itself. This observation was supported by an independent living pattern assessment from which data became available in the fall of 1977 (5’. iz (October?.977(5) This fnfomation is presented in Table 20. It shou;i te time away from Rongelap Island where a constant exposure rate of 7.3 -R~hr is assumed. Revised extarnal dose predictions balsedon the obser~ed Rongelap ~~’~~~,!?

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I(W 7)9 suggests :hat in 30 years, the general public shouid recei’:e a dcse of Less than S.0 rem fmn total body sources ocher than medical or naeural background (8). In all cases examined here, :his requirement is met. The problem arises that the external g~ radiation is only one source of exposure to the !farshallese. The dieca~ pathway could contribute a substantial increment as an internal dose commitment. Reviewing all atoll doss cousnitmentsin this light, we feel that inhabitants of Rongelap Atoll may have difficulty meeting the ICW {)9criterion of 5 rem in 30 years, but should be within the 0.5 redyear standard for individuals. The interal dose assessment for the people of Rongelap wilL be the subject of a separate report. At this time, we do not recouamendany remedlaL action until a complete dose commitment can be determined by means of examining the external, dietaq and whole body counting data available to date. ‘ The other islands and atolls surveyed are well within the ICRP recommended levels. As SUCh, little more than minimal followup should ba done on these atolls. The main task of the environmental programs should be one of detecting significant changes in the enviroomeat or lifestyle which =Ight warrant a reassessment of these

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The field portion of the radiological survey of the Marshall Islands was accomplished by a very intense and thorough effort by people representing di5ferent organizations. The number of samples coLlected and the amount of information obtained durin8 the survev was a direct result of the cooperation and diligent effort of the following individuals: We are also deeply indebted to the following BNL the field work by performing radionuclide analyses on personnel who complemented numerous samples that were collected and by pretesting all equipment prior to use in the field: The survey crew extends its thanks for the Nevada Operations Office and ?aciflc Area Support Office for support services which resulted in a smooth and efficient survey. Support from the Kwajalei.nMissile Range and the site contractor, Global Associates, ~ weLl as from the crew of the R. V. Liktanur is The outstanding cooperation of personneL from the Trust Territov of the Pacific Islands and from the Office of the District Administrator of the Marshall IsLands, as well as that of the Bikini people, played on important part in the successful completion of the survevt

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L. NO Author Cited, Environmental Radiation Yonitor Model FL5S-LllCoeraticnal (Lawrence Livermore Laboratory, Livemnore, California). ‘Future3ikini Atoll Inhabitants, Lawrence Livennore Laboratory, Rept. UCRLAtoll, Lawrence Livermre Laboratory, Rept. UCRL-5L879 Part 5, (June L977). 5. G. Knight, unpublished data. 6. N. A. Greenhouse, et al, Radiological Analyses of Marshall Islands Environmental Samples from 1974 through 1976. Brookhavet’tNationaL Laboratory Report 7. V. A. Nelson, Radiological Survey of Plants, Animals and Soil at Christmas Island and Seven ACOLLS in the !4arshaLLIslands, University of Washington, 8. Recommendations of the International Couanissionon Radiological Protection, ICRP Publication 9 (Pergamon Press, New York L964).

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transect, 120 m from the ocean in a wooded transect, 170 m from the ocean in a sandy Cross Island transect, 100 m from the ocean in a sandy 5.265.28 Lone standing pole Cross Jsland transect, 50 M from lagoon Cross Island transect, 20 m trom Lagoon Cross Island transect, 20 m from Lagoon cransecc, near cencer of the island near the on top of organ;c Cross Island transect beginning at the vater catchment Innemnosc oenecration along this cransecc 220 m from !agoon 13.~.3 30 n vest of innennost penecracion :5.35,3 55 m west of innemnosc penetration :3.1~0.3 1!5 m west of irmemost penetration by vater cacchmenc 22.15.3 L25 n vest of innermost penetration :n areaof sand and 3U.35.3 20 m south of vacer catchmenc ~o.-+0.4 170 m west of innemost penetration 31.3;0.3 Second transect 275 m south of Cross :s~and :ransect

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Eascvesc cross island transact - Wddla Island 50 m due vest of Ocean Beach 85 m due west of Ocesrl Baach - clearing south of path 85 D due west of Ocean 9each - clearing north of path L35 m dua west of Ocean Beach L75 m ~Ue west of Ocean Beach 215 m due west of Ocaan Be8ch near cLuster of three houses. Area has patchy corsl gravel. 265 m vest of Ocean Beach: kO m from Lagoon Beach Second transect: 250 m due north of )Uddle Island trapsecc 70 m due east of lagoon Adjaceat clearing returning cavard Lagoon Beach Third transect near south end of tha isLand 80 m due east of che lagoon 30 m from &goon Beach near a house: some gravel present ?irsc transect due west to northwest from near southeast corner 22.5$.Aciearing 40 m in from the beach L50 m inland due wast to northwest 55.35.4 returning co beach due southeaet, 25 m to next clearing L2.lfl.5 southeast -40 m to next clearing 40.69.5 Yfdisland second transect due north from the Lagoon center of 62.25.7 25 n south of center isLand cowards che Lagoon …