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May 26, 1967

the water was too rough to land the equipment. Some low-level measurements were made with the HASL larze volume ion-chamber and also the
handheld Wa-I crystal scintillation-type detector. Thermo-luminescentdetectors (TLD), a new type of radiation dose device, were placed at
likely habitation areas on Bikini and Enyu Islands for approximately two
weeks. Film badges were worn by all survey party members during the
Bikini Atoll surveys, The TLD's and film badges were flown back to the
U.S. for readouts. The only radiation values which are available at
present are those made with the handheld survey instruments and these
should be considered only tentative in that the instruments have not been,
as yet, calibrated for the spectrum of isotopes present or their dose
rates. Hany of the measurements were at the lower limit of sensitivity
of the instruments where some uncertainty exists.
The three largest islands, where most of the natives formerly resided, are
Bikini, Enyu and Namu. Bikini is the largest by a factor of 2 to 3
area-wise. Some families also resided on two wr three of the smaller
islands on both the northern and southern rims (accordins to Jendrik L.).

The lowest radiation levels were detected on Enyu, the second largest
island. Values everywhere in the Island were in the range of 0.01 to 0.02
mr/hr, or less, both gamma and beta-gamma at the surface and at 3 feet.
Gn Bikini there appeared a radiation gradieat ranging from approximately
0.04 mr/hr gamma and beta-gamma near the lagoon side beach to a level of
approximately 0.25 mr/hr near the center of the island and to 0.02 mr/hr
at the ocean beach side. On Namu there wes also a radiation gradient
ranging from 0.02 mr/hr at the lagoon beach to 0.35 mr/hr at an interior

location to 0.06 mr/hr on the ocean beach side. Other islands on the
southern edee of the Atoll - Eniirikku and Rukoji - which were downwind of
nuclear tests, had levels of about 0.3 mr/hr. The Aomoen-Yurochi chain of
Islands on the north side had one area where the radiation level was
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0.5 mr/hr. On islands further away from shot sites and not directly
downvind levels were more in the range of 0.02 to 0.06 mr/hr.
,
Cn most of the smaller islands, within five miles of test points, fragments
of metal--ferrous and aluminum alloys--had readings up to 5 mr/hr. Steel
reinforcing rods still imbedded in concrete structures facing test points

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likewise indicated some activity--up to 0.5 mr/hr.

The gamma spectrometer readings on Bikini and Namu indicated that the
gamma activity was largely from isotopes of cobalt and cesium; cesium-137
being the major contributor to the total counts. The low activity level
on Enyu gave no clear picture of contributing isotopes.

Gamma spectrometer

readings on soil samples from the smaller southern islands indicate a

complex mixture of activation and fission products such as Cs-137, Co-60,

§b-125, Rh-102 and Eu.

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