water, radioactive materials began to accumulate on the hulls below the water line
and in the saltwater systems within the ships.
As a result, radiation intensities below
deck began to increase, adding to the crew's exposure.
When compared to the topside
radiation environments resulting from Shot BRAVO and Shot ROMEO fallout, this
radiation
was
"considered
more
of
an
operational
nuisance
than
a_
hazard"
(Reference 12).
The same phenomenon was observed on the ships at Operation CROSSROADS
conducted at Bikini Atoll in 1946. A model was developed in Reference 6 to determine
personnel exposure aboard the ships at CROSSROADS due to ship contamination.
Because only limited lagoon water contamination data have been found for Operation
CASTLE, this model cannot be applied directly to the ships participating at this
operation; however, several simplifying assumptions concerning the degree of contamination can be made, which allows portions of the mode! to be used.
Two basic assumptions are made in developing the ship contamination model.
The first is that the mixture of fission products present in the accumulated radioactive
material on the hull and in the piping of a ship decayed radiologically as tots},
This
decay rate was verified experimentally for fission products deposited in seawater and
on the decks of target ships at CROSSROADS.
The second assumption involves the
rate of contamination buildup on the hull and interior piping. The radioactive buildup
on a previously uncontaminated ship is assumed to be initially proportional to the
radiation intensity of the water surrounding the ship, but, as buildup progresses, a
limiting or saturation value of contamination is approached asymptotically.
The
occurrence of such a saturation effect is indicated by hull intensity readings taken on
various ships after their departure from the lagoon following CROSSROADS opera-
tions.
Based on these assumptions, the exterior ggmma intensity of the hull L(t) ofa
contaminated ship at time t is given by:
I(t) =
sh7[ exp {- Eo, 04] ,
28
(1)