the Effects of Atomic Radiafjon > and are equivalent to a bone-marrow dose
on calcium in bone and an endosteal cell dose
rate of 1.4 mrad/y per pCi
rate of 1. § mrad/y per pCi
7¥Sr/g calcium in bone. They are based upon the
ggtake of 24Sr relative to the intake of calcium, ihe residence time of
Sr in bone and the mean effective energy of the
Y beta
particles.
These conversion factors for endosteal cell and bone-marrow (32555) and dose
rates are calculated 1g two steps.
used to correlate the
bone.
First, the model of Bennett\
20Sr concentrations’ in diet with r36+ in mineral
Second, the dosimetric model developed by Spiers(29)
is used to
calculate the bone-marrow dose rate from the concentration in mineral bone.
Bennett's empirical model is developed from 90Sr concentrations from
world-wide fallout found-in foods and autopsy bone samples from New York and
San Francisco. It also includes age-dependent variations that allow us to
make dose estimates for children as well as adults. An estimate of the
calcium content of the normal Marshallese diet peyover 0.8 g/d, which 1S very
Similar to the 0.9 g/d estimated for U.S. diets
Thus, the
7*Sr uptake
and retention would be essentially the same as those developed by Bennett.
Using Spiers' model the dose rate D, to a small, tissue- filled cavity
in bone is calculated from the 90Sr concentration in mineral bone.
Then
from geometrical considerations, the dose rates to the bone marrow D,, and
endosteal cells D, are calculated using conversion factors 0,/D, = 0.31
and 0./D, = 0.62 respectively.
This is equivalent to a bone marrow dose
rate of q. 4 mrad/pCi-y/g Ca and an endosteal dose rate of 1-8 mrad/pCi-y/g Ca.
The above models and Gonversion factors are used to calculate the dose
conversion constant for
7¥Sr in Table 6.
137 The dose equation relating the various factors is similar to that for
C s but it is more difficult to determine the integrated pCi-d because the
90s model requires a numerical integration.
The base parameters are:
the average effective energy of 90s~ -90y beta particles = 1.13
Mev and is included in the W term defined below.
f1; = the gut transfer factor = 0.3 for 30 years.
E
W= the conversion factor from pCi of 90s in bone to the rad dose in
bone marrow = 1.4 mrad
pti-y
g Ca
= 1.4 x 1073 rad
pCi-y
g Ca
Z = the ratio of bone mass to calcium mass = 5g bone/g Ca.
Q= the term for the time 3integration representing the retention of 90s r
in the bone = 7.9 x103
pCi(pCi 7H) Intake
M= the mass of mineral bone = 5000 g
fF = the quality factor for beta particles = 1.0 rem
rad
9000113
0-8