768
MARTIN
equilibrium) about D + 30. The rateofdecline from D + 30 to D + 60 ap-
proximated the radioactive half-life of °*Sr. Estimates of the effective
half-life of **Sr in rabbit bone (T, = 20 days) were based on the average
rates of loss from plants and the average rates of accumulation in bone
ash, After estimates of the other required parameter values were ob-
tained, these and the observed values for B, were used to solve Eq. 5
for f,. The average value thus obtained was fp = 0.0575.
As shown in Table 2, the average concentrations of '*4I in plant
samples (sagebrush) from Groom Valley and the Currant Area were
higher than the average concentrations in the stomach contents of
rabbits from the same locations. In the Penoyer and Railroad valleys,
‘811 concentrations in the stomach contents of rabbits were somewhat
higher than those in plant samples (mostly shadscale) from the same
locations. Apparently the rabbits in these areas were feeding on plants
other than sagebrush and shadscale.
This supposition is supported by the estimates of f, given in Table
4, The average f, values based on the plant samples from all locations
are approximately the same for ®**Sr and '4I, However, the average
f, value for '*'I based on concentrations in plant samples is higher than
the average based on concentrations in the stomach contents of rabbits.
For both **Sr and ‘I, the f, values for sagebrush are higher than those
for shadscale. The differences between f, values for **Sr and ‘I in the
different study areas are probably due "to disparities between actual
and theoretical, a,, deposition rates, i.e., to fractionation or to errors
in the estimation of average gamma dose rates. In general, these re-
sults indicate that the plants (probably grasses and broad-leaved herbs)
representing the average rabbit’s diet were less efficient than sagebrush
but somewhat more efficient than shadscale in regard to the interception of fallout particles.
As shown in Table 2 and Fig. 4, the average concentrations of '*"I
in plant samples from all stations were higher than the average 13ty
concentrations in the stomach contents of rabbits from the Same areas;
Table 4—- ESTIMATES OF f, BASED ON EQS. 1 AND 2 AND OF INITIAL
CONCENTRATIONS OF ®srAND 111 IN PLANT SAMPLES, P,, AND OF
1311 IN THE STOMACH CONTENTS OF RABBITS, S)*
Study areast
Plant species
®Sr
Py
131]
Py
1917
So
Groom Valley
Penoyer Valley
Railroad Valley
Currant Area
Sagebrush
Shadscalet
Shadscale
Sagebrush
4.86
3.03
3.14
11.9
%107%
x10
«107
x10
5.61
1.56
2.21
7.02
x10
x1073%
x10
x10
2,42
2.32
2,24
4.51
x107%
x10°%
x10%
x107
4.40
x103
4.34
x107%
3.02
x1073
Average for all locations
*Py(®Sr) = 1.26 Ps, Po(8!I) =.2.00 Ps, and Sp(*841) = 2.00 Sx.
7 Locations of study areas are shown in Fig. 2.
fSome of the plant samples from this area were Grayia spinosa.