CRITICAL ORGAN
———
109
"|mse
10-1
LyeNO
eee a:cn
1
|
|
;
Lungs
——
LE—<
According to the Task Group model (Figure 4 and Appendix A), thoracic lymph
nodes receive the highest dose (Figures 8 and 9) but the critical organs
;
recognized by ICRP (1959) are bone, if the Pu is "soluble," and lung if the Pu
is "insoluble." For relatively short exposure times, the model, which makes
no distinction between "soluble" and “insoluble,” predicts that the cumulative
dose to lungs would be considerably higher than the cumulative dose to bone
(Figure 8), but the cumulative doses to 70 years are about the same. For
@xposure times longer than 70 years, the dose to bone would be higher than the
dose to lungs. This is due to the relatively short biological half-Life of
plutonium in lungs (500 days) compared to that of bone (36,500 days). As the
estimated dose to lungs is higher than the estimated dose to bone, the exposure periods < 70 years, and the permissible dose to lungs is lower (see
below), the lung (i.e., the pulmonary region of the respiratory tract) is the
critical organ.
PERMISSIBLE DOSE CRITERIA
10-31
Current ICRP (1966) recommendations concerning "dose limits for individual
members of the public" indicate that the dose to lungs should not exceed
10-4
|---|--------]
"1.5 rems in a year." Annual dose rates to a given organ can be estimated on
the basis of predicted organ burdens as a function of exposure time,
For
present purposes, we shall consider only the equilibrium lung burden which,
for practical purposes,
is constant
for chronic exposure
times
in excess of
about 10 years.
ESTIMATION OF ASC
106°
|
10,000
er--7
Dose Commitment, rems
10-2
des
The acceptable soil concentration (ASC) is defined as the average concentration of
239Pu in the soil of an area occupied by the hypothetical Standard Man
which would result in a dose to the lungs equal to or less than the permissible
dose. This value is estimated as follows:
20, 00
Time, Days
S DUE TO 239 Pu IN
FIGURE 9, PREDICTED DOSE COMMITMENT
DIFFERENT ORGANS OF STANDARD MAN
ASC = (1.5/365)/(E ¥og/™ = 2817 pci(??’ pu) /p(soil)
where
(1.5/365) is the "permissible dose rate" in rem/day,
£ for 739pu is 51.2159 x 53 = 27144 (rem/day) /pCt or
0.0027144 (rem/day)/pCi,
681
680