-ll-
Island
BELLE
Figure 4 shows the decline
for island soil as well as the
only two observations for beach
sand at Belle.
The slope for
{sland soil of -1.06 (Table 1)
corresponded closely with that
of survey meter readings.
From an initial level on
the first day of 13 millicuries
per kilogram, the island soil
declined fairly regularly for a
period of two years. The dip
at 130-200 days is reflected in
the decline curves for land
hermit crab but is not apparent
in the data for green leaves of
plants on Belle.
Figure 5 shows the decay of
samples of island soil from Belle
DAYS
and of intertidal beach sand from Henry
A slope of -1.2 is in-
A
the basis for computation of the decay
correction factors for converting values
back to date of collection. The same
5
The Belle island soil decay curve
Sotl decay
Radioachivity
cluded for comparison.
is for plate number 7542 which served as
160
MAY 14, 1954
Fig. 4
(plate 7542) and from Edna (plate 9170),
(plate 9711A).
APTER
factors were used for all types of
material except rats collected post-
Nectar at Eniwetok Atoll.
The dashed,
early portion of the curve is not a
straight line because it was originally
;
1
at
76
we
Days ofter May #50
Fig. 5
extrapolated on semi~log paper.
For comparison, Figure 6 shows the
Mtike soi/ decay
decay of the sample of lagoon bottom sand
dredged November 7, 1952 off Tilda (north1952(Donaldson 1953:25), and for 20-1000
days its similarity to the theoretical
curve of Figure 2 is striking.
It was
practically uninfluenced by residues from
previous detonations.
The more pronounced
flexures in the curve for Belle island soil,
&s well as its generally more gradual slope
&re the result of the influence of the Mike
test residues superimposed upon the Nectar
test effect.
&
rT
This decay was used for _
calculation of decay correction factors for
the collections following the Mike test in
tivity
= Radiewc
Tt
west of Vera).
Dayt after Mevember 1, 52
Fig. 6
1600