PERSISTENCE OF TRITIUM AND 4 IN THE PACIFIC PROVING GROUND
DESCRIPTION OF THE STUDY
Eniwetok Atoll is in the northern portion of
the Marshall Islands in the §.W. Pacific Ocean
(11°30’ N lat, 162°15 E long) and was a proving
ground for nuclear device testing from 1948 to
1958 when the last detonations took place. The
detonations occurred in various environmental
Islands on the eastern edge ofthe atoll. They
islands were adjacent to shot areas andreceiveg
close-in fallout from barge shots in the lagoon,
AomonIsland had a 49-kton towershot in 1943
A mapof Eniwetok Atoll with the island nam,
and craterlocationsis given in Fig. 1.
Sampling procedure
MC, the crater-forming shots were considered
examination of the Eniwetok environmentto
determine if tritium and !C are present in
most appropriate. Preliminary studies of a
large cratering detonation at the Nevada Test
Site have indicated that a significant fraction
of the residual tritium produced becomes
associated with the geological materials in and
displaced by the explosion.”
The detonations which produced a distinct
crater at Eniwetok Atoll were few (many shots
being madefrom barges within theatoll lagoon),
but two areas were selected for survey on the
basis of their physical and biological characteristics. Cactus Shot (1958 Hardtack Series) produced a terrestrial crater at the north end of
Runit Island on the eastern edge of the atoll.
The crater has a distinct lip and a throwout
zone of mounded coral sand and debris. Vascular plants have become reestablished on the
crater materials, and trees of Scaevola frutescens
and Messerschmidia argentea with diameters up to
4 in. at the crown are growing within 15 ft of the
crater lip. Mike Shot (1952 Ivy Series) created
a large submarine crater adjacent to Sanildefonso
Island. Thecrater is actually in the coral reef
This survey is intended to
be an initial
biological and soil materials at times up to 12
after detonation.
Because of the preliminary
natureof the survey,it was desirable to collect a
wide variety of materials without acquiring
excessively large numbersofsamplesfor analysis.
In some cases a sample series may be incom.
plete because of sample number limitations o
its unavailability at the time of collection. In
spite of some shortcomings and the preliminary;
nature of this survey, the data enable us to
describe in some detail the persistence oftritium
and *4C in the physical and biological materia
of theatoll.
The samples were collected on eight island
on EniwetokAtoll during July and August 1964.
This was the beginning ofthe rainy season in the
northern Marshall Islands. The University of
Washington, Laboratory of Radiation Biology
scientific staff was conducting a resurvey of
Eniwetok and Bikini Atolls at this time and
assisted in collecting the biological specimens.
that forms the oval platform on which the
It would not have been possible to obtain the
wide range of samples reported in this study
partially filled with coral sand since the shot
date.
At Japtan, Runit and Engebi Islands, wood.
green leaves, litter and a soil sample were
islands of the atoll have formed. The crater has
Otherislandsin the atoll not involved directly
in any nuclear detonation (but which undoubtedly received close-in fajlout of large particles)
were also sampled to provide information on the
generaltritium backgroundofthe atoll. Igurin
without their valuable assistance.
collected as an ecological series from the same
samplesite. A wood sample from the south end
of Runit Island was compared with the sample
from the north end at Cactus Crater. Wood
samples were also obtained from four other
sampled in this series. Engebi Island at the
islands.
Two plant species were often present in the
habitats of the detonation sites. These were
Triumfetta procumbens, a prostrate vine in the
This island was adjacent to many bargeshotsites
species were collected on Runit Island adjacent
Island at the southern end of the atoll and
Japtan Island on the eastern edge were islands
farthest from the detonation sites which were
northeast corner of the atoll was also sampled.
ee
tower shots were fired on this island. Collection
were also made on Aomon, Biijiri and Aaranbin,
situations within or near the atoll, but fur the
purposes of surveying for residual tritium and
tear
in the 1958 series, and in previous serig
Tiliaceae, and Lepturus repens, a short grass. These
T~
concentrations, and that they are presently
detectable at elevated levels in the biota.
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